Rabu, 11 Maret 2009

Photogrammetry Meets Kite Aerial Photography (KAP)

Kite Aerial Photography, as the name suggests, involves rigging a camera up to a kite system and then using it to take aerial photographs. After seeing my previous post on photogrammetry with a camera attached to a helium-balloon, Dr. Mike Smith at Kingston University contacted me about research he has been conducting in the realm of KAP and photogrammetry. Along with Drs. Chandler and Rose, he recently published a paper in Earth Surface Processes and Landforms entitled "High spatial resolution data acquisition for the geosciences: kite aerial photography".

The paper is relevant for the mapping industry because it provides an overview of the aerial acquisition process, the photogrammetric processing, and then an accuracy assessment of the results. I'll start with the results: their methodology enabled the production of stereo pairs, digital elevation models, and stereo imagery. Furthermore, the stereo imagery was triangulated with an accuracy of roughly 10mm in planform against surveyed ground control points.

The methodology involved using a 6 megapixel Nikon D70 camera and collecting aerial photography at altitudes of up to 200 meters over three test sites in the UK. GCP targets and XYZ samplings for topographic modeling were measured with Leica Geosystems TPS1200 and TCA 1105 Total Stations.

All the photogrammetric processing was performed in LPS. This involved setting up an LPS Blockfile (a project file), adding the images, and subsequently running through the aerial triangulation process in LPS Core in order to produce stereo pairs. With oriented images, the LPS Automatic Terrain Extraction module could be used to generate a digital elevation model. Next, the oriented images along with the digital terrain could be used to produce digital orthophotos. The paper describes the process in a high level of detail, as well as an excellent evaluation and discussion of the results.

Here is an image of an orthophoto superimposed with terrain points (red = automatically extracted, blue = measured via total station):

And here is a perspective view of an orthophoto draped over a corresponding digital elevation model, with contours:
In my opinion it is a great looking product considering it was generated with a 6 megapixel SLR camera flown from a kite!!

So why is this relevant for the mapping business?

The study illustrates a great low-cost approach to localized (as opposed to wide area) mapping, which means it may very well be a viable option for applications ranging from mapping cultural heritage sites to localized studies on soil erosion and other environmental and natural resource mapping projects. It is significant because it represents a significant cost saving over the traditional helicopter-based approach. If I had any talent for flying big kites I'd give it a whirl, but for now I'll leave it to he pro's...

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