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As a followup to what both Jarlath & I have said about GCPs, some colleagues working in Hawaii and New Mexico have used corresponding recognizable features in Google Earth to pull Z values when GCPs have not been used. Cheers, Dave On Thu, Aug 2, 2018 at 11:38 AM, [log in to unmask] < [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. > > ------------------------------------------------------------------------- > This list (NEARC-L) is an unmoderated discussion list for all NEARC Users. > > If you no longer wish to receive e-mail from this list, you can remove > yourself by going to http://s.uconn.edu/nearcsubscribe. > -- Dave Tewksbury FAA Certified UAS Pilot GIS & Tech support Dept of Geosciences Hamilton College Clinton, NY 13323 USA ------------------------------------------------------------------------- This list (NEARC-L) is an unmoderated discussion list for all NEARC Users. If you no longer wish to receive e-mail from this list, you can remove yourself by going to http://s.uconn.edu/nearcsubscribe.