Interpolation
Keywords: mrtcal-prog-manual

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Interpolation

The antenna offsets are derived from the Antenna Slow table together with other position values. Namely the 5 following elements have to be computed:

- lambda offset from reference position,
- beta offset,
- azimuth,
- elevation,
- local sidereal time.

All these elements are available in the `ANTSLOW` table, at a typical sampling rate of 1 Hz. Since the spectra dumps can be produced at different time sampling (no assumption is made on the rate or its variations), each spectrum positions are interpolated from the `ANT` table thanks to their respective Modified Julian Day values

| (3.1)

where is the spectrum MJD value, and is the MJD value of the trace in the `ANTSLOW` table. is computed thanks to a dichotomic search in the table such as

| (3.2)

being the interpolation fraction between the and trace, the positions are interpolated by

| (3.3)

where and are the spectrum and antenna lambda offsets respectively. Same formula applies for the beta, azimuth, and elevation values.

If is found beyond the `ANTSLOW` table limits, the boundary values are applied without extrapolation. However, this is not expected to happen since such spectra should be rejected since they are out of the on-track range.

Next: Wobbler switching Up: Antenna offsets Previous: Projection system Contents