ambijat wrote:
No, Hamish,
This is not the case as I see it.
ok, sorry if I misunderstood. how do you get a political boundary
from SRTM data? by watershed? is knowing the "length" actually
important? could whatever you are looking at be answered instead
by a less problematic metric like area or proportion?
My fundamental method is as follows:
1. in a 3x3 matrix of neighbours analysis I want to fit in
one worthy formula.
2. For every such matrix there are going to be at least 3
non-zero values and 6 zero values.
so far sounds like a job for r.mfilter or r.mapcalc's neighbor
modifier,
3. as we know that c^2 = a^2 + b^2, i would be counting on
a = elevation difference between the two adjacent cells, and
b = 90 meters, which is the resolution of the cell.
ok. is the center cell always non-zero/null? (ie skip over those)
4. So, c values for each such set of two adjacent cells can
be calculated, and a sum of all such values which are actually
hypotenuse values would give me more accurate value of the total
length of the boundary.This is a kind of algorithm I have in mind. Anybody who can
translate into formula?
probably it would be r.mapcalc (incredibly versitile), but I
guess you could get a head start by multiplying a r.slope.aspect
slope map into the mix.
good luck,
Hamish