[GRASS-user] v.dissolve with singleparts?

Uwe Fischer gisfisch at t-online.de
Tue Apr 13 05:21:42 PDT 2021

Hello list,


I would like to write centroid coordinates to a GRASS map table and export
them along with one item (attribute) to CSV for further use outside GRASS.


But v.to.db option=coor will no write all my coordinates. That is obviously
because the map was created using dissolve, and the dissolve item (let’s
call it >owner<) is sometimes duplicate in spatially distinct areas. One
owner – many distinct areas. The dissolve process wrote duplicate CAT values
in these cases, and v.to.db does not like those duplicates, so it will not
write coordinates. Maybe all the areas of one owner are linked to one
database record to represent them als multiparts. If this is the case, it
would be very smart if GRASS would ask (while dissolving) if the user wants
multiparts or not.


Now I wonder how to overcome this. I tried to write new centroids to a
second layer with new unique CATs (v.category option=add layer=2 and so on),
but this layer has lost the owner item. I have no idea how to link back to
the item because the link number CAT is new. 


v.reclass also did not help me, because there is no item to base a
reclassification on. Owner is duplicate as well as CAT is duplicate.


What is the best way to do this? Thanks for help.


Mit freundlichen Grüßen,

Uwe Fischer


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