Agisoft Lens – Lens Calibration Without Three Orientations

The class shot photos of the Kitchen, Indian Room and Pantry during our first visit to Georgia O’Keefe’s house, using the previously established method in which we shot one photo in horizontal orientation and two photos in vertical orientation utilizing 60 to 80 percent overlap.  Additionally, all corner surfaces of the rooms were fanned utilizing transitions at 15 degree increments, also utilizing the same three shot technique. Upon returning and processing the meshes, we encountered the following issues.

The amount of photos required to create a point cloud proved prohibitive, due to the size of the rooms. Available processing power, even in the most robust computer workstation the Media Arts program possesses, proved slow and yielded inconsistent results.

Attempting to find a resolution to the issue, Mariano researched methods, as outlined by the PhotoScan user’s guide.  This research produced the following results. The amount of photos required for the three photo per station method was necessary to compensate for inherent lens distortion. The vertical shots allowed PhotoScan to generate the information necessary to create accurate camera positions in the point cloud. PhotoScan allows the user to customize settings based on lens calibration. The process involves the photographing of a high contrast display at 60 to 80 percent overlap in a horizontal fashion. The resulting data can be saved and input into the program specific to the lens used to shoot the object or location. The calibration allows the photographer to shoot 2/3 fewer photos, eliminating the vertical shots of the original method. Instead, the software compensates for lens distortion based on values gathered during the calibration method. The class utilized the lens calibration method during the second visit, re-photographing the rooms from the initial visit and adding O’Keefe’s studio. Additionally, we shot various objects utilizing the same method. The shoot proved more efficient, both on time and resources. The following results were observed.

Objects photographed utilizing the lens calibration method produced consistent point clouds and accurate representations of the object photographed.

Rooms photographed utilizing this same method produced less consistent results.  Point clouds were less accurate with holes and inconsistent representations of surfaces.

Subsequent research and searches for successfully rendered interior spaces utilizing photogrammetry proved futile.  Notably, the disparity between successfully created exteriors and objects, compared to successfully created interiors was noted, leading us to reason that 3d Scanning and virtual panoramas instead of photogrammetry might prove more successful.  To this end, we constructed a Pan-O-Head to explore the results this method would produce.  Results to come.

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