DISTORTION Reference File

REFTYPE:

DISTORTION

Data model:

DistortionRefModel

The distortion reference file contains a combination of astropy models, representing the transform from detector to the telescope V2, V3 system. The following convention was adopted:

• the input x and y are 0-based coordinates in the DMS system;

• the output is in the V2, V3 system;

• the center of the first pixel is (0, 0), so the first pixel goes from -0.5 to 0.5;

• the origin of the transform is taken to be (0, 0). Note that while a different origin can be used for some transforms the relevant offset should first be prepended to the distortion transform to account for the change in origin of the coordinate frame.

Internally the WCS pipeline works with 0-based coordinates.

Reference Selection Keyword Attributes for DISTORTION

CRDS automatically selects the appropriate DISTORTION reference files based on the following keyword attributes.

N.B.: DISTORTION is not applicable for instruments not in the table.

Instrument	Keyword Attributes
WFI	instrument, detector, optical_element, date, time

Standard ASDF metadata

The following table lists the attributes that are required to be present in all reference files. The first column shows the attribute in the ASDF reference file headers, which is the same as the name within the data model meta tree (second column). The second column gives the roman data model name for each attribute, which is useful when using data models in creating and populating a new reference file.

Attribute	Fully Qualified Path
author	model.meta.author
model_type	model.meta.model_type
date	model.meta.date
description	model.meta.description
instrument	model.meta.instrument.name
reftype	model.meta.reftype
telescope	model.meta.telescope
useafter	model.meta.useafter

NOTE: More information on standard required attributes can be found here: Standard ASDF metadata

Reference File Format

DISTORTION reference files are ASDF format, and contain an astropy model object. The format and content of the file is as follows (see DistortionRefModel):

Data	Data type
coordinate_distortion_transform	astropy.modeling.Model

The ASDF file contains a single astropy model object.

model:

Transform from detector to an intermediate frame (instrument dependent).