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- May 27, 2017
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- Los Alamos, NM
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- www.mavicpilots.com
I'd think they'd implement it so that just the immediate area around the flight is downloaded/used...and that should make the file sizes quite manageable.
And as far as the cost goes, they look to be free in the U.S. from the USGS...
Where can I get elevation data?
Download free digital elevation data through The National Map Download Client. Click the “How To” link at the top of the viewer for detailed instructions on how to find and download data; see The National Map training videos for step-by-step demonstrations.Download standard elevation products...www.usgs.gov
How often would you suspect people are taking off from locations that are at a significantly different elevation than ground level? I've heard of people taking off from the roof of a building, or maybe the balcony of a hotel at the beach, but that seems quite rare to me. You could always compare the GPS data to the DEM value for the take-off location and ask the user for confirmation if there's a discrepancy.
Honestly, I'm not at all familiar with DEMs and how accurate the data is. I just guessed that there might be a way to download only a portion of the data, similar to the way an Android user can download portions of the Google map data, without the need to store hundreds of GB of information. And I would store all of the data and do all of the calculations on the users device, rather than in the aircraft or the RC.
But then again, I am only looking at this as a (far from expert) semi-pro programmer. And things always seem to get more complicated once you start writing code.
The problem with downloading DEM data as needed is that it relies on a reasonable internet connection. But that would be a possibility if the lack of height AGL in many situations were acceptable.
With 30 m DEM resolution the takeoff elevation is going to be significantly wrong in many situations - and typically worst in the kind of terrain where height AGL would be most important. And my guess is that DJI won't do this, if only because most flights are at heights where the ground elevation is only one part of the equation, i.e. the height of structures and vegetation is significant compared to the aircraft height. I foresee many people simply trusting the height AGL, flying into trees and building, and then blaming DJI.