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Geoinformatics_05-2009
article using pixoview technology testing measurement accuracy in oblique photography with an increase in applications relating to the use of oblique photography, there is now a demand to determine what degree of accuracy can be achieved with oblique photography single-picture measurements in the pixoview application. by jan sukup, patrik meixner and karel sukup fig. 1: flight plan and ground control point coverage of the test project area. fig. 2: calibration protocol detail example. testing project since 2006, pixoview technology has been under development at geodis brno, for processing oblique photographs. pixoview makes available the possibility of processing generally-oriented aerial and terrestrial photographs in a single database, which allows for simple control of a suitable selection of photographs for further processing. currently, work is mainly focused on monoscopic measuring of individual image content displayed on computer monitors. the oblique photography technology can be divided into two stages. the first stage involves exposing oblique photographs, for which geodis brno, ltd., uses a z-37a čmelak aircraft fitted with a system consisting of five cameras secured in a fixed group called gbcam i. one camera captures vertical photographs, while the others are tilted to the left and right, forward and backward to acquire the oblique images. the second technology stage involves the subsequent processing of digitally-acquired photographs using single-image aerial photogrammetry. the purpose of the spring 2008 testing project was mainly to determine positional and vertical measuring accuracy of the pixoview application. the testing itself was performed on aerial photographs taken around brnoliseň, where geodis brno has a calibration base with 80 signalized control points defined by gps technology. for testing purposes a three-camera system was used. cameras labeled c1, c2, and c3 each took 71 photographs in 9 flight strips over the 180 hectare area of interest. since the flying height was ca 650 m above terrain, photographs had a nadir resolution of 0.1 m, and the oblique photograph resolution decreased proportionally to a value of ca 0.2 m, based on subject distance from the projection centre. input data the input data for each project in pixoview includes: aerial (terrestrial) images io interior orientation parameters eo exterior orientation parameters dtm digital terrain model the pixoview application obtains interior orientation parameters via a calibration protocol (fig.2), which provides information on the camera focal length (f ), the position of the principal point (dx, dy), and the radial lens distortion values. these variables define the position of the projection centre with respect to the level of the exposure, allowing us to later reconstruct the visual cluster of rays that created the aerial photograph at the time of its exposure. to place this cluster in space, with regard to the geodetic coordinate system, it is necessary to know the exterior orientation parameters which define the position of the projection centre in the appropriate coordinate system as given by three coordinates (x, y, z). in addition, the frame axis orientation in space is represented by three angles of rotation (ω, ϕ, κ). the eo parameters can be determined in three ways: by direct georeferencing by analytical aerotriangulation without ground control points by analytical aerotriangulation using ground control points the direct georeferencing of aerial photographs means obtaining the eo parameters directly by processing the data gathered by the gps july/august 2009 36
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