3. Astrometry

Commnd: wisp-solve-astrometry

Important Parameters

• astrometry-catalog-max-magnitude

• max-srcmatch-distance

• astrometry-order

• min-match-fraction

• max-rms-distance

• frame-center-estimate

• frame-fov-estimate

• anet-api-key if using the online astrometry.net service.

Description

The wisp-solve-astrometry command finds the transformation that converts sky coordinates (right ascention and declination) into image coorditanes (x, y). This allows the use of external catalogue data for more precise positions of the sources than can be extracted from survey images and also the use of auxiliary data provided in the catalogue about each source, in the subsequent processing steps of the pipeline.

Astrometry is accomplished in 2 steps. First, AutoWISP uses astrometry.net to find an initial match between the few tens (to few hundred) brightest extracted source to the Gaia catalog, and then iteratively refines this match and the transformation parameters to match almost every single extracted source to its catalog counterpart. For wide-field images, this means thousands of matches that are used to find the transfomation parameters, allowing AutoWISP to model transformation involving signifiacant image distortion, which often occurs in wide-field images.