topic Geodesic Viewshed Newbie - Observer Elevation, Observer Offset, Surface Offset Q's in ArcGIS Spatial Analyst Questions

Geodesic Viewshed Newbie - Observer Elevation, Observer Offset, Surface Offset Q's

BECK_K — Mon, 28 Aug 2023 19:18:38 GMT

Hi I'm a viewshed newbie. I am working on a tower sighting project that requires me to find areas in my raster that are visible from a person's average height of 6' in my input road network (observer dataset). I am assuming the 85' towers could be in any raster cell for this purpose. For the input raster I created a normalized digital surface model. In the dropdown of this tool (observer parameters), I specify 6' in observer offset and left observer elevation blank assuming it can get elevation from the input raster. I placed 85' in the surface offset. The results showed me that all areas within my raster were visible by at least one observer. That didn't seem correct.

I then tried adding fields to my observer dataset (OFFSETA and OFFSETB) instead of populating in the tool. From the guidance, I see OFFSETA is the height of the observer so I'm assuming that's where the 6' goes and OFFSETB would be 85'. That doesn't look correct either. It seems to have been more selective (instead of selecting all areas), but when compared to the first viewshed I ran without the 85' added to the raster cells, it's less area and not more. I would expect to see more areas if the towers were an added 85' not less. Any guidance would be appreciated if I'm not thinking of this correctly. Thank you!

Re: Geodesic Viewshed Newbie - Observer Elevation, Observer Offset, Surface Offset Q's

DanPatterson — Mon, 28 Aug 2023 19:57:23 GMT

These topics?

Using Viewshed and Observer Points for visibility analysis—ArcGIS Pro | Documentation

How Line Of Sight works—ArcGIS Pro | Documentation

Visibility (Spatial Analyst)—ArcGIS Pro | Documentation

Geodesic Viewshed (Spatial Analyst)—ArcGIS Pro | Documentation

Re: Geodesic Viewshed Newbie - Observer Elevation, Observer Offset, Surface Offset Q's

BECK_K — Mon, 28 Aug 2023 20:36:18 GMT

Thank you for the links. I had checked through those in my research and still had the questions above. The geodesic viewshed seemed to be the best tool for the job, but adding the 85' threw off the results a bit. Any other ideas or suggestions are welcomed!