Hello
I am trying to determine the height of slopes from the actual toe to the crest, without having to digitize the toe and crest. I'm not being lazy - the area of interest is large and it will be very time-consuming to do the latter. In essence, I am hoping there is a method in Spatial Analyst / 3D Analyst or a formula that I can use in Raster Calculator.
Do you already have the crests and toes extracted?
How many of those slope "lines" should be created?
Should the length show the length using the surface or a straight line?
Hi Xander,
I don't have the toes and crests extracted as yet.
The client wants to see the height of the slope as contours / colour grid ranging from 0m to ± 300m in 50m intervals. The length should be the actual height of the slope and not the values of the surface elevation
Hi Ansu Louw ,
I'm afraid I'm a bit lost in the explanation... When you refer to the "actual height of the slope", are you referring to the elevation or the length of the slope?
For what I understand you are not interested in the length of the brown line following the surface, but in the slope length, right? ... and you want to generate contours in a 50 m interval based on the length of the slope... If so, that will probably be a very complicated process and include some heavy coding (even if you would already have lines representing crests and toes)...
Hi Xander,
Yes that is correct. I want the actual slope length (perhaps height is not the right wording).
If I were to simplify it and try obtain the length of the "brown line" what would you suggest?
Thanks for the additional explanation. To determine the slope length using the actual surface doesn't make things easier. I would probably apply some of the code used for this solution: Re: Creating a surface buffer? .
However, If you are more interested in the straight slope length between crest and toe, than the straight line would make it less complex. Now the idea of creating contours that represent an equal slope length, makes things ever more complex. It would require to create multiple slope lines (many), determine points on these lines and the interval mentioned (50m) and connect these to form lines (and determine if the interval should start on the crest or the toe). Additionally mountains should be isolated for this process. Sounds like a very interesting problem, but pretty complex...
As I said... pretty complex..., but not impossible...
You will have to digitize the toe and crest since a slope value only applies for a very small 3x3 window so all you could do is figure out the length by considering the slope value and aspect at a cell. This would give you the ability to get an estimate of the surface length for the window...but consider that the slope derived for one cell is not know by its adjacent cells. You task would be to make these cells self-aware.
Consider the following example:
So the questions become:
You can easily do this in your head...can't you? The task becomes translating your 'rules' to those that can be implemented in raster and/or vector world. So some discussion of your criteria, would be useful. Are you only interested in
Interesting problem, there are some things that could be done, but rather than throwing tools at a problem and hoping a solution arises, formulate the required steps to see if the solution is realizable without human intervention.
mmm, just wondering... I remember that your friend William Huber did some magic in Avenue to detect crests...
Would it be possible to generalize the aspect of the surface using the SciPy circular mean (scipy.stats.morestats.circmean(numpy_raster)) as Shaun Walbridge showed in his presentation at the DevSummit this year (Python: Working With Scientific Data ) and using a moving window to detect opposite aspect angle ranges to depict crests and toes (won't work with rather flat and wide valleys)?
mmm... I think this is the (ancient) thread I was talking about Finding peaks from a DEM where William Huber collaborated.
I will have a look through Bill's links later, but I do remember him doing something like this and curvature is coming to mind, but don't quote me. Some of my concerns in my original post still haven't be answered as yet even if the surface length is still being sought after. Contour lines would help IFFF they are at least representative of the underlying DEM, you can atleast propagate normal lines etc. I will have a look, just trying to finish up some einsum stuff