I have merged three CORINE vector maps for coniferous, broad-leaved and
mixed forests in order to create one general map for all forests as I need
to calculate the length of the forest edges.
After using v.patch (with flag e) to merge the maps I have tried my best to
remove all lines lying inside of boundaries so that only the outer
boundaries would be left - with no luck. The main problem should be that the
adjacent boundaries from the three maps have only been put next to another
and not really "merged" (this is not a problem concerning double
boundaries). Does anyone know how to cope with this? I have not been able to
find any posts regarding this problem and would really appreciate your help.
I am working with GRASS 6.4.0+42329 (2010) on Ubuntu
I have merged three CORINE vector maps for coniferous, broad-leaved and
mixed forests in order to create one general map for all forests as I
need to calculate the length of the forest edges.
the problem is fractal and has no answer. you need to think of a way to
work by area, or if you can absolutely confirm the coverage is digitized
at the same scale throughout (almost all are not, even if all the digitizing
was done by the same person for the same project), you could work with
relative proportions.
lots of software and people will give you numbers for the question, but
really that number doesn't mean much at all (unless you are a pure
mathematician). defining margins is a tricky business..
"[Mandelbrot's] discussion implies that it is meaningless to talk about
the length of a coastline; some other means of quantifying coastlines are
needed."
(we should make this a FAQ...)
After using v.patch (with flag e) to merge the maps I have tried my
best to remove all lines lying inside of boundaries so that only
the outer boundaries would be left - with no luck. The main problem
should be that the adjacent boundaries from the three maps have only
been put next to another and not really "merged" (this is not a problem
concerning double boundaries). Does anyone know how to cope with this?
try the v.dissolve module. note that works on map features with categories,
and boundaries often do not have category numbers by default, so you'll
have to deal with that first (v.category).
On Wed, Jun 22, 2011 at 7:32 PM, puffbunnyn <arne.kaldhusdal@gmail.com> wrote:
Hello
I have merged three CORINE vector maps for coniferous, broad-leaved and
mixed forests in order to create one general map for all forests as I need
to calculate the length of the forest edges.
After using v.patch (with flag e) to merge the maps I have tried my best to
remove all lines lying inside of boundaries so that only the outer
boundaries would be left - with no luck. The main problem should be that the
adjacent boundaries from the three maps have only been put next to another
and not really "merged" (this is not a problem concerning double
boundaries). Does anyone know how to cope with this? I have not been able to
find any posts regarding this problem and would really appreciate your help.
When patching areas, a bit of cleaning is needed before anything else
can be done.
Try
v.clean tool=bpol,rmdupl
if there are any incorrect boundaries or duplicate centroids left, try
v.clean tool=break,rmdupl,rmsa
repeat this until tool=rmsa makes no modifications
If you want to remove the inner boundaries, you could prepare the
vector for v.dissolve with
v.category op=del cat=-1
followed by
v.category op=add cat=1 step=0 type=centroid
Now all areas have the same category and you can use v.dissolve or
v.extract -d to remove the inner boundaries.