[GRASS-user] DEM Import - lost elevation data

rchirgwin at ozemail.com.au rchirgwin at ozemail.com.au
Mon Aug 27 06:13:27 EDT 2007


I feel a forehead-slapping moment coming on... to see if I get this:
1) Import DEM (say, East Coast of Australia) to new location creates a 
region with the extents of the DEM.
2) Import second DEM which is outside the region of the first DEM = null 
values *because* it's outside the original extents.

I think I'm with you ... tomorrow I will try your suggestions. Many 
thanks, as always!

Richard Chirgwin

Hamish wrote:
> Richard Chirgwin wrote:
>> I have imported models from srtm.csi.cgiar.org, using ASCII downloads. 
>> To import the models, I'm using r.in.gdal.
>> If I import the model to a new location, everything looks fine, and if I 
>> query the imported map, I get results that make sense. For eg:
>> r.what -f input=testdem at PERMANENT east_north=151.3524554,-30.85835173
>> returns:
>> 151.3524554 -30.85835173 1026
>> (I have taken out the | delimiters to make it more legible)
>> But if I then import a different DEM tile from the same site, in the 
>> same format, and load it into the same location, it loads without the 
>> elevation. Hence:
>> r.what -f input=DEM2 at PERMANENT east_north=119.2521986,-30.56112713
>> returns results like:
>> 119.2521986 -30.56112713 *
>> If I load the second DEM into a new location, it will work fine but no 
>> other DEMs will show their elevation data.
>> Can anyone provide suggestions as to the likely cause?
> "*" as a value indicates that the value of that cell is NULL. One
> possible/ probable reason for that is if the map is outside of the
> current region. Anything off the end of the map will be reported as NULL.
> That's the raw value of the data, nothing to do with color settings,
> those are applied later.
> try  "g.region -p rast=DEM2" to set the current region to the map's
> extents. Also,
>   g.region -p rast=DEM1,DEM2
> will zoom to a region which covers both maps.
> guessed,
> Hamish

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