On 12/11/08 15:05, Nikos Alexandris wrote:
On Wed, 2008-11-12 at 14:44 +0100, Nikos Alexandris wrote:
On Wed, 2008-11-12 at 05:35 +0100, Nikos Alexandris wrote:
Why isn't the cat column starting from 1 after (v.)patching vector maps
(whose cat's start normally from 1)? Is it that my maps have somethig
wrong? Is there a specific reason?
Following up with a WORKING example using "v.patch -a"
g.copy vect=block_trier,blocks --o
# using -a flag
v.patch -a input="block_daun" output="blocks" --o
# head of blocks is what I expect: cat(s) start with 1 :-)
That is logical, as here you do not alter the first map.
db.select blocks | head -5
cat|AREA|PERIMETER|RAS2X2_|RAS2X2_ID|RAS2X2_NR|BLOCK|STAND|BEFL_DATUM|
BEFL_JAHR|QUALITAET|block_id
1|4000000|8000|13141|13140|2558_5524|trier|01.10.2006|19.06.2005|2005||1
2|4000000|8000|13308|13307|2552_5522|trier|01.10.2006|19.06.2005|2005||1
3|4000000|8000|13310|13309|2556_5522|trier|01.10.2006|19.06.2005|2005||1
4|4000000|8000|13311|13310|2558_5522|trier|01.10.2006|19.06.2005|2005||1
# clean I guess is necessary when features overlap eachother.
v.clean blocks tool=break,snap,rmdupl,rmdac thres=1,1,1 out=blocks_clean
My question(s) about why does "v.patch -e" remain :-)
There is a fundamental problem with '-a' if the cat numbers in the two
maps are overlapping, but the attributes linked to these overlapping
numbers are different in the two maps:
GRASS 7.0.svn (nc_spm_06):~ > v.category map1 option=print
1
2
2
GRASS 7.0.svn (nc_spm_06):~ > v.category map2 option=print
1
2
GRASS 7.0.svn (nc_spm_06):~ > v.patch -e in=map1,map2 out=result
GRASS 7.0.svn (nc_spm_06):~ > v.category result option=print
2
3
4
6
7
=>no ambiguities between cats, starts at 2, but that is not a problem as
such
GRASS 7.0.svn (nc_spm_06):~ > v.patch -a in=map2 out=map1 --overwrite
GRASS 7.0.svn (nc_spm_06):~ > v.category map1 option=print
1
2
3
1
2
=> ambiguities between cats
This creates the following problem:
GRASS 7.0.svn (nc_spm_06):~ > v.db.select map1
cat|test
1|one
2|two
3|three
GRASS 7.0.svn (nc_spm_06):~ > v.db.select map2
cat|test
1|ten
2|twenty
GRASS 7.0.svn (nc_spm_06):~ > v.patch -a in=map2 out=map1 --overwrite
GRASS 7.0.svn (nc_spm_06):~ > v.db.select map1 cat|test
1|one
2|two
3|three
=> attributes 'ten' and 'twenty from map are gone since key fields have
to be unique in attribute tables
So, unless you are sure that there are not overlapping cat's in the maps
you are planning to patch, steer away from '-a'.
Moritz
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