This question seeks to clarify a point made in an answer to ArcGIS Viewshed without Observer Points, which states:

I'm fairly sure that the number of points [Viewshed] generates along the line depends on the DEM resolution; for example, if you've got a 100m line and a raster with 10m cells, your line will be analyzed as 10 points.

Can anyone confirm this is true in ArcGIS Pro? I have a DEM raster of 30-meter cell size, and a polyline observer feature that is quite long (a 463 kilometer boundary line to be precise.) I'm getting a maximum of 279 observers. When you work out the math that would mean ≤2% of the boundary can "see" any given cell. It seems too low.

(Specifically I'm looking to convert the number of observers into the percentage of the boundary.)

  • 1
    Have you reviewed Using Viewshed and Observer Points for visibility analysis and other ArcGIS Pro help pages about the Viewshed tool and Viewshed function? – PolyGeo Nov 19 '20 at 1:47
  • @PolyGeo I had, but apparently missed this useful bit: "When polyline input is used, every node and vertex along each input arc is processed as an individual observation point." Now I suppose I just need to determine how to count the number of nodes and vertices. – D. Betchkal Nov 19 '20 at 1:54

One (awkward) answer:

When using polyline inputs to the Viewshed tool, one can use arcpy.management.FeatureVerticesToPoints("polyline feature", "output point feature", "ALL") to convert every vertex to a point. Then the length of the attribute table provides the number of observer points.

In the case of this question, it gives a much more reasonable value of 957 observers. Or, the most visible cell in the DEM raster was visible from ≤29% of observer points.

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