Visibility analysis to determine VLOS for drone flight

Question

Hi. I am trying to determine areas to sample on a mountain region using a drone. One of the restrictions is that the drone must be within the visual line of sight (VLOS) of an observer, at all times, while flying. To determine which sites I can sample within the VLOS , I am using ArcMap Visibility analysis (3D Analyst tool) to create viewsheds from a few points on the mountain region.

I have access to the DEM and canopy height rasters of my area of interest, so I combined both rasters with "Plus" to create my input raster for the visibility analysis. My observer offset (offsetA) is set to my height (1.6m). For surface offset or target height (offsetB), I was going to put 50m, as this is approximately how high the drone will fly above ground, however I would need this to be 50m above the DEM (bare ground), not the DEM+canopy height which is the input raster of the visibility tool.

Any ideas how I can achieve this? Is there a different way to achieve the desired result? Thanks.

David_Brooks · Answer

@savanananah you're correct, but I thought you could swap the observer to be the drone, and then you're output viewshed would still be the same result, but you could define the observer by spot, and you'd see all the locations on the terrain where you'd potentially not see the drone. You could place a point every 10-20m or so along your flight route.

Another approach would be to use the exploratory analysis viewshed tools and try a view dome. You could then create a polygon surface that represents the flight plane of the drone, and then create a viewdome at each viewpoint. The plight pane polygon would then be colourised green and red according to which parts of the flight would lose visiblity.

savanananah · Answer

Hi David,

Thanks for your response!

If the observer locations are set to myself as the observer (not the drone) wouldn't using SPOT for drone elevation be incorrect? Since SPOT is "used to define the surface elevations for the observation points", then wouldn't SPOT set my elevation?

Basically, I am trying to determine, when standing at specific viewpoints, the areas on the mountain where the drone will be in my visual line of sight, while it is flying 50m above ground. In other words, "what can the observer (me) see from location X"?

David_Brooks · Answer

@savanananah you can use the SPOT field as a height variable instead of offsetb, and then input absolute heights for the drone. Are you running visibility analysis for a single point in the air, or are you looking to run it for every pixel of the terrain, and then see which pixels have 100% visibility counts? If the latter, you could use SPOT for elevation, and calculate it by using the extract values to points gp tool from the base DTM.

If for some reason SPOT doesn't work (check the guidance to be sure) then you can use Feature to 3D by attribute to convert the points to PointZ, and viewshed will work on those as absolute heights.