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I'm in the process of performing a visibility analysis using the Visibility tool in ArcGIS Pro 3.0, but something is confusing me about the SPOT parameter. On the ArcGIS Pro website (https://pro.arcgis.com/en/pro-app/2.8/tool-reference/3d-analyst/using-viewshed-and-observer-points-for-visibility.htm) it says that the SPOT is "used to define the surface elevations for the observation points". If I'm using a DEM for my elevation surface, I would assume the SPOT would be the DEM value at my observer point. This fits with the description in this video (https://www.youtube.com/watch?v=q6i9yVm5lsI&t=108s&ab_channel=GIS-Toolstounderstandtheworld) which uses the diagram below. You can see that the SPOT is the height of the terrain under the observer point.

enter image description here

What I find confusing is that on the ArcGIS Pro website, it provides the figure below which shows the SPOT extending up to a horizontal plane above the observer point. Shouldn't the SPOT value be the height of that brown hill that the observer is standing on, or am I misunderstanding something?

enter image description here

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I think it's a poor illustration, but the Esri figure actually seems to be showing the same as the NTNU figure, notice the SPOT line intersects with a dashed line that looks like it would intersect the horizon plane

enter image description here

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    Yea I think you're right, the line you highlighted green is probably the SPOT elevation, it's just drawn in a very confusing way
    – Morgan
    Oct 9, 2022 at 21:21
  • Yes, very confusing. The NNTU one is so much clearer.
    – user2856
    Oct 10, 2022 at 0:32

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