Why does my viewshed output have more rows than observer points?

TimDavid

I am trying to run a viewshed analysis using viewshed 2 in ArcMap10.7.1. I have multiple observer points and a DEM as the inputs, and I am using the OBSERVERS analysis type with the ORRT as output along with the viewshed raster itself. From all the help pages and ESRI documentation I have read, my understanding is that the number of rows in the output raster's attribute table should be determined by the number of observer points, but my output table has 11,925 rows and doesn't seem to match up with my observer points or ORRT at all, which means I can't get the raster to show me which cells are visible from which points. My ORRT looks correct, but the regions in that table also don't match anything in the raster output and they have a different number of rows.

I have tried running it with less observer points but no luck. I've attached screenshots of the first 25 rows or so of the raster output table and the accompanying ORRT. Any ideas?

XuguangWang

Hi Tim,

With the OBSERVERS analysis type, the output raster records the unique region ID's that are visible to any combinations of the input observation points. Since the number of possible combinations is large, there can be more rows in the output raster attribute table than the number of input observation points.

For example, with 2 input observation points (A and , there can be as much as 3 rows in the output raster attribute table (representing areas that are visible to observer A, to observer B, and to both observer A and B, respectively).

For each region on the output raster, the corresponding observer(s) info can be looked up from the output observer-region relationship table.

Thanks

Xuguang