Reference File
The resample step uses the DRIZPARS reference file.
DRIZPARS Reference File
- REFTYPE:
DRIZPARS
- Data model:
The DRIZPARS reference file contains various drizzle parameter values that control the characteristics of a drizzled image and how it is built.
Reference Selection Keywords for DRIZPARS
CRDS selects appropriate DRIZPARS references based on the following keywords. DRIZPARS is not applicable for instruments not in the table. All keywords used for file selection are required.
Instrument |
Keywords |
|---|---|
MIRI |
INSTRUME |
NIRCam |
INSTRUME |
NIRISS |
INSTRUME |
Standard Keywords
The following table lists the keywords that are required to be present in all reference files. The first column gives the FITS keyword names. The second column gives the jwst data model name for each keyword, which is useful when using data models in creating and populating a new reference file. The third column gives the equivalent meta tag in ASDF reference file headers, which is the same as the name within the data model meta tree (second column).
FITS Keyword |
Data Model Name |
ASDF meta tag |
|---|---|---|
AUTHOR |
model.meta.author |
author |
DATAMODL |
model.meta.model_type |
model_type |
DATE |
model.meta.date |
date |
DESCRIP |
model.meta.description |
description |
FILENAME |
model.meta.filename |
N/A |
INSTRUME |
model.meta.instrument.name |
instrument: {name} |
PEDIGREE |
model.meta.pedigree |
pedigree |
REFTYPE |
model.meta.reftype |
reftype |
TELESCOP |
model.meta.telescope |
telescope |
USEAFTER |
model.meta.useafter |
useafter |
NOTE: More information on standard required keywords can be found here: Standard Required Keywords
Type Specific Keywords for DRIZPARS
No additional specific keywords are required in DRIZPARS reference files, because CRDS selection is based only on the instrument name (see Reference Selection Keywords for DRIZPARS).
Reference File Format
DRIZPARS reference files are FITS format, with 1 BINTABLE extension. The FITS primary HDU does not contain a data array. The format and content of the file is as follows:
EXTNAME |
XTENSION |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|---|
DRIZPARS |
BINTABLE |
2 |
TFIELDS = 7 |
N/A |
The DRIZPARS extension contains various step parameter values to be used when processing certain types of image collections. The first two columns (numimages and filter) are used as row selectors within the table. Image collections that match those selectors then use the parameter values specified in the remainder of that table row. The table contains the following 7 columns:
TTYPE |
TFORM |
Description |
|---|---|---|
numimages |
integer |
The number of images to be combined |
filter |
integer |
The filter used to obtain the images |
pixfrac |
float |
The pixel “shrinkage” fraction |
kernel |
string |
The kernel function used to distribute flux |
fillval |
float |
Value assigned to pixels with no input flux |
wht_type |
string |
The input image weighting type |
stepsize |
integer |
Output WCS grid interpolation step size |