Add Surface Information Tool - How does it really (exactly) calculate values for a line segment?

Question

Hi,
My name is Klemen.
I use the tool Add Surface Information quite a lot.
I usually use raster surface (1x1 Meter) to get the surface information for road network. I use for example 10-Meters (or 50-Meters, or different length) road segments.
I use the bilinear interpolation method as this is the only option.
As a result I get the information for Z_Min, Z-Max, Z_Mean, SLength, Min_Slope, Max_Slope and Avg_Slope.
But I really wonder, how these parameters are calculated. I would really appreciate to have one example (with illustration/picture) how for example Z-Max, Min_Slope and Avg_Slope for certain line-segment are calculated.
Thank you very much and king regards!
Klemen

KlemenPrah1 · Answer

Hi again. I have read your post. Yes, I have similar problem and question.

Besides, there is mentioned a bilinear interpolation which is the only possible option to choose when working with raster surface. I understand the principle of bilinear interpolation in general, but how it works on the example of "Add Surface Information" or "Interpolate Shape", on the case of line object, I couldn't explain exactly.

Kind regards, Klemen

MerylK · Answer

I have a similar question as Klemen that the Surface Parameters tool does not quite address. My overall goal is to be able to visualize slope along a trail alignment so that it can be designed to stay under 10 degrees. My current workflow consists of running Modify-Divide, selecting equal intervals which results in approximately 15ft segments, then running Add Surface Information and symbolizing by Average Slope. The issue is I'm not entirely sure how that Average Slope is being calculated. The documentation says "Average slope is obtained by weighing each slope by its 3D length, then determining the average. This results in longer segments having greater influence on the resulting value over shorter segments." But what does it mean by segment? Is that the Sampling Distance parameter? Or is it the segments of the line I've divided the trail into? Either way each length would be almost identical. What I need it to do is calculate the slope across the entire line segment  since we don't care if there is 1ft of steep terrain. Please provide more clarification on how this tool works and if you are unable they do you have any suggestions for an improved workflow?

GISMallku · Answer

I can't speak to the Add Surface Information tool (I'm not on the software development team) but I do know that there is an improved tool called Surface Parameters in ArcGIS Pro 2.7: https://pro.arcgis.com/en/pro-app/latest/tool-reference/spatial-analyst/surface-parameters.htm  And that comes with How Surface Parameters works—ArcGIS Pro | Documentation which describes specifics.

Much of the How To info was also published in this blog in February: Improved Terrain Analysis Algorithms in ArcGIS Pro 2.7

I hope that this helps.