I have a porblem concerning the transformation of lines into area. I have .e00 files which I have converted with avcimport. These vector files are only lines even if some of them should define an area (there is no PAT in the e00 file, only AAT). I've tried importing the vector lines as area boundaries but it dont work quite well, some area are not showing up and some other that shouldn't be areas but holes are created. Is there an easy way to transform those lines which are defining an area into a real area so I could build a raster map with these area showing up? I've tried v.digit and selecting an centroid. However, for some area with holes the holes are still defined as areas (if I import the lines as area boundaries) or the lines are not defined as boundaries so I've got a centroid outside an area (is there a way to change the line into a boundary other than v.type, using v.type transform the lines as boundaries for 2 areas, which is not my case).
On Thu, Dec 02, 2004 at 07:00:18PM -0500, Allard, Yannick (EXP) wrote:
Hi everyone,
I have a porblem concerning the transformation of lines into area. I have .e00 files which I have converted with avcimport. These vector files are only lines even if some of them should define an area (there is no PAT in the e00 file, only AAT). I've tried importing the vector lines as area boundaries but it dont work quite well, some area are not showing up and some other that shouldn't be areas but holes are created. Is there an easy way to transform those lines which are defining an area into a real area so I could build a raster map with these area showing up? I've tried v.digit and selecting an centroid. However, for some area with holes the holes are still defined as areas (if I import the lines as area boundaries) or the lines are not defined as boundaries so I've got a centroid outside an area (is there a way to change the line into a boundary other than v.type, using v.type transform the lines as boundaries for 2 areas, which is not my case).
I'm using Grass 5.7.0
Hi Yannick,
you may try 'v.in.e00' from GRASS 5.7-CVS. Probably also other problems may go away
with an update to current GRASS 5.7-CVS (e.g., small angles were fixed after 5.7.0 release
in v.in.ogr).
It sounds like you are trying to build "donut" areas, with an internal isle clipped out. The only way I have found so far to do this is to parse the output from v.build option=dump to identify the island polygons, update the attribute table with this information, and then run v.extract to select only the non-isle polygons. It would be nice if v.category had a option to not label holes in a larger polygon.
David
On Thursday, December 2, 2004, at 04:00 PM, Allard, Yannick (EXP) wrote:
Hi everyone,
I have a porblem concerning the transformation of lines into area. I have .e00 files which I have converted with avcimport. These vector files are only lines even if some of them should define an area (there is no PAT in the e00 file, only AAT). I've tried importing the vector lines as area boundaries but it dont work quite well, some area are not showing up and some other that shouldn't be areas but holes are created. Is there an easy way to transform those lines which are defining an area into a real area so I could build a raster map with these area showing up? I've tried v.digit and selecting an centroid. However, for some area with holes the holes are still defined as areas (if I import the lines as area boundaries) or the lines are not defined as boundaries so I've got a centroid outside an area (is there a way to change the line into a boundary other than v.type, using v.type transform the lines as boundaries for 2 areas, which is not my case).
> I have a porblem concerning the transformation of lines into area. I
> have .e00 files which I have converted with avcimport. These vector
> files are only lines even if some of them should define an area
> (there is no PAT in the e00 file, only AAT). I've tried importing
> the vector lines as area boundaries but it dont work quite well,
> some area are not showing up and some other that shouldn't be areas
> but holes are created. Is there an easy way to transform those lines
> which are defining an area into a real area so I could build a
> raster map with these area showing up? I've tried v.digit and
> selecting an centroid. However, for some area with holes the holes
> are still defined as areas (if I import the lines as area
> boundaries) or the lines are not defined as boundaries so I've got a
> centroid outside an area (is there a way to change the line into a
> boundary other than v.type, using v.type transform the lines as
> boundaries for 2 areas, which is not my case).
>
> I'm using Grass 5.7.0
It sounds like you are trying to build "donut" areas, with an internal
isle clipped out. The only way I have found so far to do this is to
parse the output from v.build option=dump to identify the island
polygons, update the attribute table with this information, and then
run v.extract to select only the non-isle polygons. It would be nice
if v.category had a option to not label holes in a larger polygon.
'v.extract -d' will get rid of internal islands. Also after
'v.category option=add' you might try 'v.extract list=1-1000000'
which can be useful to get rid of unused polygons.
'man v.category':
"EXAMPLES
...
4) Add categories/centroids to a vector map without categories
v.category in=wkt out=wktnew option=add
..."
maybe then use that result with v.overlay or v.select to add back in
holes you do want?
Tricky bit is when you have polygons within a hole, e.g. a polygon vector
of land which has a lake with an island in it.