[GRASSLIST:4407] Re: v.patch problems
paul-grass at stjohnspoint.co.uk
Thu Sep 23 17:46:38 EDT 2004
On Wed, 22 Sep 2004, Carlos Henrique Grohmann wrote:
> Hello all,
> I'm trying to patch some vector maps in GRASS 5.3, but there are problems. the
> maps are contours and spot heights in shape format. when I import then,
> everything is OK, the contours have the right z-value, and so the points (in
> vector format). the problem is when I try to patch them, and the final result
> comes with completely different z-values. all labels are changed.
> any ideas?
v.patch is a simple algorithm and assumes the attribute numbers correspond
to the same category labels (I presume you have the z co-ordinates as
category labels) in all the input maps. If they don't then the output
will be mixed up.
If your z values are all integers greater than 0 then you can make the
attribute number be the actual z value and don't have any category labels.
You should be able to achieve this with careful use of the command-line
parameters to v.in.shape I think.
If you have 0, negative or decimal values I suppose you could multiply
them by something and add a bit on to make them positive integers, or make
sure all your attribute numbers occupy different ranges in all the inputs
maps or something (no idea how to do that). I've run into this problem
lots of times and it is very awkward. I think I worked around it just by
giving every line in each map a different attribute number. That is very
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