[GRASS-user] How to get perimeter?

[Hamish]

Margherita Di Leo wrote:
> I'm searching for a way to delineate the perimeter of an
> area in a raster map. The area is like the result of
> r.clump, so it is caracterized by a integer number in the
> raster map. I have no problem in trasforming the raster map
> in vector with r.to.vect, but the vector is an area, not a
> line. I need to know the lenght of the contour of the areas.
> What is the best way to obtain that?


beware the dreaded fractal coastline problem.

especially if you are working with a raster map which is likely
to have saw-tooth edges.

it is better to compare areas. you might be able to compare perimeter
length as a ratio of other clumps on the same map, but that's about it.

http://en.wikipedia.org/wiki/How_Long_Is_the_Coast_of_Britain%3F_Statistical_Self-Similarity_and_Fractional_Dimension


Hamish