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This section describes work in progress concerning ACIS ray
tracing. The problem we want to solve consists of the following: given
a photon emerging from the HRMA from a given direction, we want to
determine which CCD the photon will hit and the pixel coordinates of
the event. Our input information is the direction of the incoming
photons (in terms of three direction cosines) from an arbitrary point
outside the mirror. This information will be provided by the ASC
program SAOSAC (see the XRCF Phase 1 report
). The problem consists of
finding the (unique) intersection of the ray trajectory with the CCD
surface, taking into account the tilt of the latter with respect to
the HRMA optical axis.

11/20/1997