Hi,
I'm running grass5.0 on RH8 linux.
I'm extracting one county border from a vector of all counties for the state of New Jersey, USA.
I do this:
v.extract -n type=area list=ESS input=stco_CO output=essex.border new=1
but wind up with the polygon for MOR (see below cats).
here's part of the dig_cats file.
# 23 categories
Vector map: stco_CO
0.00 0.00 0.00 0.00
1:SUS
2:PAS
3:BER
4:WAR
5:MOR
6:ESS
7:HUD
...
When I do:
v.extract type=area list=6 input=stco_CO output=essex.border new=1
I get both ESS and SUS polygons combined in one vector. (As if I did list=1,6)
The vector map stco_CO was created with:
v.in.shape -o in=stco.shp out=stco_CO label=CO scale=24000
v.support map=stco_CO option=build
Is it me, or does v.extract have problems?
Thanks,
Phil
On Monday 10 March 2003 03:48 am, Philipp Molzer wrote:
Hi,
I'm running grass5.0 on RH8 linux.
I'm extracting one county border from a vector of all counties for the
state of New Jersey, USA.
I do this:
v.extract -n type=area list=ESS input=stco_CO output=essex.border new=1
but wind up with the polygon for MOR (see below cats).
here's part of the dig_cats file.
# 23 categories
Vector map: stco_CO
0.00 0.00 0.00 0.00
1:SUS
2:PAS
3:BER
4:WAR
5:MOR
6:ESS
7:HUD
...
There is a bug in v.extract for '-n' option. It uses index instead of
category!!! For example for dig_cats
1:A
10:B
and list=A,B you get cat list 0,1. So your output is 'correct'
( 5(MOR) instead of 6(ESS) ) 
I disabled '-n' option 3 months ago (after 5.0.0 release).
This is the most interesting bug I have ever found in GRASS,
output is obviously wrong and the module is there for years
(1.0 10/01/89 mentioned in code).
Conclusion: It is not so important how the program works
as we can see on other popular SW.
Try to make the project with MOR instead of ESS and I think
that there is a good chance that nobody other will notice that.
When I do:
v.extract type=area list=6 input=stco_CO output=essex.border new=1
I get both ESS and SUS polygons combined in one vector. (As if I did
list=1,6)
This seems to be another bug. Did you check if cats are realy correct
in the input (d.what.vect)? Then we can narrow it to either v.extract or
v.in.shape.
The vector map stco_CO was created with:
v.in.shape -o in=stco.shp out=stco_CO label=CO scale=24000
v.support map=stco_CO option=build
Is it me, or does v.extract have problems?
Radim