# Offsets of multi-pixel receiver

In the IMBFITS files, the backend table describes how the chunks cover the bandwidth and from which receiver they come from (e.g. H or V polarization). In this table, the column PIXEL also describes from which pixel the signal comes. This is useful in the context of multi-pixel receivers. In such a case, there are several pixels which do not look at the same position on sky. In the frontend table header, the derotator mode (sky, frame, or horizontal) and angle describe the commanded inputs from the user. The derotator table, which is present in the IMBFITS files only if relevant, describes the commanded and actual derotator position through time, at typical intervals of 5 seconds. We describe below how MRTCAL makes use of these informations.

Subsections

- Handling the derotator
- Computing the pixel coordinates
- Description of the radio projection
- In practice: Effect on Polaris observations