[Qgis-user] averaging raster grid

[M.E.Dodd]

See replies to each point:
"* Display the GRASS region - you should see the red rectangle - then 
verify that the vector and raster layers are within that region (again 
from their info tables)." 
Does the whole of each layer have to be within the red rectangle?  It certainly was not when I started as I had not considered this.  However in the large numbers of things I later tried I set the area of interest to be the whole world which did include all layers but still got same problems.  Setting this area is rather a pain using the current method of typing numbers into the boxes, it would be nicer to have the option of drawing the rectangle directly on the map.

"* In the Raster->Properties->Symbology, switch to a "pseudocolor" color 
ramp. (Maybe the whole range is being displayed as white, for some reason?" Don't think this is the problem as I tried altering various things and nothing made the map show up.

"* Are all the layers, raster and vector, in the same GRASS location and 
mapset?"  
This is what I thought was the problem but could not work out how to get them all into the same mapset, they (the vector and rasters) are in separate ones.

"* How big are the original tiffs. Maybe displaying all four at once is 
overloading the machine? It might be best to begin with just one, and a 
section of the vector grid that covers just that raster?" 
As I mentioned I have loaded up rather more data than this on other occasions but only in qgis since I had not tried the link with GRASS before.

-----Original Message-----
From: Micha Silver [mailto:micha at arava.co.il] 
Sent: 16 April 2010 19:44
To: M.E.Dodd
Cc: 'qgis-user at lists.osgeo.org'
Subject: Re: [Qgis-user] averaging raster grid

I can't see what might be causing these crashes. I guess it's back to 
basics:

* Did you have a look at the raster info (in GRASS Toolbox, go to the 
Browser tab and click on the problem raster). Can you check that the 
extents look right? And what range of values does it show?

* Display the GRASS region - you should see the red rectangle - then 
verify that the vector and raster layers are within that region (again 
from their info tables).

* In the Raster->Properties->Symbology, switch to a "pseudocolor" color 
ramp. (Maybe the whole range is being displayed as white, for some reason?

* Are all the layers, raster and vector, in the same GRASS location and 
mapset?

* How big are the original tiffs. Maybe displaying all four at once is 
overloading the machine? It might be best to begin with just one, and a 
section of the vector grid that covers just that raster?


Cheers,

Micha



M.E.Dodd wrote:

> Came in this morning and was just about to post back to list saying how everything was fixed and working.  But then started up qgis, did a file, 'open recent project' to load up yesterday's work and the raster layers did not show, they were listed with a cross by them but nothing on screen even though they were showing fine yesterday.  Have just checked back at the screen dump from yesterday to check I am not completely loosing my mind and indeed they were there and the maps showing up (http://www.amanita-photolibrary.co.uk/Untitled-2).png).  The vector layer was fine.
> So shut down qgis again and tried loading them one by one, they all loaded without a problem except they showed nothing on screen and the value tool suggests there is 'no data' when you move the mouse over where the map should be.  I've tried recreating the grass raster layers from the original raster layers in qgis and again the same problem, whereas all of this worked fine yesterday, indeed it still appears to work fine today:
> "
> r.in.gdal -o input=C:/Projects/cepaea_megalab/DEM/W020N40.DEM output=w020n40gn2
>
>
>
> Over-riding projection check 
>
>
>
>
>
>
> r.in.gdal complete. Raster map <w020n40gn2> created.
>
> Successfully finished
> "
> But when you try to view output nothing appears.  Coordinate reference system is correct and there is a large file with this name that has been generated in the 'cell' part of where it should be.  I have checked the properties and its not set to transparent (I'm clutching at straws now), its at the top of the list so should be on top of anything else
> http://www.amanita-photolibrary.co.uk/Untitled-3.png
> the mouse is over NW Africa which is the w020n40gn2 area so it shows up the 'no data' in the value tool, the other raster layers are qgis ones (I have switched off the qgis version of w020n40)
>
>
> -----Original Message-----
> From: Micha Silver [mailto:micha at arava.co.il] 
> Sent: 15 April 2010 19:02
> To: M.E.Dodd
> Subject: Re: [Qgis-user] averaging raster grid
>
> M.E.Dodd wrote:
>   
>> I am running the v.in.ogr.qgis again and left it much longer even 
>> after it said 100% and now notice that even after it gives 100% it 
>> then goes onto other stages after a long wait so it appears that I may 
>> not have been patient enough in the first place.  Perhaps a less 
>> confusing progress indicator would be helpful as the bar has been 
>> across to 100% several times now and the program is still running, no 
>> idea how long it will actually take.  Ah now it says successfully 
>> finished.
>>
>>     
> Good news.
>
> GRASS always creates topologically correct vectors. That's an important 
> feature for GIS, but a double edged sword since every import goes thru 
> this long procedure of checking topology and fixing problems. That's 
> probably what was happening.
>
> Post back to the list how everything goes...
>
>  
>
>   
>> Many thanks for all your help.  Will start the next stage and try to 
>> be more patient!
>>
>> Mike
>>
>>  
>>
>> ------------------------------------------------------------------------
>>     
>
>
>   


-- 
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il
 


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