[GRASSLIST:7622] Re: surface interpolation

[Paul Kelly]

Hello Maciek

Maciek Sieczka wrote:
> Although the vector engine of Grass 5 is much worse than in 6, v.patch 
> plays
> the role fine there, being able to populate attributes from input to output
> properly.

I'm not sure I agree; can you explain in more detail? As I understand it 
the 5.4 v.digit is as simple as the 6.0 version. (the following 
discussion may be confusing as I use the terms categories and attributes 
as they apply in GRASS <= 5.4; it may or may not be different in >= 
5.7). Each element in the map has an associated category number---the 
dig_att file associates the geometry elements with the category numbers, 
and the dig_cats file associates the category numbers with the attribute 
values.

If elements in the two different vector maps being patched have the same 
category numbers but those category numbers have different attribute 
values (either strings or decimal numbers) associated with them in each 
map (i.e. the two maps have different dig_cats files), then the 
attribute values in the second map are lost and those from the first map 
are used in the output map. So v.patch does nothing to avoid category 
number clashes between the two maps.
As I understand it. Haven't worked with this for a while though.

Paul