Re: [Qgis-user] Process Land Cover Raster Data

[Andrew Harfoot via QGIS-User]

Hi there Richard,

The simple array format that your data is in means that it can be read 
by GDAL using the ESRI HDR driver:

https://gdal.org/drivers/raster/ehdr.html#raster-ehdr

This just requires a sidecar file named /clt02.hdr/, that contains the 
information for QGIS to interpret the binary array. I modified the 
example in the page above to create this, and saved it in the same 
folder as the data:


ncols 4000

nrows 4000

cellsize 25

xllcorner 1589000.00

yllcorner 6135000.00

nodata_value .00

nbits 16

pixeltype SIGNEDINT

byteorder msbfirst


Load the original binary file into QGIS and the hdr will be read 
automatically. It won't have a coordinate system assigned, but that can 
be done using the Assign Projection processing tool within QGIS, which 
will create a /clt02.prj/ file in the same folder containing the NZ CRS 
details.


The number of bits can be calculated from the file size, but I have 
guessed that the data is a (standard) signed integer, and indeed the 
values look reasonable (30-37).
Using the index file, equivalent .hdr files could be built for all the 
NZ tiles


The excellent Serval plugin can then be used to edit the raster values 
in place.


Cheers,

Andy


On 01/09/2023 07:28, Richard & Mary via QGIS-User wrote:

*CAUTION:* This e-mail originated outside the University of Southampton.

Greetings Team

I work as a Radio Engineer in the NZ Public Safety Sector and a 
planning tool that I work with uses a land cover and elevation rasters.


New Zealand is divided up in series of 100km tiles each tile is 4000 x 
4000 representing a 25m square.


The contents of these files are a binary number from 0 to 50 
representing individual land cover categories, or 0 to approx 5000 
representing the elevation



Each of these tiles has a Xmin and Xmax for Easting and a Ymin and 
Ymax for Northing on the NZTM2000 grid.


*I want to be able to display and edit these 25m squares to fix some 
errors that affect our radio modelling.*



I am using QGIS 3.28.10 and have tried a variety of Raster imports but 
get a not supported format.


The file format is know as MSI Planet and is one of the default 
formats used for land cover in the radio coverage modelling tools.


I have attached a sample of the clutter file (this one was 31.25MB 
before zipping) I have also attached the index which show where on the 
NZTM2000 grid this tile resides.


I also have the same files in a format used by EDX which embeds the 
East - West North South Limits and the projection, but these are 
generated from the initial plain raster.



I have read some information about using satelite image stacks to 
generate land cover information, if I do that i need to be able to 
output the plain 100km x 100km block



I would be interested to any help you can give me.

Richard Hutchinson


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Re: [Qgis-user] problem with cartographic label placement

[Andrew Harfoot via QGIS-User]

Hi Uwe,

I've not attempted to deal with this issue before, but it occurred to me 
that you might be able to use two labelled layers (duplicates) one 
locked to each position, using the labelling priority weighting to apply 
the ranking. the only issue is that in sparse data areas both labels 
might be drawn, so you may need to ensure that there is sufficient 
overlap between the two positions to prevent this.


Cheers,

Andy

On 19/01/2023 13:14, Uwe via QGIS-User wrote:

*CAUTION:* This e-mail originated outside the University of Southampton.

Hello Andreas and list,

I am sure I’m not the first one to encounter the problem described 
below. So I would like to ask again. Maybe someone has an idea?


thanks a lot, the solution from Andreas is working.

But the result is not as desired. I was hoping to be able to define a 
ranking of placement alternatives. That is (in case of ‘B,R‘): place 
all the labels at the bottom and only if there is a conflict (overlap) 
with something else place a label at right.


But what I get is: most oft he labels are placed right, even without 
overlap problems (although I put ‘R‘ at the second place of the list). 
And only a few labels are placed at bottom.


However, the overlap problem is solved.

Is there something I could improve?

Thank you and best regards, Uwe

*Von:* Andreas Neumann 
*Gesendet:* Donnerstag, 12. Januar 2023 22:18
*An:* gisfi...@t-online.de
*Cc:* qgis-user 
*Betreff:* Re: [Qgis-user] problem with cartographic label placement

Hi Uwe,

I just tried it. 'B,BR' worked for me. Just don't use quotes before 
and after the separator.


Greetings,

Andreas

On Thu, 12 Jan 2023 at 22:02, Uwe via QGIS-User 
 wrote:


Hello list,

for cartographic label placement, according to the help docs it
should be possible to define position priorities in a ranking.

But when I open the editor and enter a comma separated list like:

‘B‘ , ‘BR‘

I get an error message. Entering just one value it works. But that
doesn’t make sense because I need at least two values to let the
label move when it collides with a feature.

What can be wrong with my input? I use 3.28.

Thanks a lot for help.

Uwe

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Re: [Qgis-user] Labeling with subscript

[Andrew Harfoot via QGIS-User]

Hi Christian,

If the subscript data is just numbers you can have a look at this post:
https://gis.stackexchange.com/questions/181287/achieving-super-or-subscript-graticule-labels-in-qgis-composer-windows

As this is a custom expression function it is applicable to labels as well.

Cheers,

Andy


On 05/01/2023 13:32, Bodamer, Christian via QGIS-User wrote:

*CAUTION:* This e-mail originated outside the University of Southampton.

Hello list,

wish you a happy NEW YEAR!

I like to label with two columns. The secound column sholud be 
subscript. I activate HTML Formating and use the following code in the 
Value field:


format(

'%1 Sub%2',

   "column1" ,

   "column2"

)

The text of column2 is displayed but not subscript. Also %2 
doesn't work.


Changing the color with style="color:red" works. I don't see the mistake.

Does someone has an idea?

Christian

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Re: [Qgis-user] large DEM not loading tiles correctly

[Andrew Harfoot via Qgis-user]

Hi Michael,

Here are some instructions to do exactly what you are asking that I 
recently wrote for someone else (you are not alone!):


The ESRI ASCII grid format is supported by QGIS, and will load as a 
raster if you drag an .asc file over the map canvas. The further 
complication with the gridded dataset is that it is split into 10km 
tiles rather than being a single national layer, so needs to be merged 
before moving on to the next steps. This is fairly straightforward using 
the following steps:


1. Unzip the downloaded data. You'll notice that the 10km tile files are 
also zipped, and each placed in a 100km square folder: 
hp\hp40_OST50GRID_20220506.zip


2. Move the zip files out of their 100km square folders to make it 
easier to process them all at once. This can be done through File 
Explorer by searching in the folder below the 100km square folders for *.zip


You should get 2858 results. Select all of these files using Ctrl + A 
and then drag them into the data folder - they will be moved out of 
their individual 100km square folders


3. Unzip all the zip files. I don't think that the built in Windows zip 
functionality can do this in one go though. I use the open source 7zip 
software which allows a bunch of zip files to be selected in File 
Explorer and then from the right click menu, 'Extract Here' can be 
chosen. You should now see a .asc file in the folder for each 10km grid 
square, eg: HP40.asc. This is the grid data.


4. Merge the 10km tiles together. This is done in QGIS using the Merge 
tool from the Processing toolbox (or Raster > Miscellaneous > Merge...). 
In the Input layers section, click the ellipsis button to open the file 
selector, and use the 'Add File(s)...' button to add the .asc files (if 
you sort by file type you can select them as a block).



Fill out the rest of the Merge tool dialog like this:


Clicking Run will start the process, which may take some time, but on 
completion you should have a single national terrain dataset!



Cheers,

Andy


On 28/09/2022 12:32, Michael.Dodd via Qgis-user wrote:

*CAUTION:* This e-mail originated outside the University of Southampton.

I am trying to put together the 50m uk DEM e.g. 
https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm 
 
but it often does not work.  The data are supplied as thousands of 
small tiles that takes ages to unpack and put into a folder to get 
into qgis, however when you try to load the tiles some work and others 
don’t and even the ones that do work and display fine sometimes don’t 
merge to form large tiles and sometimes will form virtual rasters but 
not merged files.  Basically it is a mess.  I suspect others have done 
this successfully so any suggestions?


It is particularly odd that some of the tiles will merge and others 
won’t and that some won’t display if you ask it to load hundreds at a 
time but if you just add them in a few at a time then they will load 
and display (in addition to the hundreds already loaded). This 
suggests various bugs assuming the original data are not in a whole 
variety of slightly different formats (should all be .asc)



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Re: [Qgis-user] Geolocating .flt files

[Andrew Harfoot]

Hi Gary,

Looking at your snippet of the hdr file, the dataset appears to be an ENVI 
raster see:
https://www.harrisgeospatial.com/docs/ENVIHeaderFiles.html

These rasters can be opened by QGIS (via GDAL as Richard states). The relevant 
notes are here:
https://www.gdal.org/frmt_various.html#EHdr

The fact that QGIS is loading the raster is good, but it may be that QGIS is 
also already reading the georeferencing data. A good way to check is to open 
the layer properties of the dataset and look under the Information tab. Here 
you should see various properties of the image reported, looking at the geo 
points info that you supplied, the CRS should be a geographic (Lat/Lon) system, 
and the extents will be roughly 145 to 148° W and 40 to 44° S (Tasmania?). Do 
the coordinates reported by QGIS match this? If so then it would appear that 
QGIS is reading the information in the hdr file correctly!

If the information isn't being read, one possibility is that the hdr file 
doesn't follow the naming convention that GDAL is expecting - if the image is 
called data.flt, then GDAL will expect the header file to be data.hdr, and not 
data.flt.hdr. If the latter, then try renaming  the file.

Cheers,

Andy

On 09/05/2019 10:31, Quinn, Gary wrote:
I am new to Qgis.

I have an .flt (floating point raster) file and an associated .hdr file.
I can import the .flt  image file into Qgis (using Add raster layer), and the 
image displays correctly.
But how do I geolocate this image using the associated .hdr file?
In other words, how do I make Qgis use the .hdr file to let me know the lat/lon 
of each pixel on the display?

Note: The .hdr file is like this:
geo points  = { 1, 1,  -40.212464,  146.355212, 1,  2590,  
-44.006326,  145.100364,  1024,  2590,  -44.252673,  146.901021,  1024, 1,  
-40.442148,  148.049722}

So I want Qgis to use this .hdr information to geolocate the image.
I have searched various info about using .flt images and geolocation but can't 
find anything.

Appreciate any help.

Thanks


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Chief Engineer
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www.essweather.com
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Re: [Qgis-user] Featured plugins: nominations

[Andrew Harfoot]

On 24/01/2019 12:48, Micha Silver wrote:


I'd like to see all plugins arranged in categories: Dev tools, 
Hydrology, CAD, Classification, Vector tools, Web, etc...


The number of plugins is fast reaching the point where this is necessary.

Or make the existing tag system more visible when searching ie an 
explicit filter by tag option?


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Re: [Qgis-user] Dissolve tool failing to produce outputs

[Andrew Harfoot]

Just to add that the equivalent dissolve tool in 2.18.25 completes 
successfully on the data.


On 19/11/2018 14:47, Andrew Harfoot wrote:


I'm seeing very strange behaviour with a particular shapefile in QGIS 
3.4.1. The data can be obtained here:


https://drive.google.com/file/d/1BPVnsUbJREYh6TvLM07GAzXMiMneHemN/view?usp=sharing

When I run the /Vector Geometry > Dissolve/ Processing tool on it, no 
errors are raised, an output layer is created containing one row with 
no geometry. This happens regardless of the Processing 'Invalid 
features filtering' setting.


Running the /GDAL > Vector geoprocessing > Dissolve/ tool on the data 
immediately returns an invalid geometry (self intersection) error, but 
running /Vector Geometry > Check validity/ finds no errors using 
either the GEOS or QGIS engine.


If the /Vector Geometry > Dissolve/ tool is run on a selection from 
the shapefile, it will complete successfully if all but one feature is 
selected, *regardless of which feature is left unselected*.


I'm not sure whether this is a bug, or my data. Does anyone have any 
explanation for the observed behaviour?


Cheers,

Andy

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[Qgis-user] Dissolve tool failing to produce outputs

[Andrew Harfoot]

I'm seeing very strange behaviour with a particular shapefile in QGIS 
3.4.1. The data can be obtained here:


https://drive.google.com/file/d/1BPVnsUbJREYh6TvLM07GAzXMiMneHemN/view?usp=sharing

When I run the /Vector Geometry > Dissolve/ Processing tool on it, no 
errors are raised, an output layer is created containing one row with no 
geometry. This happens regardless of the Processing 'Invalid features 
filtering' setting.


Running the /GDAL > Vector geoprocessing > Dissolve/ tool on the data 
immediately returns an invalid geometry (self intersection) error, but 
running /Vector Geometry > Check validity/ finds no errors using either 
the GEOS or QGIS engine.


If the /Vector Geometry > Dissolve/ tool is run on a selection from the 
shapefile, it will complete successfully if all but one feature is 
selected, *regardless of which feature is left unselected*.


I'm not sure whether this is a bug, or my data. Does anyone have any 
explanation for the observed behaviour?


Cheers,

Andy

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Re: [Qgis-user] z factor in aspect calculation?

[Andrew Harfoot]

I'd agree, the aspect of a slope does not vary with it's gradient, and 
the scale factor is only used to ensure that the gradient calculations 
are made using consistent units in XY & Z.


Cheers,

Andy

On 11/10/2018 19:43, Nicolas Cadieux wrote:

Hi,

I use a z factor in slope and hill shade calculation when my DEMs are 
in Long/Lat and the altitudes in metres (like SRTM, ASTER GDEM...).  
In GdalDem , there is not a z factor or a scale option for Aspect 
(0-360D azimuth) but in the Qgis terrain analysis, there is. (It does 
not appear to work in Qgis 2.18.24).


In Qgis 3.2.3, when using the QGIS Terrain analysis Aspect algorithm 
with a z factor of 1, I get identical results as in gdaldem and 
results look and feel good.  I figure it's probably the same algorithm 
running in the background.  What more,   the aspect file is similar to 
result done on a reprojected DEM in a local UTM zone (where no z 
factor is needed as everything is in metres).  Reprojecting is not an 
option for my project.


In the QGIS Terrain analysis Aspect algorithm, if I use 0.126 as 
the correct z factor for the area (1 / The length of a Degree of 
Longitude in metres at a latitude of 45N) (or 1/78847=0.126)  my 
results are very wrong.


I wonder if using a z factor (0.126) is not needed for the aspect 
calculation and that this should be removed from the QGIS Terrain 
Analysis aspect options.  Any thoughts?


Nicolas



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Re: [Qgis-user] Hot Spot Accumulation

[Andrew Harfoot]

For circles of a specific size, one per input data point you'll need to 
build your own using tools from the Processing toolbox:


1. Use the Buffer tool on the input points to 200m to create the circles
2. Use the Join attributes by location tool to attribute the circles 
with counts and / or weighted counts of the input points falling within 
each.


Cheers,

Andy


On 27/09/2018 12:53, GILLEN Finbar wrote:


Hi Nicolas,

I checked that but it doesn’t create a singular circle for each point. 
In more dense areas it will merge the circles as one.


I would be looking for an individual circle for each point.

Regards

Finbar

*From:* Nicolas Cadieux 
*Sent:* 27 September 2018 12:51
*To:* GILLEN Finbar 
*Cc:* qgis-user@lists.osgeo.org
*Subject:* Re: [Qgis-user] Hot Spot Accumulation

Hi,

I believe heat map will do that. You can use weight from field.

http://www.qgistutorials.com/fr/docs/creating_heatmaps.html

Nicolas


Le 27 sept. 2018 à 07:42, GILLEN Finbar > a écrit :


Hi All,

Is there a plugin or tool within QGIS that creates a hotspot for
each individual point in a dataset and assigns a score based on
the amount of points that fall within a given radius, say 200
metres (See image below)?



I would be looking to weight the score with a variable within the
dataset to.

Regards

Finbar

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Re: [Qgis-user] Digitizing points with azimuth and distance

[Andrew Harfoot]

On 05/03/2018 08:20, Paolo Cavallini wrote:

Hi all,
I cannot recall an easy solution for this problem:
* clicking on a point
* adding azimuth an distance
* automatically creating a point, in a second layer, at the distance and
azimuth specified
* repeat the procedure, adding more point to the same second layer.
Anyone has a good solution to this?
All the best, and thanks.


Have you had a look at the CoGo plugin:

https://github.com/kartoza/parcel_plugin/

Cheers,

Andy

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Re: [Qgis-user] stich together osm tiles to get a say a0 map

[Andrew Harfoot]

Hi Richard,

Have you had a look at the GDAL WMS Driver - this can be used with other 
GDAL commands to connect to tile services and save out to a file based 
format for offline use. Look at the OpenStreetMap TMS Service Example in 
this page:

http://www.gdal.org/frmt_wms.html

Cheers,

Andy

On 10/09/2017 15:46, Richard Duivenvoorde wrote:

Hi,

Anybody experience with using QGIS to stitch together OSM tiles to
create a big image/map on a certain z-level?

Context: a big (georeferenced) image to be used as reference offline,
OR to be used as an input layer for gdal2tiles.py

Most plugins work on 'current canvas' while it would be cool to be able
to create a 'virtual' canvas on which QGIS then print it's vectors or
(web)tiles and then could as a whole be saved as a big georeferenced map.

Any idea's?

Regards,

Richard Duivenvoorde
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Re: [Qgis-user] Cartography of the Azores

[Andrew Harfoot]

Hi Sarah,

I've used Maperitive (http://maperitive.net/) in similar situations to 
download OpenStreetMap map tiles and store them in a local MBTiles 
database, from where QGIS can load them very quickly!


Rough steps are:

1. Decide on your web mapping
2. Set the bounds using UI, or running this command (edit min/max Lat/Lon):

set-geo-bounds 96.1,19.2,97.7,22.4

3. Export to MBTiles (edit min/max zoom and path):

generate-mbtiles minzoom=5 maxzoom=14 
file="C:/Projects/Test/Southampton.mbtiles"

4. Load the MBTiles file into QGIS!

This still requires an internet connection to download the data, but the 
process can be left running overnight etc.


Cheers,

Andy

On 12/03/2017 12:28, Sarah Gregg wrote:
Hi everyone. I'm working on a project based in the Azores and wondered 
if anyone knew of any reasonably good free topographic base maps I can 
download, strictly for non commercial purposes. At the moment, I'm 
trying to use the OpenLayers plugin, but I have a VERY slow internet 
connection which makes OpenLayers or WMS frustratingly slow to load. 
Thanks in advance for any ideas, Sarah.




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Re: [Qgis-user] Question on Spatialite

[Andrew Harfoot]

Another option would be to do this in the DB Manager - ie use the SQLite 
engine directly, but you would have to recouch your Field Calculator 
expression as SQL.


Andy

On 01/03/2017 22:33, Randal Hale wrote:
Attribute! Used Field Calculator to split an attribute to get the 
zipcode into a standalone column. I then hit save and watched the fun.


And yes that seems to be it. Good, I'm not crazy (on this issue).

Randy


On 03/01/2017 05:23 PM, Nyall Dawson wrote:
On 2 March 2017 at 08:08, Randal Hale 
 wrote:

I'm using 2.18.4

I'm working with Address point data. My typical process is to import 
the

data into PostGIS/Postgresql and work with it. I decided to work with
spatialite and do some data cleanup.

I have 222519 points. I made a change to all of them and hit save.
What change did you make? Attribute or geometry? How was this change 
made?


It possibly relates to this ongoing work: 
https://github.com/qgis/QGIS/pull/4175



Nyall


So for
the next 20 minutes I watched a very small journal file appear and 
disappear
and QGIS just locked up until it was done. QGIS returned to normal 
and I'm

working along again.

So my question is - Can I avoid this happening easily or is this just a
"it's what happens with spatialite" problem? Am I missing a setting
somewhere?

Randy


--

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North River Geographic Systems, Inc
http://www.northrivergeographic.com
423.653.3611 rjh...@northrivergeographic.com
twitter:rjhale http://about.me/rjhale
http://www.northrivergeographic.com/introduction-to-quantum-gis
https://www.facebook.com/NRGSInc

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Re: [Qgis-user] Applying cumulative usage to road sections

[Andrew Harfoot]

I think this can be solved in two stages:

1. Given the transport network, source and destination locations, a 
shortest path calculation run repeatedly should generate a series of 
routes. Commonly these functions output the route in terms of a list of 
the network sections to follow.


Options for doing this calculation in QGIS include: PostGIS (pgRouting), 
Spatialite, GRASS v.net functions, QGIS Road Graph plugin


2. Once the routes have been generated, then they can be combined and 
summarised to generate the total weight traversing each network section, 
which would probably be as a new table that would be joined back to the 
network. This step could be done within a database (PostGres, Spatialite 
etc.), in core QGIS, or even Excel.


Cheers,

Andy


On 15/01/2017 21:07, rossnixon wrote:

I don't know if the following can be solved with a QGIS plugin. In MapInfo it
requires a 1500 Euro add-on.
But perhaps someone has had a similar problem in the past? Maybe with road
networks, or watercourse volumes?

I would like to calculate the total 'weight' of goods which will travel
across *each* road section.
Goods will arrive at the closest road section, and then travel along
subsequent road sections to the destination. So, road sections nearest the
destination will have multiple loads travelling over it which need to be
added together. Example image attached.




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Re: [Qgis-user] Display pictures at points

[Andrew Harfoot]

Untested, but (in 2.18 and possibly earlier) you can create Filled 
Marker styles with a raster image fill, and the source of the raster can 
be data driven. Worth a try?


Cheers,

Andy

On 11/01/2017 17:42, Josef Fürst wrote:

Dear QGIS users,

I am switching over more and more from ArcGIS to QGIS. Many features 
are really much nicer.
But now I am needing a feature that displays small pictures 
(pictograms) at all points of a point shapefile. Similar to diagrams, 
but these specific diagrams are already available in PNG (or JPG) 
format. An attribute of the point shapefile contains the filenames of 
the pictures. I can display these pictures interactively point by 
point using either eVIs Browser or Action, even HTML maptip. But I 
want to see them all together on the map like other point symbols (or 
diagrams).


Any idea? Some existing script or plugin that I can use as a starter? 
Or maybe I am just missing an existing feature?


Thank you!

Sepp


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Re: [Qgis-user] best data storage fo time series visualisation in QGIS

[Andrew Harfoot]

I saw a demo of the Crayfish plugin at the FOSS4G-UK conference earlier 
in the week, and it provides 'time slider' functionality for netCDF 
based data, plus additional tools such as video generation. Worth taking 
a look?


Andy

On 17/06/2016 10:29, Régis Haubourg wrote:

Hi,
I need the communities lights!

I'm starting to work with huge meteo datasets composed of a grid of 
point layers, and hundred of millions of rainfall / temperature data.


Datasets are delivered in a custom text format, so I'm digging around 
on what are the best formats for storage, use in postgis and QGIS.

I would like to be able to :
 - run timeManager to generate videos
 - display data averaged on day / month / year (or any other) timeframe
 - feed R analyses.

Up to now, I tried the following paths:
  - netcdf  / grib:  ideal for data storage:
  Pros : GDAL and QGIS can view it. R And python scipy have 
providers for that
  Cons : not easy to generate from exotic datasources, Current 
QGIS Netcdf explorer or core date visualisation (time frame = raster 
bands)  are not handy for daily data over decades (about 10 000 days 
available in my dataset).  I didn't manage to build netcdf yet, FME or 
GDAL are a bit dry..


 - load all in postgres / postgis relationnal model:
  Pros: available for all clients and fast, if data is 
correctly indexed and designed/
  Cons: performance requires a table (not a view because of 
lack of estimated metadata for extent computing) with redondancy over 
point location. I tried a first approach with a small geographical 
table for my point grid and a value table. With correct indexing and 
clustering, I get good performance in psql but very poor in QGIS. 
First load is slooow because of the st_extent query, but also every 
fetch afterwards, even if I filter on a date frame (with good index). 
I didn't expect it to be slow on fetch..


Another point with postgis storage, TimeManager plugin does not like 
true date datatype, date cast to char truncate date to first 
character,  so I have to expose my datasets with a text format in my 
view, which is not quite efficient.  (I will create a ticket upstream)


*Does anyone has any experience and advices on that field ? *
*
*
 I saw that postgis has a datacube type, could that be a way to store 
data more efficiently? Could QGIS read it? Should I stick with netcdf ?


Thanks a lot

--
Régis


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Re: [Qgis-user] Classification from a CSV

[Andrew Harfoot]

How about creating some dummy geometry by appending a WKT string of the 
appropriate geometry type to each CSV row, then that can be plotted, 
allowing the db values to be read to generate a style.


Andy

On 19/05/2016 15:03, Lene Fischer wrote:


Hi,

Is there a workaround to import classification values into 
Style>classification dialog.


I have 45 values in a db table and want to add these into this dialog.

I don´t have any features in the table.

Regards

Lene Fischer



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Re: [Qgis-user] QGIS project with no projection

[Andrew Harfoot]

Hi Simon,

Sorry for the confusion - GeoTiff is a standard for embedding the 
georeferencing information within the tif image file. A GeoTiff will 
usually contain the CRS information as well. A tfw file is an example of 
a world file, not a GeoTiff. It is an alternative approach to conveying 
georeferencing information, with the drawback of not also documenting 
the CRS of the georeferencing as you say.


Any possibility of sharing the image in question to allow people to 
suggest solutions?


Cheers,

Andy

On 11/05/2016 10:07, simonc8 wrote:

Thanks for all the responses.

I've tried the various suggestions but can't get my tiff to import properly
without specifying a projection. Even following the steps suggested in Lee
Hachadoorian's post the tiff imports and appears to show the correct units
in the information bar but when I measure distances using the Measure tool
these are nothing like what they should be.

Incidentally a geotiff doesn't necessarily have any projection information -
if you have a .tif file and an accompanying .tfw file it will merely
register the image using the coordinates specified in the .tfw file with no
information about what these refer to.



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Re: [Qgis-user] QGIS project with no projection

[Andrew Harfoot]

QGIS is configured into a non-earth or local CRS mode by doing the 
following (in 2.14):


1. Turn off 'On the Fly CRS transformation' (Project > Project 
Properties > CRS)
2. Ensure that the measurement ellipsoid is set to 'None / Planimetric' 
(Project > Project Properties > General)
3. Set the coordinate, distance and area units to 'Map Units' (Project > 
Project Properties > General)


All of these can also be set in the application level settings as the 
defaults. QGIS can also be prevented from prompting for a CRS when 
loading data that does not have one (QGIS still assigns a CRS, but 
essentially it is ignored, so this isn't quite what Simon was asking 
for, but close)


The LocalCoordinateSystemSetter in FME creates custom CRS for features 
passing through it, optimising them for equal area or distance. The same 
customised CRS could be implemented in QGIS, what is missing is a tool / 
plugin that would automatically generate them.


Cheers,

Andy

On 06/05/2016 17:03, Jonathan Moules wrote:
There have been some more knowledgeable responses than mine, but they 
do make me ask:
Why doesn't QGIS have a generic Coordinate System for X/Y in meters 
(and maybe one in feet for the less developed nations ;-) )? It would 
be particularly useful for non-geographical datasets and would open 
QGIS up to being used more readily in other fields.


Similarly, it could have generic projections for equal area and equal 
distance calculations too. I know these are all possible because FME 
has all these features.

After all, there's no reason spatial data has to be GEOspatial data.

Cheers,
Jonathan



 On Fri, 06 May 2016 16:28:45 +0100 *Lee 
Hachadoorian* wrote 


Simon,

You *must* specify a projection, but within some limits, the
projection doesn't matter. Basically, if the GeoTIFF uses units of
meters and you want your distances in meters, you can load the
GeoTIFF in *any* projected CRS that uses meters. An example would
be to use any of the UTM zones. You cannot use a lat-long CRS such
as the default WGS 84, because QGIS will convert (naively, *not*
using great circle distances) from decimal degrees to meters.

Once the layer is loaded, all geometry calculations are done in a
Cartesian plane.

I answered a similar question on GIS.SE  regarding
someone who wanted to use QGIS to map indoor location data.


http://gis.stackexchange.com/questions/187699/how-to-create-a-qgis-map-of-unprojected-data

Best,
--Lee

On Fri, May 6, 2016 at 10:12 AM, Jonathan Moules
mailto:jonathan-li...@lightpear.com>> wrote:

Hi Simon,
If you know the real-world width and height of the area
covered on the image, could you not geo-reference it to have
lower-left at 0,0, and then the top-right at the applicable
location in the projection of your choice, and then work from
there?

The problem is picking an applicable projection. I can't see
any generic "X,Y" projection, let alone one that is suited to
equal-area or equal-distance in the projections list. They may
exist, I'm just failing to find them. They all seem to assume
they're "somewhere" in the world (which can be a problem if
the data is spatial but not geographical).
Personally if it's a relatively small area (a few km across),
I'd probably just use a standard Mercator for the applicable
part of the world probably.

Cheers,
Jonathan



 On Fri, 06 May 2016 13:33:47 +0100
*simonc8mailto:simoncrom...@onetel.com>>* wrote 

I want to use QGIS to make measurements such as distances
and angles on a
flat scaled image which I have as a georeferenced tiff. I
don't want to use
any projection - just a straightforward orthogonal linear
scale in metres.
QGIS seems to require that I choose a projection. What
would be the best
choice for my needs? Can I make a custom projection with
no ellipsoid or
datum?

If I import my geotiff and don't specify a projection QGIS
assumes my units
are in degrees rather than metres, which will make
measurement of distances
and angles inaccurate.

Grateful for assistance.



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Re: [Qgis-user] QGIS project with no projection

[Andrew Harfoot]

Hi Simon,

Surely if your image is georeferenced, then it will have been done so to 
a CRS (not necessarily a projected one though). However, if you don't 
know the CRS (and it appears that QGIS cannot extract it from the 
GeoTiff if it is prompting you), but you do know the georeferenced units 
used, then you can achieve what you ask by disabling on the fly 
reprojection in QGIS. This has the effect of disregarding CRS 
information, and treating the coordinates of the data as cartesian (even 
if they are geographic). Distance and area are measured on the plane. If 
you set the measurement units under Project > Project Properties > 
General to 'Map units', then they will be the units of the data, 
regardless of what QGIS actually thinks they are.


Cheers,

Andy

On 06/05/2016 13:33, simonc8 wrote:

I want to use QGIS to make measurements such as distances and angles on a
flat scaled image which I have as a georeferenced tiff. I don't want to use
any projection - just a straightforward orthogonal linear scale in metres.
QGIS seems to require that I choose a projection. What would be the best
choice for my needs? Can I make a custom projection with no ellipsoid or
datum?

If I import my geotiff and don't specify a projection QGIS assumes my units
are in degrees rather than metres, which will make measurement of distances
and angles inaccurate.

Grateful for assistance.



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Re: [Qgis-user] custom string formatting for grid coordinate labels

[Andrew Harfoot]

I have just posted a couple of unicode superscript and subscript 
functions to GIS Stackexchange:

http://gis.stackexchange.com/questions/181287

Cheers,

Andy


On 18/02/2016 13:15, Claas Leiner wrote:

Hi,

With Unicode Characters is a good idea. As the code is implemented 
directly in a QGIS-Expression me remains a mystery.
I have searched for the mark on LibreOffice (insert special 
characters) and then copied using CTRL-C / CTRL-V in the expression.


With this expression:

Case
when @grid_axis = 'x' then (substr(@grid_number ,1,5) || '⁰⁰⁰ ᴱ')
when @grid_axis = 'y' then (substr(@grid_number ,1,5) || '⁰⁰⁰ ᴺ')
end

Do I get the coordinates marking shown in the attached image.

Best wishes

Claas


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Re: [Qgis-user] custom string formatting for grid coordinate labels

[Andrew Harfoot]

Hi Uwe,

If you can't use formatting tags, then possibly Unicode is your friend 
here - have a look at characters U1D31 and U1D3A - superscript E and N 
respectively. Using these should allow you to generate labels like this: 
0234ᴱ  or 345389ᴺ


Cheers,

Andy

On 16/02/2016 18:48, Nyall Dawson wrote:



On 17 Feb 2016 2:20 AM, "Uwe Fischer" > wrote:

>
> Hello List, hello Nyall,
>
>
>
> I have a question concerning the grid coordinate labels for map 
frames in print composer. If you set the label format to „custom“, you 
get to „Expression based annotation“ box where you can build 
expressions for formatting, e.g. concat(left(@grid_number,3) ,  
'E'). That works fine in the editor and the footnote preview 
shows exactly the desired result (E as an above positioned little 
index). But, in the map composer canvas, the format string is rendered 
as text, that means E shows up as a text string there.

>
>
>
> Is there a way to apply the format rule (which seems to work) 
correctly to the map composer?


Not currently - there's no support for formatting in the coordinate text.

Nyall

>
>
>
> Regards and thanks a lot,
>
>
>
> Uwe
>
>



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Re: [Qgis-user] Set default view for Identify window?

[Andrew Harfoot]

Hi Robin,

Have you tried using the Value tool plugin as an alternative? I think it 
predated the addition of the raster specific elements to the core 
Identify tool, and offers greater functionality. I particularly like it 
as it is a separate panel, not tied to the identify tool, without adding 
another button. It also offers multi layer views and customisable band 
combinations. NoData values are shown as zero - which may or may not be 
an improvement, but as it's Python based, you may have more luck 
customising it.


Cheers,

Andy

On 20/10/2015 19:14, Robin Wilson wrote:
On 20 Oct 2015, at 12:14, Nathan Woodrow > wrote:


I'm keen to kill that dock and replace it with something better in 
the next version or version after.  Open to ideas on that.




Did you have any specific ideas yourself?

I'm keen to see it work as well as possible - it's one of the bits of 
QGIS that I use the most (I write most of my analysis code in separate 
standalone Python scripts, and then use QGIS for investigating and 
visualising the output). The table and graph views are great - but 
possibly need a bit of work (eg. I opened a bug report on an issue 
with the graph and NaN values in bands - see 
https://hub.qgis.org/issues/13639). I still far prefer it to the 
equivalent windows in other tools (ArcGIS, for instance).


Robin



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Re: [Qgis-user] QTiles using

[Andrew Harfoot]

Hi Sebastian,

If your aim is to load the output of QTiles back into QGIS then I would 
recommend that you set QTiles to generate a mbtiles file (choose to 
output to file, and change the file type to mbtiles). These files will 
load into QGIS.


If you need to create the individual tiles as files, then you can create 
an XML file describing the tiles that you've generated, and open that in 
QGIS. The XML structure is described here: 
http://www.gdal.org/frmt_wmts.html. If you tick the 'Write .mapurl file' 
option then this file contains much of the info needed for the XML.


Cheers,

Andy

On 28/10/2015 21:47, Sebastian Teßmer wrote:

Hello there,

I use the extension QTiles and there were tiles created.
Unfortunately, these are not georeferenced.
How can I make this again involved as a map in QGIS?

Many thanks,

Sebastian
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Re: [Qgis-user] Modeler-only tools: Calculator

[Andrew Harfoot]

On 09/08/2015 15:07, Bernd Vogelgesang wrote:

There seems to be no way to get rid of that function from the model
manually in a text editor, identifying the section and removing it still
leaves a crippled model which refuses to load.

Questions:
Is there anyone around who is able to explain me the structure of a model
file or point to least some minimal documentation?. Why do nearly every
manual operations on a model in an editor destroy them, and how can I
avoid this?


Hi Bernd,

I would suggest building and saving a simple model with a Calculator 
included, and then removing it, saving a copy of the file, and looking 
at a diff between the before and after model files, that way you should 
get a better idea of the model file structure and hopefully some 
pointers to repairing your original model!


Cheers,

Andy

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Re: [Qgis-user] Small maths problem!

[Andrew Harfoot]

Just a thought Richard, but if you don't need to edit the data, could 
you not use a join to add a (precalculated) rotation field on the fly, 
either on the DB side, or in QGIS?


Cheers,

Andy

On 23/07/2015 09:10, Richard McDonnell wrote:

Hi,
I am in need of some guidance, I am trying to create an "active 
hatch/Fill" as part of a style im working on. What I want is for a 
hatch to rotate depending on the orientation of a Polygon.

For example, here is the same entity rotated, with the hatch rotating.


The issue is I am working on a database, onto which I cant add any 
data (additional columns) to the tables, I would like to do this from 
within the styling.
You can use an expression to denote the angle, so I was hoping to do 
it that way.
I was looking to utilize the geometry of a bounding box, and calculate 
the angle of the diagonal, using something like


180*atan((ymax - ymin)/(xmax - xmin))/$pi + 90

But I am not having any luckIf there is no way at present to do 
this, Might I put it forward as a possible new feature?


Regards,

Richard.



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Re: [Qgis-user] features disappearing when zoomed in

[Andrew Harfoot]

Have a look at this:

https://hub.qgis.org/issues/10098

If this is your problem, deleting the SBN/SBX files and / or building a 
QGIS spatial index (QIX) should help.


On 09/07/2015 00:38, Donovan Cameron wrote:

I've seen that happen when there's an invalid spatial index on the data.

Delete or rebuild the spatial index. Might help.




Donovan

On 08/07/15 02:24 PM, Luca Galuppini wrote:
i have this shapefile (a building shapefile, area type) that will 
disappear from view when zoomed in. it happens only in certain spots, 
and it works nice in others. of course the visibility based on scale 
is not set. is it a known bug, or it is my shapefile who is corrupted 
after so many passages and corrections in different softwares? how 
can i check out and fix it?





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Re: [Qgis-user] lat/log grid

[Andrew Harfoot]

Hi Brent,

The following a link from the page you originally referenced to the OGC 
MetOcean DWG there is a link to a GitHub repository with some symbols in 
SVG here:


https://github.com/OGCMetOceanDWG/WorldWeatherSymbols

Andy

On 04/02/2015 21:29, Brent Wood wrote:

Hi,

This symbol library seems something that I, & perhaps others, would 
find useful in QGIS.


Does anyone have any idea how this could be imported into QGIS?

http://blog.gvsig.org/2015/02/02/gvsig-2-1-symbol-libray-for-climatology/
Thanks,

   Brent Wood



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Re: [Qgis-user] Interpolation

[Andrew Harfoot]

Hi Michael,

Off the top of my head, but have you looked into a laser scanner mounted 
on some sort of aerial platform such as a cherry picker? Not sure 
whether the platform would be stable enough.


Alternatively a low level UAV flight may provide a detailed enough DTM 
through stereo imagery analysis.


Cheers,

Andy

On 18/09/2014 10:43, Michael.Dodd wrote:
Any suggestions as to the best way to survey and interpolate ridge and 
furrow grassland that is not on a flat plane?

I have tried various methods without success.

The ridge and furrow area that I want to map is about 120mx120m, the 
ridge and furrow pattern is distinct with about 0.5m or difference 
between ridge ht and furrow base but the pattern has a slight curve 
towards one end and the land is not flat.  If you are not sure what 
ridge and furrow looks like then there is an example at 51.9827, 
-0.9135, the stripes are clearly visible on the google earth image.


Mapping can be done with cm level dgps but does this require many tens 
of thousands of points to be recorded. Or can fewer points be recorded 
and qgis interpolation somehow be told to interpolate along the ridge 
and furrow then fill in the area between them with some sort of curve. 
The actual curve is also problematic as the ridge top tends to be 
flattened and not a smooth sine wave.  I don't have good LIDAR of the 
area but even that resolution may not be good enough.


-- The Open University is incorporated by Royal Charter (RC 000391), 
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Re: [Qgis-user] Four band raster displaying funny

[Andrew Harfoot]

Interesting!

Just found that you can override the GDAL behaviour of adding alpha 
interpretation (this is the default as described in the GTiff format 
spec here <http://www.gdal.org/frmt_gtiff.html>) by adding the GDAL -co 
command PHOTOMETRIC=RGB. Not sure how this tallys with the YCBCR colour 
model used by JPEG though?


Cheers,

Andy

On 02/12/2013 16:30, Jonathan Moules wrote:

Hi Andy,
I guess that makes sense.

Relating to gdalwarp:
- Output files by default are larger than gdal_merge.
- But they can be much smaller. You have to set *both*  -wm and 
--config GDAL_CACHEMAX - if you only set -wm, then the file is 
actually larger!
- gdal_merge seems to do something that results in some heavy blurring 
when using -co PHOTOMETRIC=YCBCR - this doesn't happen with gdalwarp.


So the optimal filesize for an aerial photograph is rendered with 
something like:


gdalwarp -of GTiff -wm  --config GDAL_CACHEMAX  -co
TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=80
-co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co PHOTOMETRIC=YCBCR
input1.tif input2.tif output.tif


I've not tried the four-band stuff again; just trying to optimise by 
3-band.


Thanks,
Jonathan


On 2 December 2013 16:10, Andrew Harfoot <mailto:a...@geodata.soton.ac.uk>> wrote:


I think QGIS is innocent in this - if a band is set as an alpha
channel then it should be handled as such by default in a viewer
(so mark down Arc for not using the alpha information!).

GDAL is the culprit as it is adding the alpha interpretation
without being prompted. I have just replicated this with some RGBI
imagery myself: prior to passing through GDAL's hands the IR band
is present, but isn't interpreted as an alpha channel. I can't get
the -setci switch to do anything though :(

Cheers,

Andy


On 02/12/2013 16:00, Jonathan Moules wrote:

Hi Andy,
Yep, that was it. I didn't know QGIS could do that; another good
example of software trying to be "smart" and confusing the poor
user. :-)



I didn't know gdalwarp could do mosaicing too. I'll have to test
it. I'll ask on the gdal list if I want to try the -setci parameter.

Many thanks!
Jonathan


On 2 December 2013 15:48, Andrew Harfoot
mailto:a...@geodata.soton.ac.uk>> wrote:

PS. gdalwarp offers more flexibility when mosaicing rasters,
and is better at memory management. I have just noticed that
in GDAL 1.10 and above there is an gdalwarp option -setci
that 'Sets the color interpretation of the bands of the
target dataset from the source dataset'. This could be used
to remove the assignment of the alpha channel to the IR band
on merging. Sadly there isn't an example of its usage!


Cheers,

Andy

On 02/12/2013 11:53, Jonathan Moules wrote:

Hi List,
I've got a 4 band raster aerial photography (RGBI) that
comprises lots of tiles. I've merged some of the tiles
together with:

gdal_merge -o 1.tif -of GTiff -co TILED=YES -co
BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co
BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt


But the resultant file looks funny in QGIS.
This is what the source file looks like (correct):
Inline images 1

This is what the merged file looks like (wrong):
Inline images 2

All the shadows are a whitey colour. This doesn't happen
with 3-band (RGB) images.
I've tried comparing individual bands; they all look
different in the 4-band.

However, if I open the four-band in ArcGIS, it looks fine
(both source and original).

Anyone know what's going on? Is it a QGIS bug or is it doing
something "smart"; I can't see anything odd going on with
symbology.

Thanks,
Jonathan

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Re: [Qgis-user] Four band raster displaying funny

[Andrew Harfoot]

I think QGIS is innocent in this - if a band is set as an alpha channel 
then it should be handled as such by default in a viewer (so mark down 
Arc for not using the alpha information!).


GDAL is the culprit as it is adding the alpha interpretation without 
being prompted. I have just replicated this with some RGBI imagery 
myself: prior to passing through GDAL's hands the IR band is present, 
but isn't interpreted as an alpha channel. I can't get the -setci switch 
to do anything though :(


Cheers,

Andy

On 02/12/2013 16:00, Jonathan Moules wrote:

Hi Andy,
Yep, that was it. I didn't know QGIS could do that; another good 
example of software trying to be "smart" and confusing the poor user. :-)




I didn't know gdalwarp could do mosaicing too. I'll have to test it. 
I'll ask on the gdal list if I want to try the -setci parameter.


Many thanks!
Jonathan


On 2 December 2013 15:48, Andrew Harfoot <mailto:a...@geodata.soton.ac.uk>> wrote:


PS. gdalwarp offers more flexibility when mosaicing rasters, and
is better at memory management. I have just noticed that in GDAL
1.10 and above there is an gdalwarp option -setci that 'Sets the
color interpretation of the bands of the target dataset from the
source dataset'. This could be used to remove the assignment of
the alpha channel to the IR band on merging. Sadly there isn't an
example of its usage!


Cheers,

Andy

On 02/12/2013 11:53, Jonathan Moules wrote:

Hi List,
I've got a 4 band raster aerial photography (RGBI) that comprises
lots of tiles. I've merged some of the tiles together with:

gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES
-co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co
BLOCKYSIZE=512 --optfile tiff_list.txt


But the resultant file looks funny in QGIS.
This is what the source file looks like (correct):
Inline images 1

This is what the merged file looks like (wrong):
Inline images 2

All the shadows are a whitey colour. This doesn't happen with
3-band (RGB) images.
I've tried comparing individual bands; they all look different in
the 4-band.

However, if I open the four-band in ArcGIS, it looks fine (both
source and original).

Anyone know what's going on? Is it a QGIS bug or is it doing
something "smart"; I can't see anything odd going on with symbology.

Thanks,
Jonathan

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Re: [Qgis-user] Four band raster displaying funny

[Andrew Harfoot]

  
  
PS. gdalwarp offers more flexibility
  when mosaicing rasters, and is better at memory management. I have
  just noticed that in GDAL 1.10 and above there is an gdalwarp
  option -setci that 'Sets the color interpretation of the bands of
  the target dataset from the source dataset'. This could be used to
  remove the assignment of the alpha channel to the IR band on
  merging. Sadly there isn't an example of its usage!
  
  Cheers,
  
  Andy
  
  On 02/12/2013 11:53, Jonathan Moules wrote:


  
  Hi List,
I've got a 4 band raster aerial photography (RGBI) that
  comprises lots of tiles. I've merged some of the tiles
  together with:


gdal_merge
  -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
  COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co
  BLOCKYSIZE=512 --optfile tiff_list.txt


But the resultant file looks funny in QGIS.
This is what the source file looks like (correct):




This is what the merged file looks like (wrong):




All the shadows are a whitey colour. This doesn't happen
  with 3-band (RGB) images.
I've tried comparing individual bands; they all look
  different in the 4-band.


However, if I open the four-band in ArcGIS, it looks fine
  (both source and original).


Anyone know what's going on? Is it a QGIS bug or is it
  doing something "smart"; I can't see anything odd going on
  with symbology.



Thanks,
Jonathan
  
  
  This
transmission is intended for the named addressee(s) only and may
contain sensitive or protectively marked material up to
RESTRICTED and should be handled accordingly. Unless you are the
named addressee (or authorised to receive it for the addressee)
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you have received this transmission in error please notify the
sender immediately. All email traffic sent to or from us,
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legislation.
  
  
  
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Re: [Qgis-user] Four band raster displaying funny

[Andrew Harfoot]

  
  
Hi Jonathan,
  
  Is it possible that QGIS is using the infrared band as an alpha
  channel? This might explain the whitening effect, especially in
  non-vegetated areas. I would check the Layer properties
  Transparency tab to see whether anything is set as the
  transparency band. If it is, you could override QGIS by setting a
  default style.
  
  Cheers,
  
  Andy
  
  On 02/12/2013 11:53, Jonathan Moules wrote:


  
  Hi List,
I've got a 4 band raster aerial photography (RGBI) that
  comprises lots of tiles. I've merged some of the tiles
  together with:


gdal_merge
  -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
  COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co
  BLOCKYSIZE=512 --optfile tiff_list.txt


But the resultant file looks funny in QGIS.
This is what the source file looks like (correct):




This is what the merged file looks like (wrong):




All the shadows are a whitey colour. This doesn't happen
  with 3-band (RGB) images.
I've tried comparing individual bands; they all look
  different in the 4-band.


However, if I open the four-band in ArcGIS, it looks fine
  (both source and original).


Anyone know what's going on? Is it a QGIS bug or is it
  doing something "smart"; I can't see anything odd going on
  with symbology.



Thanks,
Jonathan
  
  
  This
transmission is intended for the named addressee(s) only and may
contain sensitive or protectively marked material up to
RESTRICTED and should be handled accordingly. Unless you are the
named addressee (or authorised to receive it for the addressee)
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you have received this transmission in error please notify the
sender immediately. All email traffic sent to or from us,
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www.geodata.soton.ac.uk

  

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