Path distance tool: uphill path

Question

Hi,

I am new to ArcGIS and would really appreciate your help understanding how to work the Path Distance tool. I have read the documentation and thought that I understood how the vertical and horizontal factors work, but I was wrong.

I would like to calculate the distance for the shortest uphill path to a "source" for each point in the raster. That is, we can only move uphill or flat - we can not go downhill.

To do so, I'm using the Path Distance tool in the Spatial Analyst in ArcMap. Here are the parameters that I've been setting:

input raster: just a single point that i created in a shapefile - this is my "source" - the tiny blue dot on the image below

input cost raster: nothing

input surface raster: dem (the image is to the right, and the blue point is my "source")

horizontal factor parameters: binary horizontal factor; zero factor = 1; cut angle = 180 (i don't care about the horizontal factor, so I want it to be able to move as it wants)

vertical factor parameters:

input vertical raster: dem

vertical factor: binary

zero factor: 1

low cut angle: 0 (because I don't want it to be able to go downhill)

high cut angle: 90 (steep angle is not the problem, as long as we're going up)

When I run the tool, the output I get is not at all what I expect. I am attaching that here as well (to the left). I don't expect this symmetry, since the point is located on the slope. I expect all locations uphill of it to not have a path, so there shouldn't even be any distances.

Please help me understand what parameters I am setting wrong.

Any input is much appreciated!

Thanks a lot.

DanPatterson_Retired · Answer

Natalya...I presume that you have moved on from this, however, from the 10.3 help (as in 10.2), Understanding path distance analysis—Help | ArcGIS for Desktop  you indicate that you didn't use a cost raster.  This will have the affect of stating that there is absolutely no impedance to movement through space, regardless of terrain, slope (up or down) etc.  By doing that I don't think any of your other parameters matter since I am not sure whether the cost per cell would be 1 or 0.

I would assign some realistic costs to the surface based upon slope (see the diagrams in the link) and at least have a cost surface tht can be accumulated in a realistic fashion.  I would then try using the defaults to see what you get, then introduce your vertical factor, leaving the horizontal factor alone.  Should the results still not appear realistic, then the other parameters will have to be re-examined.

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