A software assistant for manual stereo photometrology

[摘要] A software package was written under the X Window System, Version 11, to assistin manual stereopsis of multiple views. The package enables multiple high resolution(2000 by 1500 pixels and higher) black and white photographs to be viewed simultaneously.Images have adjustable zoom windows which can be manipulated with thepointing device. The zoom windows enlarge to many times the resolution of the imageenabling sub-pixel measurements to be extrapolated by the operator. A user-friendlyinterface allows for fast pinhole camera calibration (from known 3D calibration points)and enables three dimensional lines, circles, grids, cylinders and planes to be fittedto markers specified by the user. These geometric objects are automatically renderedin 3D for comparison with the images. The camera calibration is performed usingan iterative optimisation algorithm which also tries multiple combinations of omittedcalibration points. This allows for some fault tolerance of the algorithm with respectto erroneous calibration points. Vector mathematics for the geometrical fits is derived.The calibration is shown to converge on a variety of photographs from actualplant surveys. In an artificial test on an array of constructed 3D coordinate markers,absolute accuracy was found to be 1 mm (standard deviation of the Euclidean error)for a distance of 2.5 meters from a standard 35 mm camera. This translates to anerror of 1.6 pixels in the scanned views. Lens distortion was assumed to be negligible,except for aspect ratio distortion which was calibrated for. Finally. to demonstratethe efficacy of the package, a 3D model was reconstructed from ten photographs of ahuman face, taken from different angles.

[发布机构] University of the Witwatersrand