Option 2 : Implementation based on an empirical approach

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Description:

We would need to derive two transformation matrices:

• SKY_TO_FP

• FP_TO_CCD

These matrices would need data which would be:

• Imaging of astrometric data at different drive angles

• Imaging data of the focus pinhole

Method:

1. Derive a transformation from FP_TO_CCD based on the focus images. Shui has done some of that using the routines to focus DEIMOS.

2. Observe an astrometric field with DEIMOS (close to senith) at 5-10 drive values to derive a SKY_TO_CCD transformation.

3. Use the FP_TO_CCD and the SKY_TO_CCD transformation to derive a SKY_TO_FP transformation per drive angle.

4. Determine what the best transformation to use. One option is to combine all the SKY_TO_FP per angle into one.