topic Minimum Slope Raster in ArcGIS Spatial Analyst Questions

Minimum Slope Raster

NemiBhattarai — Sun, 10 Apr 2016 06:47:56 GMT

I'm not sure, do the slope tool in Spatial Analyst generate maximum slope raster comparing elevation with it neighbors?

If yes I need the exact opposite..

Is there any way to generate minimum slope raster?

Re: Minimum Slope Raster

DanPatterson_Retired — Sun, 10 Apr 2016 10:08:35 GMT

The tool delivers a slope which is a tad more convoluted, not maximum and not minimum Slope—Help | ArcGIS for Desktop You can see the derivation here How Slope works—Help | ArcGIS for Desktop If you can describe how you want your slope to be derived with respect to its neighbors then you can use a filter/window to start the math, much like they do with convolution filters for imaging Convolution function—Help | ArcGIS for Desktop

Re: Minimum Slope Raster

NemiBhattarai — Sun, 10 Apr 2016 10:28:53 GMT

Thank you. I'll give it a try

The Help says:

"Slope is the rate of maximum change in z-value from each cell."

What I want is algorithm for the rate of minimum change in z value from each cell... Is it Possible??

Re: Minimum Slope Raster

DanPatterson_Retired — Sun, 10 Apr 2016 10:46:07 GMT

the actual maximum slope is the maximum drop which is just dz/dx with respect to its 8 neighbours... it isn't directly implemented in Arc* ... you could derive your own. A statement of what you are trying to do might help with surrogate measures

Re: Minimum Slope Raster

NemiBhattarai — Sun, 10 Apr 2016 11:04:05 GMT

I am having trouble with derivation of these:

[dz/dx] = ((c + 2f + i) - (a + 2d + g) / (8 * x_cellsize)

[dz/dy] = ((g + 2h + i) - (a + 2b + c)) / (8 * y_cellsize)

Re: Minimum Slope Raster

DanPatterson_Retired — Sun, 10 Apr 2016 13:05:08 GMT

That is the equation that is used by the slope tool... you don't need to do anything... the slope wil 'automagically' be calculated using that equation. The reference to the link was for background information to show how slope is calculated from a 2nd degree finite difference difference. Further examples can be found in any elementary gis text.. eg. Princples of Geographic Information Systems, Burrough and McDonald, oxford, 2000 (pp 193- or any incarnation of that text by the principle author