  For air showers observed simultaneously by more than two imaging atmospheric
Cherenkov telescopes, the shower geometry is overconstrained by the images and
image information should be combined taking into account the quality of the
images. Different algorithms are discussed and tested experimentally using data
obtained from observations of Mkn 501 with the HEGRA IACT system. Most of these
algorithms provide an estimate of the accuracy of the reconstruction of shower
geometry on an event-by-event basis, allowing, e.g., to select higher-quality
subsamples for precision measurements.
