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113 
The method is of great value for the determination of systematic and accidental 
errors in photogrammetry in general, as well in the camera as in the plotters. Investiga- 
tions should be performed particularly with respect to the radial distortion of aerial 
cameras since also the influence of the atmospheric refraction and earth's curvature is 
taken into account. The accuracy of the distortion curve can easily be determined. 
The accuracy of stereoscopic plotters concerning the reconstruction of the pencils of 
rays can be determined and the quality of different plotters can be compared, concerning 
his fundamental operation. Compare Diagrams 2 and 3. 
de an 
  
Diagram 2: Diagram 3: 
Distortion curve from the dz, curve Another example of an investi- 
of diagram 1, compared with a lens gation of the distortion correc- 
distortion curve (metrogon). tion in an instrument. 
The correction of the distortion of different plotters can also easily be checked and 
the residual distortion with respect to the actual aerial camera can be determined. Also 
the accuracy of this determination can easily be found. 
The systematic errors which are introduced due to different operators and under 
different instrumental conditions (base out — base in) can be determined with similar 
procedures which is of particular interest to aerial triangulation. 
For the investigations of the influence of base in and base out, special normal equa- 
tions have to be set up and solved since the points are not symmetrically located anymore. 
An example on the treatment of this specific problem has been given in a paper by one 
of the students at Ohio State University, who determined the inner orientation of a 
projector of a Kelsh-plotter in the indicated way. See [2]: 
Formulas for the determination of the distortion. 
For completeness’ sake we will here give the formulas for the determination of the 
distortion from five sets of points in a grid. The formulas show how simple the procedure 
is and how quickly the distortion can be determined. We assume rotational symmetry in 
the system. 
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