tweakreg_step

The tweakreg_step function (class name TweakRegStep) is the top-level function used to call the “tweakreg” operation from the Roman Calibration pipeline.

Roman pipeline step for image alignment.

class romancal.tweakreg.tweakreg_step.TweakRegStep(name=None, parent=None, config_file=None, _validate_kwds=True, **kws)

TweakRegStep: Image alignment based on catalogs of sources detected in input images.

Create a Step instance.

Parameters:

• name (str, optional) – The name of the Step instance. Used in logging messages and in cache filenames. If not provided, one will be generated based on the class name.

• parent (Step instance, optional) – The parent step of this step. Used to determine a fully-qualified name for this step, and to determine the mode in which to run this step.

• config_file (str or pathlib.Path, optional) – The path to the config file that this step was initialized with. Use to determine relative path names of other config files.

• **kws (dict) – Additional parameters to set. These will be set as member variables on the new Step instance.

class_alias = 'tweakreg'

do_absolute_alignment(ref_image, imcats)

Perform absolute alignment of images.

This method retrieves a reference image and performs absolute alignment using the specified parameters, including reference WCS information and catalog details. It aligns the provided image catalogs to the absolute reference catalog.

Parameters:

• ref_image (DataModel) – The reference image used for alignment, which contains WCS information.

• imcats (list) – A list of image catalogs containing source information for alignment.

Return type:

None

do_relative_alignment(imcats)

Perform relative alignment of images.

This method performs relative alignment with the specified parameters, including search radius, separation, and fitting geometry.

Parameters:

imcats (list) – A list of image catalogs containing source information for alignment.

Return type:

None

get_tweakreg_catalog(source_catalog, image_model)

Retrieve the tweakreg catalog from source detection.

This method checks the source detection metadata for the presence of a tweakreg catalog data or a string with its name. It returns the catalog as a Table object if either is found, or raises an error if neither is available.

Parameters:

• source_catalog (object) – The source catalog metadata containing catalog information.

• image_model (DataModel) – The image model associated with the source detection.

Returns:

The retrieved tweakreg catalog as a Table object.

Return type:

Table

Raises:

AttributeError – If the required catalog information is missing from the source detection.

process(input)

This is where real work happens. Every Step subclass has to override this method. The default behaviour is to raise a NotImplementedError exception.

read_catalog(catalog_name)

Reads a source catalog from a specified file.

This function determines the format of the catalog based on the file extension:

• “asdf”: uses roman datamodels

• “parquet”: uses pyarrow

• otherwise: uses astropy Table.

Parameters:

catalog_name (str) – The name of the catalog file to read.

Returns:

The read catalog as a Table object.

Return type:

Table

Raises:

ValueError – If the catalog format is unsupported.

reference_file_types: ClassVar = []

spec = "\n        use_custom_catalogs = boolean(default=False) # Use custom user-provided catalogs?\n        catalog_format = string(default='ascii.ecsv') # Catalog output file format\n        catfile = string(default='') # Name of the file with a list of custom user-provided catalogs\n        catalog_path = string(default='') # Catalog output file path\n        enforce_user_order = boolean(default=False) # Align images in user specified order?\n        expand_refcat = boolean(default=False) # Expand reference catalog with new sources?\n        minobj = integer(default=15) # Minimum number of objects acceptable for matching\n        searchrad = float(default=2.0) # The search radius in arcsec for a match\n        use2dhist = boolean(default=True) # Use 2d histogram to find initial offset?\n        separation = float(default=1.0) # Minimum object separation in arcsec\n        tolerance = float(default=0.7) # Matching tolerance for xyxymatch in arcsec\n        fitgeometry = option('shift', 'rshift', 'rscale', 'general', default='rshift') # Fitting geometry\n        nclip = integer(min=0, default=3) # Number of clipping iterations in fit\n        sigma = float(min=0.0, default=3.0) # Clipping limit in sigma units\n        abs_refcat = string(default='GAIADR3')  # Absolute reference\n        # catalog. Options: GAIADR3,GAIADR2,GAIADR1\n        save_abs_catalog = boolean(default=False)  # Write out used absolute astrometric reference catalog as a separate product\n        abs_minobj = integer(default=15) # Minimum number of objects acceptable for matching when performing absolute astrometry\n        abs_searchrad = float(default=6.0) # The search radius in arcsec for a match when performing absolute astrometry\n        # We encourage setting this parameter to True. Otherwise, xoffset and yoffset will be set to zero.\n        abs_use2dhist = boolean(default=True) # Use 2D histogram to find initial offset when performing absolute astrometry?\n        abs_separation = float(default=1.0) # Minimum object separation in arcsec when performing absolute astrometry\n        abs_tolerance = float(default=0.7) # Matching tolerance for xyxymatch in arcsec when performing absolute astrometry\n        # Fitting geometry when performing absolute astrometry\n        abs_fitgeometry = option('shift', 'rshift', 'rscale', 'general', default='rshift')\n        abs_nclip = integer(min=0, default=3) # Number of clipping iterations in fit when performing absolute astrometry\n        abs_sigma = float(min=0.0, default=3.0) # Clipping limit in sigma units when performing absolute astrometry\n        output_use_model = boolean(default=True)  # When saving use `DataModel.meta.filename`\n        update_source_catalog_coordinates = boolean(default=False) # Update source catalog file with tweaked coordinates?\n        save_l1_wcs = boolean(default=True)\n    "

update_catalog_coordinates(tweakreg_catalog_name, tweaked_wcs)

Update the source catalog coordinates using the tweaked WCS.

Parameters:

• tweakreg_catalog_name (str) – The name of the TweakReg catalog file produced by SourceCatalog.

• tweaked_wcs (gwcs.wcs.WCS) – The tweaked World Coordinate System (WCS) object.

Return type:

None