Super Simple KAP and PhotoScan Example

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This post illustrates the use of a simple KAP rig in conjunction with structure from motion photogrammetry to generate a dense surface model of a threatened archaeological site.
Together kite aerial photography and structure from motion photogrammetry form a powerful toolkit for dense surface mapping. This post illustrates the simple camera equipment, easy to fly kite, the resulting dense surface, and a large orthographic panorama.


To take the photographs, I used a Canon S90 camera running CHDK and the Ultraintervalometer script. The camera was taped directly to the picavet. I was sure to leave a small opening so that the "S" button could be triggered. I should note that, a light weight camera permits KAP in lower wind conditions. I also occasionally fly a Canon G11, but in this case the winds would have been insufficient to lift the camera. The S90 is a really nice choice for low wind KAP mapping.
S90 Simple KAP Rig and Fled kite

In the figure below, the left hand side shows an image captured by the camera and on the right the camera in flight. Both photographs were captured simultaneously. The images were captured at the end of the photographic session as the kite lofted camera was being retrieved. All of the equipment easily fits into a backpack.
S90 Simple KAP Rig in action

The animated GIF below illustrates the 3D model that was generated from the half hour photo session. This archaeological site was previously undocumented, but I located it in Google Earth. The image displayed in Google Earth was from 2004 and the sunken circular court was in tact and undamaged. When I visited the site in 2010, the site had been severely damaged by a bulldozer. Some parties, who will remain unnamed for the time being, decided to build a road through the site. Fearing that the site might be further impacted, I stopped for a quick KAP session to record the architecture. Also visible in the image are a series of terraces. The imagery was collected in about an hour (half an hour flight time), and model was created in PhotoScan in about 4 hours. In previous posts, I've displayed 3D models as PDF files. However, some people report that the models do not display properly in their browser and PDF does not permit one to toggle model textures on and off. Thus, it can be difficult for some people to experience the model and it is difficult to evaluate the quality of the texture. Here I am experimenting with animated GIF as a "delivery" method to communicate the model.
cuchirrumi1_sm.gif

From the 3D model displayed above, it was possible to generate a orthorectified planar panorama. I output the model as a series of 10,000 x 10,000 pixel JPEG files. These files were then opened in Photoshop and assembled into a single large mosaic. I flattened the mosaic, adjusted the histograms, and saved the file in the Photoshop RAW format (note this is not the same as a camera RAW format). I uploaded the RAW file mosaic to the GigaPan website. That panorama is embedded below.. Note that the best way to view this is full screen--click here to go.

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I just started building fled kites, but my fellow Grassroots Mapper Nathan Craig is already doing 3D topographic scans with them. He's using AgiSoft's PhotoScan, which is unfortunately not open source, and costs $179.  But as he points out,... Read More

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