Stratigraphic Photogrammetry: Part 2 – A Quick Proof of Concept


I’ve been moving along, making progress on my methodology for stratigraphic photogrammetry. I don’t remember just off of the top of my head, but I think that the actual title of the paper is something like A Method for the Use of a Non-Metric Digital Camera in Stratigraphic Photogrammetry. I present the paper (which I will post here as soon as I am able, although I think that I want to have it edited by someone else before I post it here) on Wednesday morning. As part of finishing the paper, to show that my method can overcome the basic obsticles in using a non-metric camera to make metric photographs, I set up a flight-line on one of the public trails in the area and took a series of stereo photographs (digital images, actually) of a stratigraphic profile, as a proof-of-concept.

I set up on the John Wayne Trail in Eastern Ellensburg, Washington. The John Wayne Trail is a public jogging trail created along an old railroad prism and cuts. After weeks of plotting and figuring and calculation, I really didn’t know what to expect when I went out to take my images. craig2s.jpgI was pretty confident in my calculations for scale and coverage, but I really didn’t know. It turns out that my biggest problem wasn’t the photogrammetric method at all. The biggest problem was that most of the tasks of setting up a flight-line require two or three people to do them. I should have known that it would take more people. All of the things I needed to do, like pulling level lines and measuring grids, etc. are things that I have done before on monitoring projects or at the mammoth dig this summer. I really should have guessed that I wouldn’t have much luck trying to dig my toes into a slick clay slope, pull a metric tape and a level line with one hand, place a grid-corner nail with the other before hurrying to grab my hammer and try to pound the nail in before it fell. I eventually gave up trying to build a reference grid onto the wall, which would have been a necessary step if I was planning on orthorectifying my images to overcome radial distortion caused by the short focal length and cheap lense of my camera. craig3s.jpgLuckily, I was trying to create stereo images, which no longer show stereo if they are orthorectified, and so had no real need for the reference grid. Overall the images turned out even better than I expected. I couldn’t get right at the wall, so I had to pull back away from it to 10m. This put the visible stratigraphy at the very top of the image: much smaller that I had hoped for, but more than enough under the circumstances. The images do indeed show up in 3D under a stereoscope.

If you click on the thumbnails you can see bigger versions of the images, but even those are small, poor quality versions. I reduced the resolution to save bandwidth. If you have any interest in the full-resolution pictures, just drop me a note, either by e-mail, or in the comments to this post, and I will send them to you.

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