Re: [Qgis-user] digitizing

[Patrick Dunford via Qgis-user]

There are some times when the libraries can run out of memory if a 
raster is very large, so you can have something that something like a 
graphics editor e.g Gimp can open OK but Qgis coujld have trouble 
opening it.


On 17/06/22 14:22, Firstname Lastname wrote:
I think that there is something wrong with the Tif file I was using.  
I had the same problem with a couple of files but I went back to the 
source file and redid the referencing and it is ok.


On Thu, Jun 16, 2022 at 7:46 PM Patrick Dunford via Qgis-user 
 wrote:


This is a generic answer, as more information would be needed to
determine exactly the situation you are experiencing.

If you zoom to the layer, is it then displayed in the same place
as the rest of your map?

My recollection of the georeferencer is it produces a world file
to go with the layer. This should have the correct top-left
coordinates and pixel resolution in it. Is there also an XML file
that specifies the CRS?

Look at the layer name where it is loaded in the GIS and see if
there is a question mark displayed next to its name, that
indicates QGIS doesn't have enough information to position the
layer, such as the information that is stored in sidecar files.

It is also possible if the file is very large that it will be slow
to display. Also have a look at the error log at the bottom of the
screen to see if any error messages are displayed.

On 17/06/22 04:23, Firstname Lastname via Qgis-user wrote:

i have been successfully using the georeferencer for some time. 
i referenced several maps and they succesfully georeferenced
and  displayed for me.
Then, i was digitizing and i ran the georeference tool and for
some reason, the new referenced maps do not display.  i have
exited and tried to georef in a new project and made sure that i
have the same CRS for the basemap and the georef tool but when i
run the referencer, the layer appear but the map will not
display.  i have tried restarting, clearing the georef tool and
running again but i get the same result.   Does anyone know what
i am doing wrong and why my referenced maps will not display?

-- 
Byron Veilleux, MSc. P.Geo

Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414

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Re: [Qgis-user] most efficient way to digitize polygons

[Thayer Young via Qgis-user]

 Hi Byron,
  I recommend making one large polygon and then using the Split Features tool 
to cut individual polygons out of the original polygon. Just remember to select 
the polygon that you want to split before using the tool, and start and finish 
the split line on the outside of the polygon.  This effectively eliminates 
topological errors between the adjacent polygons. Which means that there will 
not be any gaps or overlaps between them, since the splitting process will 
generate duplicate points in each polygon for every mouse click along the split 
path.
  The only disadvantage is that you will have to manually go back and fill in 
the attributes for each polygon. Know that the new polygon that is split from 
the original will inherit the attributes of the original.
  If you need to adjust boundaries later, you should use the Snapping Toolbar, 
specifically enable Snapping and enable Topological Editing. When polygons 
share points, if you move a point it will move all polygons that share that 
point.

-Thayer


On Thursday, June 16, 2022 at 03:00:38 PM EDT, 
qgis-user-requ...@lists.osgeo.org  wrote:  
 
Date: Thu, 16 Jun 2022 09:26:32 -0600
From: Firstname Lastname 
To: Qgis-user@lists.osgeo.org
Subject: [Qgis-user] most efficient way to digitize polygons
Message-ID:
    
Content-Type: text/plain; charset="utf-8"

i am a qgis newby and i am beginning a large project that involves
digitizing several geology maps.  i am trying to determine the best way to
manage the digitizing and avoid extra work.
my question to the group is:  If i have several coloured polygons that are
adjacent to each other, is there an efficient way to digitize one polygon
and then use one edge of that polygon for the adjacent polygon so that i
dont have to redigitize the same edge twice and so that i will have
precisely overrlapping polys with no gaps?  should i digitize one polygon,
export and rename it?  can i digitize one have of the next polygon and
somehow merge it with the now re-imported polygon?
is there a more efficient way to do this?

many thanks

-- 
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
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Re: [Qgis-user] digitizing

[Firstname Lastname via Qgis-user]

I think that there is something wrong with the Tif file I was using.  I had
the same problem with a couple of files but I went back to the source file
and redid the referencing and it is ok.

On Thu, Jun 16, 2022 at 7:46 PM Patrick Dunford via Qgis-user <
qgis-user@lists.osgeo.org> wrote:

> This is a generic answer, as more information would be needed to determine
> exactly the situation you are experiencing.
>
> If you zoom to the layer, is it then displayed in the same place as the
> rest of your map?
>
> My recollection of the georeferencer is it produces a world file to go
> with the layer. This should have the correct top-left coordinates and pixel
> resolution in it. Is there also an XML file that specifies the CRS?
>
> Look at the layer name where it is loaded in the GIS and see if there is a
> question mark displayed next to its name, that indicates QGIS doesn't have
> enough information to position the layer, such as the information that is
> stored in sidecar files.
>
> It is also possible if the file is very large that it will be slow to
> display. Also have a look at the error log at the bottom of the screen to
> see if any error messages are displayed.
> On 17/06/22 04:23, Firstname Lastname via Qgis-user wrote:
>
> i have been successfully using the georeferencer for some time.  i
> referenced several maps and they succesfully georeferenced and  displayed
> for me.
> Then, i was digitizing and i ran the georeference tool and for some
> reason, the new referenced maps do not display.  i have exited and tried to
> georef in a new project and made sure that i have the same CRS for the
> basemap and the georef tool but when i run the referencer, the layer appear
> but the map will not display.  i have tried restarting, clearing the georef
> tool and running again but i get the same result.   Does anyone know what i
> am doing wrong and why my referenced maps will not display?
>
> --
> Byron Veilleux, MSc. P.Geo
> Conjugate Geologic Services Limited
> Calgary, Alberta Canada
> by...@conjugategeo.com
> Cell:4037108414
>
> ___
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-- 
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414
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Re: [Qgis-user] digitizing

[Patrick Dunford via Qgis-user]

This is a generic answer, as more information would be needed to 
determine exactly the situation you are experiencing.


If you zoom to the layer, is it then displayed in the same place as the 
rest of your map?


My recollection of the georeferencer is it produces a world file to go 
with the layer. This should have the correct top-left coordinates and 
pixel resolution in it. Is there also an XML file that specifies the CRS?


Look at the layer name where it is loaded in the GIS and see if there is 
a question mark displayed next to its name, that indicates QGIS doesn't 
have enough information to position the layer, such as the information 
that is stored in sidecar files.


It is also possible if the file is very large that it will be slow to 
display. Also have a look at the error log at the bottom of the screen 
to see if any error messages are displayed.


On 17/06/22 04:23, Firstname Lastname via Qgis-user wrote:
i have been successfully using the georeferencer for some time.  i 
referenced several maps and they succesfully georeferenced 
and  displayed for me.
Then, i was digitizing and i ran the georeference tool and for some 
reason, the new referenced maps do not display.  i have exited and 
tried to georef in a new project and made sure that i have the same 
CRS for the basemap and the georef tool but when i run the referencer, 
the layer appear but the map will not display.  i have tried 
restarting, clearing the georef tool and running again but i get the 
same result.  Does anyone know what i am doing wrong and why my 
referenced maps will not display?


--
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414

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Re: [Qgis-user] most efficient way to digitize polygons

[Nicolas Cadieux via Qgis-user]

Hi,

Depending on what you are doing and what kind of results you are looking 
for, could you simply use "Polygonize" and then clean those results.  If 
your map are in RGB only, you could do a raster classification analysis 
before hand.  Line would follow pixels at first but those could be fixed 
using various vector tools.


Just a thought!

Nicolas

On 2022-06-16 11:26 a.m., Firstname Lastname via Qgis-user wrote:
i am a qgis newby and i am beginning a large project that involves 
digitizing several geology maps.  i am trying to determine the best 
way to manage the digitizing and avoid extra work.
my question to the group is:  If i have several coloured polygons that 
are adjacent to each other, is there an efficient way to digitize one 
polygon and then use one edge of that polygon for the adjacent polygon 
so that i dont have to redigitize the same edge twice and so that i 
will have precisely overrlapping polys with no gaps?  should i 
digitize one polygon, export and rename it?  can i digitize one have 
of the next polygon and somehow merge it with the now re-imported 
polygon?

is there a more efficient way to do this?

many thanks

--
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com


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Re: [Qgis-user] digitizing

[Nicolas Cadieux via Qgis-user]

Hi,

Look's like there's a problem with the georeferenced layer or perhaps 
the CRS or the coordinates of the base map.


The first thing would be to look at the layer CRS to see if it's good.  
Then, right click on that layer in the layer panel, go to Layer CRS and 
then select "Set Project CRS from layer.", then zoom to the layer.  I 
would look at the coordinates to see if they are valid.  Then, I would 
open the base map and check the same things.  I would also try to use a 
web mapping service site google earth to see if you base map is in the 
right place.  Perhaps the base map CRS is problematic.


That would be my starting point for trouble shooting.

Nicolas

On 2022-06-16 12:23 p.m., Firstname Lastname via Qgis-user wrote:
i have been successfully using the georeferencer for some time.  i 
referenced several maps and they succesfully georeferenced 
and  displayed for me.
Then, i was digitizing and i ran the georeference tool and for some 
reason, the new referenced maps do not display.  i have exited and 
tried to georef in a new project and made sure that i have the same 
CRS for the basemap and the georef tool but when i run the referencer, 
the layer appear but the map will not display.  i have tried 
restarting, clearing the georef tool and running again but i get the 
same result.  Does anyone know what i am doing wrong and why my 
referenced maps will not display?


--
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414

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https://gitlab.com/njacadieux
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[Qgis-user] digitizing

[Firstname Lastname via Qgis-user]

i have been successfully using the georeferencer for some time.  i
referenced several maps and they succesfully georeferenced and  displayed
for me.
Then, i was digitizing and i ran the georeference tool and for some reason,
the new referenced maps do not display.  i have exited and tried to georef
in a new project and made sure that i have the same CRS for the basemap and
the georef tool but when i run the referencer, the layer appear but the map
will not display.  i have tried restarting, clearing the georef tool and
running again but i get the same result.   Does anyone know what i am doing
wrong and why my referenced maps will not display?

-- 
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414
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Re: [Qgis-user] i would like my basemap to display UTM and LAt long grid lines

[Randal Hale via Qgis-user]

Once you start building a layout add your map frame. Make sure it's 
selected and to the right you should see the item properties panel for 
the frame. Scroll down and you'll see "grid" - that will let you add a 
grid with a different crs and different style of grids and tics. 
Disclaimer - I've overly simplified this explanation so spend some time 
playing around with the options.


Randy

On 6/16/22 11:48, Firstname Lastname via Qgis-user wrote:
i am using a NAD 83 UTM grid for my basemap and want to display 
lat-long grid on this as well, does anyone know how i can do this in QGIS?


--
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414

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-
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[Qgis-user] i would like my basemap to display UTM and LAt long grid lines

[Firstname Lastname via Qgis-user]

i am using a NAD 83 UTM grid for my basemap and want to display lat-long
grid on this as well, does anyone know how i can do this in QGIS?

-- 
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
Cell:4037108414
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Re: [Qgis-user] most efficient way to digitize polygons

[chris hermansen via Qgis-user]

Byron and list,

On Thu, Jun 16, 2022 at 8:26 AM Firstname Lastname via Qgis-user <
qgis-user@lists.osgeo.org> wrote:

> i am a qgis newby and i am beginning a large project that involves
> digitizing several geology maps.  i am trying to determine the best way to
> manage the digitizing and avoid extra work.
> my question to the group is:  If i have several coloured polygons that are
> adjacent to each other, is there an efficient way to digitize one polygon
> and then use one edge of that polygon for the adjacent polygon so that i
> dont have to redigitize the same edge twice and so that i will have
> precisely overrlapping polys with no gaps?  should i digitize one polygon,
> export and rename it?  can i digitize one have of the next polygon and
> somehow merge it with the now re-imported polygon?
> is there a more efficient way to do this?
>
> You may wish to read one or more of the available tutorials on the topic
of digitizing in QGIS.

For example, this one:

https://www.qgistutorials.com/en/docs/3/digitizing_basics.html

where you would pay particular attention to steps 22 through 26 where
snapping new polygons to existing ones is demonstrated.


-- 
Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
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[Qgis-user] most efficient way to digitize polygons

[Firstname Lastname via Qgis-user]

i am a qgis newby and i am beginning a large project that involves
digitizing several geology maps.  i am trying to determine the best way to
manage the digitizing and avoid extra work.
my question to the group is:  If i have several coloured polygons that are
adjacent to each other, is there an efficient way to digitize one polygon
and then use one edge of that polygon for the adjacent polygon so that i
dont have to redigitize the same edge twice and so that i will have
precisely overrlapping polys with no gaps?  should i digitize one polygon,
export and rename it?  can i digitize one have of the next polygon and
somehow merge it with the now re-imported polygon?
is there a more efficient way to do this?

many thanks

-- 
Byron Veilleux, MSc. P.Geo
Conjugate Geologic Services Limited
Calgary, Alberta Canada
by...@conjugategeo.com
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[Qgis-user] New Density Analyses Plugin

[C Hamilton via Qgis-user]

I want to share a new vector based density analysis plugin sooner rather
than later. My work priorities are being rearranged so that I will not be
able to do new development or new features, but only fix bugs if they
arise. Here is the new plugin. Please test it out and give me any feedback.
I have about a month where I can optimize it more, but after that I will
not be able to do further development.

https://plugins.qgis.org/plugins/densityanalysis/

You can read the Density Analyses Documentation
,
but here are the highlights.

This plugin currently has 3 vector based density algorithms:

   1. *Create density map grid* - This one creates a grid of polygons and
   counts the number of points in those polygons using the QGIS *Create
   grid* processing algorithm followed by the *Count points in polygon* and
   then styled appropriately. It is very important that the input point data
   be spatially indexed. This algorithm provides the most flexibility,
but *Count
   points in polygon* is time consuming.
   2. *Create geohash density map* - This makes use of the geohash
   algorithm to geohash each point and count the number of points for each
   geohash and create the geohash polygons. Depending on the density of the
   map this can be an order of magnitude faster than the above algorithm. The
   disadvantage is that you are limited to the geohash grid resolutions.
   3. *Create H3 density map* - This is the fastest of all 3 algorithms. It
   creates a hexagon density map grid and is similar in that it uses a H3
   geohash index to count all the points in each geohash. Unfortunately, H3 is
   not a part of the QGIS standard python libraries and you will need to 'pip
   install h3' to be able to access these algorithms, but it will be worth it.
   QGIS developers, you may want to consider including H3 as a part of QGIS.

Here are some running times of the 3 algorithms with a data set of around
194,000 points.

   - Create density map grid - 63.18 seconds
   - Create geohash density map - 5.6 seconds
   - Create H3 density map - 3.7 seconds

Once the heatmaps are created (note that they are automatically styled),
then there is a heatmap explorer that allows you to load in the N highest
grid counts and by clicking on them it will pan or zoom to the heatmap
polygon to examine the data that is there.

There are also 3 other utilities.

   1. *Apply style to selected layers* - You can copy a style to the
   clipboard or select a .qml file and apply it to all selected layers or
   groups of layers.
   2. *Apply graduated style* - This applies a graduated style to a layer,
   but it is done as a processing algorithm so it can be used in the model
   builder.
   3. *Apply random categorized style* - This applies a random categorized
   style to a layer, but it is done as a processing algorithm so it can be
   used in the model builder.

I plan on also adding a raster based polygon density algorithm that seems
to be missing from QGIS.

If you have any suggestions or find any problems with the plugin please let
me know.

Thanks,

C. Hamilton
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