We've noticed this with the "pro-sumer" drones. Unless you have ground control there is little you can do to get accurate elevations.
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Jarlath O’Neil-Dunne
University of Vermont | USDA Forest Service R&D
On 8/2/18, 11:38 AM, "Northeast Arc Users Group on behalf of [log in to unmask]" <[log in to unmask] on behalf of [log in to unmask]> wrote:
Hi,
Wondering if anyone can advise on a .las file that has been brought to me.
Positions taken by a Phantom 3 drone north of Beirut, Lebanon. So not a "real" .las file.
Photoscan software was used to export readings from the drone to an .las file. There are no classification, intenity, or other values.
Bringing them into ArcGIS, elevation readings on the point cloud range from negative 128.718 to positive 31.363.
Visualizing the point cloud, it looks good. In xy space, positions are correct; elevations are correct relative
to one another so I can generate a 3D surface that visually matches the reality of the area's topography.
A little reading up indicates the elevations are relative to the Home Point (RTH) recorded by the drone. So the negative
values are what the drone records below its 0, and the positive are what the drone records above its 0.
If the real true elevation of the drone's 0 point is, say 85 meters above MSL, is there an equation someone can share that will
convert the drone data to real elevation to generate a DEM for viewshed modelling? Is it possible?
I've had a couple other people who are much better at math than me take a look.
Stymied.
Thank you.
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