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
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
_______________________________________________
Qgis-user mailing list
Qgis-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/qgis-user
