Visibility takes the same time for 360 degrees and 90 degrees

Question

I am doing Visibility on some DTM.

My first test was on 360 degrees. I set the extent to the extent of the circle. It took 3:45 minutes.

Then I did it second time from 0-90 degrees. I set the extent to quarter of the previous extent.

I was waiting for about 25% of the time or a little above.

Instead I get 90% of the time (about 3:20)

How is this possible?

mody_buchbinder · Answer

Hi Dan

The geodesic Viewshed required vertical spatial reference.

My data is on a "general" sphere and in UTM SR. I am not sure what is the correct vertical sr here.

My observer is in memory but I do not know about any way to save the result raster in memory.

Thanks

DanPatterson · Answer

Geodesic Viewshed (3D Analyst)—ArcGIS Pro | Documentation

purports to provide enhanced and/or faster performance.

Does it return the same results? and is the timing similar?

I suspect that visibility performs the calculation on the whole (eg 360) then does a final slicing of the result.

You could try to see if using "memory" workspace does the same thing which would rule out writing to disk as a possible reason