3D aerial scan of Bronze Age long barrow

As part of an archaeological project aimed at developing a 'standard' approach to low-altitude UAV surveying I spent a lovely and very productive couple of hours at Stoney Littleton Long Barrow near Bath. The site is amazing and is one of the finest accessible examples of a Neolithic chambered tombs in the UK, with multiple burial chambers which are open to view.

The actual survey was done with a DIY hexacopter, based around an APM 2.6. I used a Canon point-and-shoot running CHDK and an intervalometer script. The actual survey was done in under an hour.

A resulting 3D photogrametry model, created using Autodesk's free to use 123D Catch can be viewed here.

The main goal was not perfection but coming up with a procedure that most people can follow and which gives pretty good results. 

If you'd like to get involved we're inviting feedback on our good practice guide.

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Moderator
Comment by Gary Mortimer on June 19, 2014 at 10:20am

Nicely done


3D Robotics
Comment by Chris Anderson on June 19, 2014 at 10:24am

That's fantastic! And 123D Catch did quite a good job of stitching it, too. Thanks for sharing!

Comment by John on June 19, 2014 at 7:32pm
That is very inspiring. I'm thinking if using a spare iphone as a camera with an intermittent photo setting. I can set in 2 second increments. What was your time setting? And the camera needs to be pointing straight down?
Comment by Jack Crossfire on June 19, 2014 at 9:37pm

The CHDK intervalometer was pretty bad, years ago, limited to 5 second intervals even though the cameras could do 0.5 second intervals in continuous mode.  CHDK didn't support continuous shooting, of course. 

Comment by Aaron Curtis on June 19, 2014 at 9:59pm

Do you think the curvature of the ground is correct? If not, there is a known issue that I've encountered which you may need to consider: http://ccwu.me/file/radial.pdf


MR60
Comment by Hugues on June 19, 2014 at 11:42pm

@Aaron, very interesting article (not the maths though :). this is indeed relatively well known that you get flat surface curvature when doing a 3D reconstruction. I know an expert here in Belgium who uses the (relatively complicated because all in CLI mode) MICMAC opensource software (it is in fact a suite of image processing tools developed by the French national mapping organisation) to do his 3D reconstructions and able, if I understoos right, to correct this kind of curvature.

Comment by Stephen Gray on June 20, 2014 at 1:33am

@John thanks, the interval was 2secs, though it can be longer if you fly higher and yes the camera has to be vertical @Jack CHDK now shots as quickly as the camera is mechanically capable which is ideal @Aaron thanks, that was the very next point I was going to tackle, though as @Hugues points out, a simple way of sorting the issue is badly needed I'll go look at MICMAC

Comment by Aaron Curtis on June 20, 2014 at 7:34am

@Jack, I use VisualSFM for my 3D mapping. VisualSFM does estimate the radial distortion of each image (actually I think it's done by PMVS-- VisualSFM is just a gui) and creates undistorted images before doing the dense reconstruction. I have not noticed strong distortion in my 3D landscape models but I'm not sure if it's because of this undistortionstep, the fact that I'm using a near-rectilinear lens to begin with, or if I've just been lucky so far. VisualSFM is excellent, though and I highly recommend it.

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