Aerotri, Aerial Triangulation Adjustment and Camera Calibration

Aerotri carries out a bundle block adjustment, the most accurate and powerful method, since it uses all the data as a whole, making the most of it. The power of bundle block adjustment is further improved by robust estimation tecniques, allowing automatic gross error detection, shoud the errors appear among the photo coordinates, control points or GPS/INS data.

It is highly optimized for both storage space and, specially, for time consuming, making it the optimum tool for large blocks adjustments. A 1000 photographs flight with GPS data takes less than 1 minute in a 2000MHz computer.

Aerotri reads between two and four input files: photo coordinates, control, GPS/INS and calibration data. It generates an ouput file with all the information about the adjustment process, both in text and html format, and the .ori file needed to create ortophotographs. Control points can be included in the adjustment or stay invariant. Moreover, Aerotri calculates drift GPS and INS parameters, correcting the coordinates from that error.

A grafic of the flight is generated, with an accurate representation of the photographs over the earth surface, the points and the error ellipses. This grafic can be exported to a dgn file, both 2D and 3D, even if you are working with UTM coordinates and milimetric precision, as well as to the Digin .bin format. Finally, a pdf report sheet is also generated.

Calibration

The calibration module is based upon a distortion model designed to allow for the modelling of the distortion of any central projection camera, from metric cameras, be it analogic or digital, to amateur cameras. Parameters are independent from one another, and among all possible combinations of orientation/distortion, the program always finds that one for wich the distortion is minimum.

The calibration result may be included in the program Aerotri, in order to take the distortions out from the measurements.

Models

A model transformation module is also included. It performs a three dimensional similarity transformation (with the choice of not to include a scale fator) among two coordinate systems, and it transforms all the points to the reference system, including the rotation matrices of projection centres, if they exist.

The algorithm used furnishes a fast and rigorous solution, with a calculation time increasing linearly with respect to the number of points, thus making the program an idoneous tool for the computation of transformation parameters between two systems when a large number of points is available.