Re: [GRASS-user] How to retrieve raster pixel value over a vector point layer

Wed, 28 Mar 2012 12:07:12 -0700

On 03/28/2012 08:11 PM, Helena Herrera wrote:
Greetings
 
I have a raster layer and a vector point layer and I need to associate pixel values with points:

When you say "associate" If you mean to add the raster values to a column in the point vector attribute table, then v.what.rast is what you're looking for.

1- pixel values that are over points;
2- 3x3 pixel neighbor pixel values over a point.

Create a new raster with r.neighbors then run v.what.rast again to upload these 3x3 neighborhood values to another column in the point vector.

Is this possible do to in a more automatic way than query each by each point?

Here are the steps:
v.db.addcol vector_map col="rast_val double, rast_val_3x3 double"
v.what.rast vector_map rast=raster_map col=rast_val
r.neighbors raster_map out=raster_map_3x3  # assumes averaging a 3x3 window
v.what.rast vector_map rast=raster_map_3x3 col=rast_val_3x3

Thanks
Regards
helena

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-- 
Micha Silver
GIS Consultant, Arava Development Co.
http://www.surfaces.co.il
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