Calculate the height of vertical DEM areas

Question

Hi,

is there a way to calculate the height of the vertical (or almost vertical) areas in a DEM?

I need it to determine the resistance of the terrain for the dispersal of tortoises. As tortoises are able to cope with some step heights but limited as soon as a certain value is reached, the vertical features can be crucial for the fragmentation of a terrain (from a tortoise point of view 
).

Many thanks in advance for any ideas & inputs,

Annette

DanPatterson_Retired · Answer

This is a bit out of the box, but you can convert a raster to a numpy array which makes the task a bit easier >>> import numpy as np >>> a = np.ones((4,5),dtype=int) >>> b = np.ones((4,5), dtype=int)*5 >>> >>> # This is a constructed 'cliff' >>> >>> cliff = np.c_[(a,b)] >>> cliff array([[1, 1, 1, 1, 1, 5, 5, 5, 5, 5], [1, 1, 1, 1, 1, 5, 5, 5, 5, 5], [1, 1, 1, 1, 1, 5, 5, 5, 5, 5], [1, 1, 1, 1, 1, 5, 5, 5, 5, 5]]) >>> >>> np.diff(cliff) array([[0, 0, 0, 0, 4, 0, 0, 0, 0], [0, 0, 0, 0, 4, 0, 0, 0, 0], [0, 0, 0, 0, 4, 0, 0, 0, 0], [0, 0, 0, 0, 4, 0, 0, 0, 0]]) >>> >>> # note that the elevation and its value are readily visible >>> >>> # a different cliff >>> a = np.arange(10).reshape(5,2) >>> b = a[::-1] >>> cliff = np.c_[(a,b)] >>> >>> cliff array([[0, 1, 8, 9], [2, 3, 6, 7], [4, 5, 4, 5], [6, 7, 2, 3], [8, 9, 0, 1]]) >>> np.diff(cliff) array([[ 1, 7, 1], [ 1, 3, 1], [ 1, -1, 1], [ 1, -5, 1], [ 1, -9, 1]]) >>> np.abs(np.diff(cliff)) # now take the abs if direction is to be removed array([[1, 7, 1], [1, 3, 1], [1, 1, 1], [1, 5, 1], [1, 9, 1]]) >>> ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ you can mess around with the concepts. In the above examples, a first order difference is obtained between adjoining raster cells. Slope sort of does this, but with numpy arrays, you can really play with the outputs. and decide what you consider a threshold value for a 'cliff'. If you need to return an array of the exact size, this can also be accomplished, but it is basically a small detail. So once you have decided on you approach, you can examine the 'slope' and/or 'curvature' functions built within arcmap itself which can be used to a similar affect if you don't want to go to rastertonumpyarray then numpyarraytoraster for the conversions.