A register glass type reseau is a very useful addition to 
a eamera for analytical aerial triangulation, 1f it is 
measured with an accuracy at least as good as that for the 
measurements of well-defined image points. It should also 
be realized that the overall lens distortion should be 
corrected, not only its radial component or, still worse, 
an average radial component. It has been shown that the 
error resulting from disregarding the so-called tangential 
Jens distortion ean be substantial.