[GRASS5] attributes using v.overlay
otto.dassau at gmx.de
Mon Sep 6 11:13:26 EDT 2004
I used the module v.overlay with operator "or" -> union, but I guess it`s the same for all operators. I have following problems with the attributes.
v.overlay ainput=area1 binput=area2 output=area3 operator=or
the attribute table for area3 looks like this:
cat | cata | catb
1 | 2 | 4
2 | 4 | 7
AFAICS these columns can be connected to the attribute tables from ainput and binput using different fields.
It seems that this is not done automatically, because in file
vectors/area3/dbln only one link to column "cat" is set
-> 1 area3 cat $GISDBASE/$LOCATION_NAME/$MAPSET/dbf/ dbf
anyway now I can add further links to the other attribute tables via fields manually or by using v.db.connect
-> 2 area1 cat $GISDBASE/$LOCATION_NAME/$MAPSET/dbf/ dbf
-> 3 area2 cat $GISDBASE/$LOCATION_NAME/$MAPSET/dbf/ dbf
When I now query the map I get all attributes from the two maps I overlayed (unioned) before - this is nice and the result I was expecting.
Now my questions:
a) Why are the two attribute tables of the input maps area1 and area2 not automatically linked in vectors/area3/dbln?
b) How is it possible to query two attributes represented by different fields? E.g. show all areas where area1 connected through field 2 has value 1 and area2 connected through field 3 has value 2.
c) When I remove the overlayed map area3, also the basemaps area1 and area2 are deleted, which is really bad :-(. How can I prevent this without removing the "dbln" entries?
thanks a lot
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