[GRASS-user] Length of a political boundary

[Hamish]

ambijat wrote:
> I have a typical problem. I have extracted the raster
> boundary line from SRTM data. each cell contains the
> elevation value. Idealll\y speaking the total length of a
> boundary would be the some of the cells x cell resolution
> (90m). But, this is not true to actual boundary length as
> there are elevation in mountainous regions.
> 
> So, I need to add all the hypotenuse values of the cells.
> How can it be done any idea ?

you can do lots of refinement, but fundamentally it's a fractal problem
with no real answer,
see
http://en.wikipedia.org/wiki/How_Long_Is_the_Coast_of_Britain%3F_Statistical_Self-Similarity_and_Fractional_Dimension

the 2D plan-area within a boundary will converge on a single answer though
as you make dx smaller and smaller. also within a single constant dataset
you can compare one area to another ("this edge is x% of the total
boundary").

v.to.rast + v.to.db may give you an answer, but I won't use it.


see also the r.surf.area and r.volume modules, which are slightly different
creatures in the same family of problem.


Hamish