[GRASS-user] v.what.rast with centroids

[Achim Kisseler]

Hi Dave,

what I did in this case, was, as you said, to convert the centroids to 
points and then run v.what.rast.

One possibility to get the information to your table:
1- Convert the polygons (the categories) to raster with r.to.vect.
2- Do a v.what.rast with this "raster-area" map.
3- Make a table update and use 2- for identifying the right items.

I hope you like it,
Achim

Am 10.06.2010 19:40, schrieb Dave Roberts:
> Friends,
>
> I have an vector area map with numerous polygons with centroids. When I do
>
> v.what.rast vector=A raster=B column=C
>
> It appears to run, but doesn't actually enter any data into column C in
> the associated table in Postgres. Reading the help file, I suspect this
> is because A is an area instead of a point map, but the areas do have
> centroids which I would expect v.what.rast to employ.
>
> I could import the centroids as a separate points map, but then they're
> not associated with the table in Postgres.
>
> What's considered best practices in associating polygon centroids with
> other rasters or vector areas?
>
> Thanks, Dave