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Author Topic: DEM Elevation Drift using Phantom 4  (Read 3155 times)

dsMapper

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DEM Elevation Drift using Phantom 4
« on: April 06, 2018, 03:05:16 AM »
Hello,
I am a relatively new user to Agisoft and photogrammetery in general.  My  primary interest is producing Orthophotos and DEMs. 

I have flown about 6 flights now and noticed a similar issue with all of them; the elevation shown on the DEM of the ground surface appears to drift up over the course of the flight.  The most obvious map I've observed this was a low flight conducted at 20 meters above the ground surface. The area I was mapping is about 1 hectare (2.5 acres) and other then some boulders is completely flat; at most 1 meter of elevation change across the area.  The resulting DEM shows 8 meters of elevation change. Any idea how to correct the issue?

Things I've tried already:
* I've tried uploading the same photo set to drone deploy and did not see the same error. 
* I tried adding fake ground control points using google earth elevations; but I get a "bowl" affect between the GCPs
* I tried editing the exif data to use the relative barometer elevation plus an offset; still same relative result.
* I tried calibrating my camera using the Agisoft chessboard and did not see a noticeable difference. 


Thank you in advance for your time!


GPC

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Re: DEM Elevation Drift using Phantom 4
« Reply #1 on: April 07, 2018, 04:11:21 AM »
Get more accurate positioning in the uav or add real ground control. There's no other solution.
When things get weird, the weird turn pro.

SAV

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Re: DEM Elevation Drift using Phantom 4
« Reply #2 on: April 07, 2018, 11:17:10 PM »
Hi dsMapper,

If you want to get accurate spatial datasets, you will either need to use accurately surveyed ground control points (cm accuracy) or a UAV that records camera locations at cm accuracy (PPK or RTK capabilities), as already mentioned by GPC.

You also have to make sure that your image quality is good (blurry images are bad) and acquire imagery with a  high overlap (depends on the scene complexity, but I would always choose a value higher than 70%).

You might also find one of my older posts useful:
http://www.agisoft.com/forum/index.php?topic=7851.msg37494#msg37494

All the best.

Regards,
SAV
« Last Edit: April 07, 2018, 11:19:39 PM by SAV »