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 _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
