[GRASS-user] GRASS 6.4 How to extract point-values from multiple rasters

[Markus Metz]

On Sat, Apr 6, 2013 at 1:11 PM, Tim Michelsen
<timmichelsen at gmx-topmail.de> wrote:
>>>> I have to extract isolated value from several raster.
> Interestingly.
> Yesterday I had the same task to solve:
> have a vector with some sampling points and wanting to insert values
> from 2 raster layers to the table.
>
>>> The GRASS module r.what [0] extracts raster values at a
>>> given location. As input you need to give the name of the
>>> raster map and the coordinates as east,north
>>>
>>> [0] http://grass.osgeo.org/grass64/manuals/r.what.html
>>
>> note that r.what can take multiple rasters and multiple point-
>> values as input, all in one pass, to make a table.
> I do not understand why r.what should be of help here.

r.what would not help here, but for the original question because
there a vector map was not mentioned.
>
> r.what [1] just prints out.
> Isn't the right tool v.sample [2]?

r.what extracts values from one or more raster maps at locations given
by coordinates.

v.what.rast uploads raster values at positions of vector points to the table.

v.rast.stats calculates univariate statistics from a raster map based
on vector areas (polygons) and uploads statistics to new attribute
columns.

HTH,

Markus M


> But this tool works in a way the user would not expect it:
>
> Now, the problem is with v.sample:
> 1) it just accepts 1 input raster only.
> 2) it creates a new vector with a totally new table instead of updating
> the attribute table of the input vector with the raster values
>
> A note to 2): Such a procedure is implemented in v.rast.stats.
>
> What do the GRASS devs think about the items 1) & 2)?
> Is it a legitimate enhancement?
>
> Kind regards,
> Timmie
>
> [1] http://grass.osgeo.org/grass64/manuals/r.what.html
> [2] http://grass.osgeo.org/grass64/manuals/v.sample.html
> [3] http://grass.osgeo.org/grass64/manuals/v.rast.stats.html
>
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