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Computing the pixel coordinates

Given the actual position of the derotator, MRTCAL can compute the pixel position on sky from the current telescope position. This position has been pre-computed using the radio projection ( LONGOFF and LATOFF columns in the IMB-FITS), only the per-pixel offsets are to be added. MRTCAL checks first if it knows the offsets for the current receiver (as found in the column RECNAME in the frontend table). The pixels offsets are not self-described in the IMBFITS: they must be hardcoded in the program, with a correct correspondance between the pixel number found in the backend table and the hardcoded offsets3.3. Once the offset of the current pixel is found, the strategy is the following.

The deprojection, offset in spherical coordinates, and reprojection are done by the Gildas internal engines.


next up previous contents
Next: Description of the radio Up: Offsets of multi-pixel receiver Previous: Handling the derotator   Contents
Gildas manager 2023-06-01