I’m experimenting with using a drone to gather aerial photos. The program I’ve been using has the capability of exporting a few different products. The basic DEM and photo rasters are awesome and I’m fine working with them but I have a few questions.
The DEM elevations are relative, and I don’t really know what units they are in or what they are relative too. Is there any way to change all of the DEM values based on a few known elevations, using bench marks or lidar data?
The program I’m using also exports a 3D product that is an .obj file type. Is it worth the hassle of trying to get a .obj into ArcScene? If I wanted to do something 3D would I be better off starting with the DEM and messing around with the tools Esri provides. (3D stuff is way out of my comfort zone, but it makes a fun visual)
I use a couple of different drones for work- a fixed wing and a rotary.
My software does work with ground control, as has some of the other software I’ve used. I use professional-grade survey software though. I’ve not used any ESRI software for the 3D elevation fixing, but…
If you have map algebra components for your ArcMap (Spatial Analyst extension) you could certainly move the elevation values to match a known position- just add/subtract the needed amount to the raster cell values of your DEM so that the elevations are more in line with the known elevation of an included point on the DEM. This won’t rubber-sheet, so if your elevations are wonky across the whole model, a different approach would be needed, as all cells will change simultaneously.
I use Map Algebra to fix my DEMs because my clients faint at seeing metric elevation readouts, so I convert my rasters directly to US Survey Feet.
What software are you using for your post-flight processing, if you don’t mind me asking?
I’m using a the basic version of dronedeploy. If you know of something better I’m game but price is a bit of an issue.
I guess I was overthinking this whole thing. Your answer is simple and straightforward. If my drone sets the elevation of the takeoff point as 0, I just need to add the actual elevation to all of the values.
As far as the 3D issue goes. I discovered dronedeploy will also export a .las? point cloud instead of the obj. Esri seems to like the point cloud a lot better and I’ve been able to make some headway in that department.
Pix4D is pretty awesome, but it is pricey (the full 3D modeling package is, anyway). It does allow for ground control use during processing, and works really well. If we weren’t already tied to another set of software at the office, I would probably have gone with that.
I’ll check out dronedeploy, I haven’t used it. Thanks! I’m constantly experimenting, both for work and personal enjoyment, and any time I can work in some additional software knowledge, I’m happy!