The short story: Is there a way to "rescue" islands from vector areas? In other words, "break" the area up? This is hard for me to put into words, so I've drawn a picture to help explain what I want to do:
The long story: I know it isn't topologically correct to do this. The problem is that I'm exporting this data as a shapefile for use in another program -- and that program doesn't understand "rings" in shapefiles! It sees all rings as outer rings, and doesn't understand holes. The only way to make this program see the existence of the hole would be to break up the polygon as in the diagram above so that it can be represented with one simple outer ring. I don't need the data to be modeled this way inside GRASS, just in the exported shapefile (or any other format that I could then translate into a shapefile).
Aside: I know the proper solution would of course be to add outer/inner ring support to this external program, but unfortunately that's not an option. It's a kludge, but it's the only way I can think of to get valid data into this program!
Many thanks,
--
David Norris
danorris@ncsa.uiuc.edu
The short story: Is there a way to "rescue" islands from vector areas?
In other words, "break" the area up? This is hard for me to put into
words, so I've drawn a picture to help explain what I want to do:
Maybe edit your vector in v.digit/QGIS GRASS Edit, connecting the inner
and outer boundary with a line (propably without a category)? GRASS
accepts that. Look for the "bridge" idea in v.clean manual.
The short story: Is there a way to "rescue" islands from vector areas?
In other words, "break" the area up? This is hard for me to put into
words, so I've drawn a picture to help explain what I want to do:
The long story: I know it isn't topologically correct to do this. The
problem is that I'm exporting this data as a shapefile for use in
another program -- and that program doesn't understand "rings" in
shapefiles! It sees all rings as outer rings, and doesn't understand
holes. The only way to make this program see the existence of the hole
would be to break up the polygon as in the diagram above so that it can
be represented with one simple outer ring. I don't need the data to be
modeled this way inside GRASS, just in the exported shapefile (or any
other format that I could then translate into a shapefile).
Aside: I know the proper solution would of course be to add outer/inner
ring support to this external program, but unfortunately that's not an
option. It's a kludge, but it's the only way I can think of to get valid
data into this program!
