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

GRASS GRASS user
1

Greetings

I have a raster layer and a vector point layer and I need to associate pixel values with points:
1- pixel values that are over points;
2- 3x3 pixel neighbor pixel values over a point.
Is this possible do to in a more automatic way than query each by each point?
Thanks
Regards
helena

2

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

··· 
-- 
Micha Silver
GIS Consultant, Arava Development Co.
[http://www.surfaces.co.il](http://www.surfaces.co.il)
3

Hi

I was thinking in something much simpler like just printing Pixel values next to Point ID.

I will give a try on your suggestions.
Thanks

2012/3/28 Micha Silver <micha@arava.co.il>

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](http://www.surfaces.co.il)
4

Once you’ve added columns for the pixell values to the point vector, then you can, of course, display those attributes on your map.

–
Micha Silver
052-366-5918

-----Original message-----

From: Helena Herrera helenaherrera1980@gmail.com
To: Micha Silver micha@arava.co.il
Cc: grass-user@lists.osgeo.org
Sent: Thu, 29 Mar 2012, 14:36:12 GMT+02:00
Subject: Re: [GRASS-user] How to retrieve raster pixel value over a vector point layer

Hi

I was thinking in something much simpler like just printing Pixel values next to Point ID.

I will give a try on your suggestions.
Thanks

2012/3/28 Micha Silver <micha@arava.co.il>

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](http://www.surfaces.co.il)

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