Making Digital Elevations Models (DEM) on the cheap
It is a little off topic but I thought many of the forum goers might find the Photosynth to 3D process I've been working on useful for creating 3D models from aerial photos. The process is pretty simple and FREE:
· Gather images with a lot of overlap (like most of our aerial shots)
· Upload the files to http://www.photosynth.net (or use the open source Bundler app http://phototour.cs.washington.edu/bundler/ )
· Use this exporter to extract the point cloud http://pspcexporter.codeplex.com/
· Use a product like Meshlab http://www.meshlab.net/ (hard to get good results) or VrMesh Studio ( http://www.vrmesh.com/products/overview.asp ) to generate a mesh surface from the point cloud.
Here are two examples from my work in Ecuador and West Texas:
http://www.youtube.com/user/mdwillis01#p/a/u/0/2-oK5lnNA-I
and
http://www.youtube.com/user/mdwillis01#p/u/6/nJgvLll57f0 (only part of this one was done with Photoysnth).
The images were captured from kite and balloon platforms but the same workflow should work for any series of photographs.
Also, here is a Google Earth file with some of the same data http://70.114.146.89/~mwillis/Puchara_Grande.kmz (~10 Mb). My linux box connection is slow. It'll take a bit to download.
-Mark
Replies to This Discussion
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Permalink Reply by roger on -
Mark,
The 410 nadir photographs covered an area of __________ hectare/acre? Also what was the altitude, the megapixel spec of camera used, and camera model/make? Thanks.
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Permalink Reply by Mark Willis on -
Roger, The 410 photos covered an area of about 20 acres with the camera flying at about 40 meters above the ground. The landscape was rugged, covered in cactus, thorny brush, and rattle snakes. Much larger areas can be flown under better conditions or with the camera at a greater height. My main focus was to document small archaeological features. Flying t0o high would have lost a lot of detail in the imagery. It's always a give and take in this regard.
I used a Canon A590 running CHDK. You can find the specs of the camera at www.depreview.com
Hope that helps.
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Permalink Reply by roger on
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Mark,
I'm more interested on "near" ground imagery too.
Thanks for the info.
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Permalink Reply by Brian Wolfe on -
Hey Mark,
Great post, can't wait to grab some images and try it.
I'm at work and havn't had a chance to poke thru all your links, so forgive me if these questions are answered else where, but I was wondering if you could offer a few hints on acceptible overlap when grabbing images and what kind of resolution/accuracy your getting. Also, I have the ability to log the roll and pitch attitude of the plane when the images are taken. Is that info needed to get the best results? Is there a way to feed that info to the application or should I pre correct the images using Hugin or some other tool.
Thanks for sharing!
Brian
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Permalink Reply by Mark Willis on
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Brian, I haven't played around with the amount of overlap needed too much. It seems the more photographs of a location you throw at it, the higher the point cloud density. Also, it's worth noting that the detection algorithm works best on subjects with a lot of texture (like most aerial photos) but is horrible with those that don't (like glass or a shiny car). I used this PDF as a guide for my ground based work.
No telemetry data about the location of the camera is needed. I don't preprocess the images in anyway but some are trying it with varied results.
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Permalink Reply by Simon Kerr on -
Is there a package version of Bundler anywhere? I tried following the instructions that came with the binary, but failed. It appears to run, but the output file is 0 bytes.
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Permalink Reply by Mark Willis on
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Permalink Reply by Simon Kerr on
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I'm using Ubuntu, but am about to install Windows 7 via Virtualbox and reluctantly go down the Photosynth path.
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Permalink Reply by brakar on -
Mark,
I did upload a bunch of picktures to Photosynth just to see how it worked: http://photosynth.net/view.aspx?cid=3f85fd1f-fe6f-4c10-ba6b-643b8f4...
I was also able to extract a poincloud and to transform the poincloud into a mesh.
Next, I would like to create elevation curves, and to drape picktures over the mesh/dtm. Can this be done in VRMesh Studio?
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ModeratorPermalink Reply by Gary Mortimer on -
That just looks too cool, I have some sugar cane runs I'm going to process but I am struggling a bit. More interested in rendering sculptures for she who must be obeyed, would be incredible to be able to print them in plastic!
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Permalink Reply by brakar on
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Beware Gary, plastic and automatic printing... wouldn't be art... you might be in danger of getting hammered! Strange thing about the pointcloud is that it appears that the shadows from trees etc. is showing. As I understand it, shadows shouldn't have been visible - since it is only the terrain/elevation which is supposed to show. (I might have been missing something here). The sun was in the south-west at the time the picktures were taken.
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