[GRASS5] anyone use/need fragstats?
blazek at itc.it
Thu Jun 19 04:43:43 EDT 2003
On Wednesday 18 June 2003 18:47, John Gillette wrote:
> I have a question about:
> > v.patch input=a,b output=c1
> > v.clean input=c1 output=c2 tool=break,rmdupl
> Given: ___
> _________ | |
> | A | | |
> | | | |
> |_________| | B |
> patch A,B gives:
> | A| | | ?
> | | | |
> | B |
> There are 4 intersections and 5 areas created
> by the patch operation in this example. What does
> "v.clean input=c1 output=c2 tool=break,rmdupl"
> do to patch's result?
v.clean breaks boundaries on intersections so that c2
realy contains 5 areas.
> I am interested in a v.mapcalc that would do A union B,
v.extract input=c4 output=x where="a is not null or b is not null"
> A intersection B,
v.extract input=c4 output=x where="a is not null and b is not null"
v.extract input=c4 output=x where="a is not null and b is null"
v.extract input=c4 output=x where="a is null and b is not null"
> as well as Booleans like
> is_simple(A), is_convex(A).
> Are there library functions
> for doing such things in 5.1? I suspect that we are not
> quite there yet?
There are no such functions. I want only to remind, that such functions
working on 2 areas only, are useless in GRASS. Function overlaying
2 vectors must work on 2 complete input vector layers and produce new
> Actually, I am more interested in having the library functions
> than having v.mapcalc.
> Could you tell me what you are working on with respect
> to these kinds of problems and what your plans are?
Currently I am doing nothing for this. For future, there
are 2 options, I think,
1) develop these functions in GRASS
2) get rid of topological model (i.e. 5.1) and use GEOS
> Ref: general polygon clipper library (gpc)
> CGAL, the Computational Geometry Algorithms Library
> CGAL Basic Library Manuals, Polygon Operations
Maybe better (in this context): http://geos.refractions.net/
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