[GRASS-user] Vector Overlay Issues

GRASS GRASS user
1

On Feb 13, 2008, at 11:50 PM, grass-user-request@lists.osgeo.org wrote:

Date: Wed, 13 Feb 2008 12:21:34 -0700
From: Eddie <eddie@mailforce.net>
Subject: Re: [GRASS-user] Vector Overlay Issues
To: grass-user@lists.osgeo.org
Message-ID: <1202930494.8372.4.camel@localhost>
Content-Type: text/plain

Someone sent me an E-mail regarding my use of HTML in the previous
message and I'm sorry about that. Always learning. Allow me to re-phrase
in plain text.

I have been struggling for quite some time trying to make a land use
vector map out of two separate vector maps. One is water and the other
is vegetation. Both only contain areas, and those areas which are active
are set to a single category value (1 for water, 2 for vegetation).
Islands are valid areas with no category id. I have tried the following
two approaches

v.patch input=water,vegetation out=landuse
v.overlay ainput=water atype=area binput=vegetation btype=area
output=landuse operator=or

to no avail. The results is always something bizarre that I haven't
quite figured out the meaning of. Certainly not what one would expect.
Both maps appear to be topographically correct. I have uploaded a
tar.bz2 of the project file at
(http://eddie.alcazarmountain.com/kootenay.tar.bz2). I removed all the
other map files leaving only the two vector maps and a region setting.
It is only about two megabytes. I am running {GRASS 6.2.1 (2006)} on
{Linux spica 2.6.23-gentoo-r6 #1 Mon Jan 28 11:06:48 MST 2008 x86_64
Mobile AMD Athlon(tm) 64 Processor 3000+ AuthenticAMD GNU/Linux}.

I'm not positive what kind of output you are hoping for, but it sounds like you should be using the *and* operator instead of the *or* operator. "And" does an intersection (normally what you want for a model like you describe), and "or" does a union.

Michael

2

It is the *or* operation I need. I want all areas of both vector files
to be in the new file. And any overlap to create new categories. I
should then be able use v.reclass based on the old a and b cat values to
consolidate the new categories that contain both, no?

On Thu, 2008-02-14 at 08:09 -0700, Michael Barton wrote:

I'm not positive what kind of output you are hoping for, but it
sounds like you should be using the *and* operator instead of the
*or* operator. "And" does an intersection (normally what you want for
a model like you describe), and "or" does a union.

Michael