Assign WCS

Overview

Associates a world coordinate system (WCS) object with each science exposure.

Class: AssignWCSStep

Algorithm

In general, there may be intermediate coordinate frames depending on the instrument. The WCS is saved in the ASDF extension of the FITS file. It can be accessed as an attribute of the meta object when the fits file is opened as a data model.

Currently the Liger IRIS DRS implements a very simple model that expects standard FITS WCS keywords in the header and uses astropy.modeling to build a transformation pipeline, wrap it into a generalized WCS gwcs.WCS object and store it as output_model.meta.wcs, as it is expected by Stage 3 pipelines.

The forward direction of the transforms is from detector to world coordinates and the input positions are 0-based.

AssignWCSStep expects to find the basic WCS keywords in the PRIMARY extension header. Distortion and spectral models are not implemented yet and will be stored in reference files in the ASDF format.

Arguments

inputstr | ImagerModel | IFUCubeModel

The input data to assign a WCS for.

Subarrays

TBD.

Calibration Files

WCS reference files are in the Advanced Scientific Data Format (ASDF). The best way to create the file is to programmatically create the model and then save it to a file. A tutorial on creating reference files in ASDF format is available at:

https://github.com/spacetelescope/jwreftools/blob/master/docs/notebooks/referece_files_asdf.ipynb

Transforms are 0-based. The forward direction is from detector to sky.