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B Crane

UAV and camera that support CHI Photogrammetry workflow?

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Hi,

 

I've been using the photogrammetry workflow CHI teaches to record archaeological sites/features. I've found mounting a camera on a painter's pole with a camera adapter at the end to hold a camera about 10 or so feet above the site works quite well, and allows for a lot of control over the pictures. But I quickly end up with hundreds of photographs for even a modest sized site. So, I'm looking at using a drone to allow for doing larger areas. I've been looking at the DJI Inspire 2 drone with Zenmuse X5S camera. It's a 20mp 1" sensor micro 4/3 camera that allows for interchangeable lenses, shoots in dng RAW, and seems to allow for manual focus and aperture priority shooting. Has anyone used it? Or are there any good drone/camera combinations anyone would recommend?

 

Brian

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Hi Brian, 

 

I can't speak to the specifics of the CHI workflow, but I can say more generally that there are now relatively inexpensive options in the UAV market that can achieve quite nice results. In particular, the DJI Phantom 4 Professional has a 20mp camera with a 24mm (35mm equivalent) lens that has relatively little complex distortion and produces quite high quality images, at least for a small sensor. This fixed lens can achieve good base-to-distance ratios if proper planning is observed -- it sounds as if you've already learned this with CHI -- and pretty good image accuracy, in my experience. The Professional version of the Phantom can shoot in RAW and has a mechanical shutter so you won't get the rolling-shutter effects commonly seen with GoPros and other lower-quality miniature cameras. 

 

The key is to find good flight-planning software. MapPilot will work pretty well (https://www.dronesmadeeasy.com/), as well an Australia-designed desktop software that connects to the popular Lichti app (http://www.djiflightplanner.com/). There is also the excellent UGCS flight-planning package (https://www.ugcs.com/en/page/photogrammetry-tool-for-land-surveying) but this requires you to use an Android tablet with the UAV. In my experience iOS is generally more reliable with DJI systems. 

 

As I understand it, the CHI workflow strongly encourages the use of cross-strips to increase the overall robustness of the block triangulation. I think UCGS can do this, but with the other apps you'll need to plan a second flight with cross-strips. Fortunately this isn't terribly hard. 

 

One more point I would make is that ground control is really essential for a high-quality project in archaeology, if what you want to do is map features in a site co-ordinate system. The onboard GPS of the UAV will not provide a good solution. 

 

Hope that helps. 

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Hi George,

 

Thanks for the tips, I'll check out the software you mention.The workflow I learned from CHI emphasizes using manual focus so as to keep the focus distance constant within calibration sets. Reading the manual for the Zenmuse X5S, it seems to support manual focus, but I wasn't sure about whether this was true for the camera on the Phantom 4. Certainly the Phantom 4 would be a lot more economical than the Inspire 2 with X5S camera. Both are available for rental, it seems, so maybe that's what I should do first.

 

Brian

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The Phantom does permit manual focus (it can be locked out at infiniti). It's questionable how stable that setting is between flights in terms of calibration (I am doing experiments with it), but it definitely is possible. 

 

I hope that helps!

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I've been using a Yuneec Typhoon H hexacopter (12 MP fixed focus camera) for recording archaeological sites, and have gotten excellent results. I expect that the Inspire 2 would do at least as well, if not better. For high accuracy, you will need to have ground control points measured with high accuracy (Total station, RTKGPS, or equivalent).

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I'd second the need for ground control points particularly if you are tying the photogrametric map into other maps (such as site plans or local topographic maps) with any form of precision.

Cheers Iain

 

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