M.E.Dodd wrote:
Am still trying this. Seems I might be nearly there but for some reason can't
create a grass vector layer so can't use the v.rast.stats command.
I have created the grass raster layers from the raster layers that are open in
qgis and they seem fine but when I try to create the grass vector layer it says
its worked but then won't visualise it. to summarise this part I have an open
vector layer in qgis, also saved as a shapefile, when I run the command to
convert this layer to a grass vector layer there are not errors but it won't
visualise when the command completes and I can't add it as a new grass layer
even though it says it recognises the filename.
Hi Mike:
(I'm assuming that the vector and raster are projected in the same CRS,
and they overlap.)
Can you open the GRASS toolbox and switch to the Browser tab. Then open
the vector section, and click on this imported vector. On the right you
should see a table similar to below.
Please either post a screen shot on the web somewhere, or you can
copy/paste the text into a mail message. Send this to the qgis-user
maillist and we can try to understand what is wrong.
While you're at it, grab the same table of info for the raster, and post
that as well...
Vector
veg
Points
0
Lines
0
Boundaries
5732
Centroids
835
Areas
4293
Islands
3516
North
55:51:56.766357N
South
39:35:35.604858N
East
30E
West
12:35:51.329041E
3D
no
History
COMMAND: v.in.ogr -o
dsn="/home/micha/geodata/Training/Geodata/vector/VMAP0/veg_cropland.shp"
output="veg" min_area=0.0001 snap=-1
GISDBASE: /home/micha/geodata/grass
LOCATION: WGS84 MAPSET: PERMANENT USER: micha DATE: Wed Apr 14 22:21:18 2010
------------------------------------------------------------------------
802 input polygonsTotal area: 1.053955e+12 (4293 areas)Overlapping area:
7.020819e+09 (53 areas)Area without category: 1.341091e+11 (3458 areas)
--
Micha
Am wondering if this is some kind of bug since the structure of ht eprogram
seems to be just the same for the raster and vector but the raster works but
the vector does not.
-----Original Message-----
From: Micha Silver [mailto:mi...@arava.co.il]
Sent: 14 April 2010 11:28
To: M.E.Dodd
Cc: Qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] averaging raster grid
On 14/04/2010 13:25, M.E.Dodd wrote:
Yep just after emailing I got it into grass and am now fighting with the
v.rast.stats command which at the moment is not accepting the layers I want to
use with it, will look at the manual. Thanks for your help as I had not got
into the GRASS link in qgis before as each time I had tried it previously it
broke.
Be sure you have created the GRASS Location correctly (choose the same
Coordinate System as your original data). It's easy when using the QGIS
wizard.
-----Original Message-----
From: Micha Silver [mailto:mi...@arava.co.il]
Sent: 14 April 2010 11:22
To: M.E.Dodd
Cc: Qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] averaging raster grid
On 14/04/2010 13:06, M.E.Dodd wrote:
I've uninstalled qgis and reinstalled it using the OSGeo4W installer and got
GRASS too. However when I come to use the GRASS plugin I can't see how to get
to v.rast.stats infact it does not really want to know since the maps are in
qgis not as GRASS maps.
Yes, GRASS uses its own internal data format. So you need to import the
raster and vector into GRASS with the commands:
v.in.ogr dsn=<path to shapefile> out=vect_grid
r.in.gdal<path to raster> out=rast_name
Then try v.rast.stats
I recommend the QGIS user's manual to better understand these procedures.
http://download.osgeo.org/qgis/doc/manual/qgis-1.4.0_user_guide_en.pdf
especially the chapter on GRASS
-----Original Message-----
From: Micha Silver [mailto:mi...@arava.co.il]
Sent: 13 April 2010 18:18
To: M.E.Dodd
Subject: Re: [Qgis-user] averaging raster grid
M.E.Dodd wrote:
Thanks for both replies. Will try to send new fresh messages in future, I did
not know about the issue you mention.
I don't have the GRASS plugin, do you need to have GRASS installed as well as
qgis to use this (I don't have GRASS installed). From what you say then this is
just what I want v.rast.stats
What operating system? How did you install?
On windows, if you used the OSGeo4W installer (recommended) then you can
rerun the installer, choose the "Advanced" installation method, then
check to install GRASS. (Also choose the "unstable" QGIS version 1.4
There's also a ready made Windows package with GRASS here:
http://kcubeconsulting.com/download.php
On Ubuntu there are ready made packages in the UbuntuGIS repository.
One other issue on the plugins, today when I have been using qgis the list of
possible plugins is rather shorter than normal as if something strange has
happened to it, all the normal plugins I use and are installed are there but
the longer list of ones that are not installed all seem to have vanished (I
often browse this list to see if there is anything that might be useful but
they have gone).
Don't know about that. Did you click the "Fetch Python plugins"? and did
it go to the internet to refresh the list of available plugins?
-----Original Message-----
From: Micha Silver [mailto:mi...@arava.co.il]
Sent: 13 April 2010 15:46
To: M.E.Dodd
Subject: Re: [Qgis-user] averaging raster grid
On 13/04/2010 16:58, M.E.Dodd wrote:
I have a raster digital elevation model and want to overlay a coarser grid
vector layer and average the very detailed raster to give the average values in
each of the grid squares specified by the vector grid, is this possible? The
existing vector and raster tools hint at doing some of it but I can't work out
how to do exactly this.
Hi Mike:
You might not be aware the mail list keeps messages "threaded", so if
you reply to a message, but change the subject, your new message still
gets stuck into the ongoing thread of the original, making things hard
to follow. If you have a new subject, send a new message, not a reply.
As to your question:
I gather that your vector "grid" is a polygon layer of rectangles? Using
the GRASS plugin you can run the module called v.rast.stats. This module
calculates univariate statistics from a raster layer for each polygon in
a vector layer, and adds the stats to new columns in the vectors
attribute table.
Does that help?
Regards,
Micha
Mike
--
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il
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