Hi All,
I'm trying to use v.what.rast to find out the value of cells in a raster
map at the coordinates of shapes in a vector file (using grass5.7 cvs)
A couple of problems I'm having are:
1. How do I create a new column in a table within a dbf file? Is it
possible through GRASS? Or should I just use a seperate tool?
2. I've tried just overwriting the category( "cat" ) column but nothing happens:
1284 categories loaded from table
0 categories loaded from vector
0 categories from vector missing in table
0 duplicate categories in vector
0 records updated
0 update errors
Is this because v.what.rast is limited to only points? If so, can anyone
suggest a way of either converting shapes to sets of points, or calculating
the number of cells of each type under a shape?
Thanks for your time,
Joel
On Wednesday 06 October 2004 05:07, Joel Peter William Pitt wrote:
Hi All,
I'm trying to use v.what.rast to find out the value of cells in a raster
map at the coordinates of shapes in a vector file (using grass5.7 cvs)
A couple of problems I'm having are:
1. How do I create a new column in a table within a dbf file? Is it
possible through GRASS? Or should I just use a seperate tool?
echo "alter table xxx add column yyy double precision" | db.execute
2. I've tried just overwriting the category( "cat" ) column but nothing
happens:
1284 categories loaded from table
0 categories loaded from vector
0 categories from vector missing in table
0 duplicate categories in vector
0 records updated
0 update errors
Is this because v.what.rast is limited to only points?
Yes.
If so, can anyone
suggest a way of either converting shapes to sets of points, or calculating
the number of cells of each type under a shape?
Thanks for your time,
Lines and polygons usually cover many different values so v.what.rast
does not make sense. You can overlay 2 rasters.
Radim