For more details about step arguments (including datatypes, possible values and defaults) see romancal.resample.ResampleStep.spec.

Step Arguments

The resample step has the following optional arguments that control the behavior of the processing and the characteristics of the resampled image.

--pixfrac

The fraction by which input pixels are “shrunk” before being drizzled onto the output image grid, given as a real number between 0 and 1.

--kernel

The form of the kernel function used to distribute flux onto the output image. Available kernels are square, gaussian, point, tophat, turbo, lanczos2, and lanczos3.

--pixel_scale_ratio

Ratio of input to output pixel scale. A value of 0.5 means the output image would have 4 pixels sampling each input pixel. Ignored when pixel_scale or output_wcs are provided.

--pixel_scale

Absolute pixel scale in degrees. When provided, overrides pixel_scale_ratio. Ignored when output_wcs is provided.

--rotation

Position angle (in degrees) of output image’s Y-axis relative to North. A value of 0.0 would orient the final output image to be North up. The value of None specifies that the images will not be rotated, but will instead be resampled in the default orientation for the camera with the x and y axes of the resampled image corresponding approximately to the detector axes. Ignored when pixel_scale or output_wcs are provided.

--crpix

Position of the reference pixel in the image array in the x, y order. If crpix is not specified, it will be set to the center of the bounding box of the returned WCS object. When supplied from command line, it should be a comma-separated list of floats. Ignored when output_wcs is provided.

--crval

Right ascension and declination of the reference pixel. Automatically computed if not provided. When supplied from command line, it should be a comma-separated list of floats. Ignored when output_wcs is provided.

--output_shape

Shape of the image (data array) using “standard” nx first and ny second (as opposite to the numpy.ndarray convention - ny first and nx second). This value will be assigned to pixel_shape and array_shape properties of the returned WCS object. When supplied from command line, it should be a comma-separated list of integers nx, ny.

Note

Specifying output_shape is required when the WCS in output_wcs does not have bounding_box property set.

--output_wcs

File name of a ASDF file with a GWCS stored under the "wcs" key under the root of the file. The output image size is determined from the bounding box of the WCS (if any). Argument output_shape overrides computed image size and it is required when output WCS does not have bounding_box property set.

Note

When output_wcs is specified, WCS-related arguments such as pixel_scale_ratio, pixel_scale, rotation, crpix, and crval will be ignored.

--resample_on_skycell

If input association contains skycell information use it to compute the output wcs. If output_wcs is defined it will be used instead. If resample_on_skycell is False the output wcs will be the combined wcs of all input models.

--fillval

The value to assign to output pixels that have zero weight or do not receive any flux from any input pixels during drizzling.

--weight_type

The weighting type for each input image. If weight_type=ivm, the scaling value will be determined per-pixel using the inverse of the read noise (VAR_RNOISE) array stored in each input image. If the VAR_RNOISE array does not exist, the variance is set to 1 for all pixels (equal weighting). If weight_type=ivm-sky, the scaling value will be determined per-pixel using the inverse of the sky variance (VAR_SKY) array stored in each input image. If weight_type=exptime, the scaling value will be set equal to the exposure time found in the image header.

Note

VAR_SKY is calculated as follows:

VAR_SKY = VAR_RNOISE + VAR_POISSON / DATA * MEDIAN(DATA)

where VAR_RNOISE is the read noise variance, VAR_POISSON is the Poisson noise variance, DATA is the science data, and MEDIAN(DATA) is the median of the science data.

--in_memory

If set to False, write output datamodel to disk.

--good_bits

Specifies the bits to use when creating the resampling mask. Either a single bit value or a combination of them can be provided. If the string starts with a tilde (), then the provided bit(s) will be excluded when creating the resampling mask. A value of ~DO_NOT_USE+NON_SCIENCE will exclude pixels flagged with DO_NOT_USE and NON_SCIENCE.

The bit value can be provided in a few different ways, but always as a string type. For example, if the user deems OK to use pixels with low QE and highly nonlinear, then any of the ways listed below will work to set good_bits:

  • good_bits = 'LOW_QE+NON_LINEAR' (concatenated DQ flag labels);

  • good_bits = '8192+65536' (concatenated DQ flag bit values);

  • good_bits = '8192,65536' (comma-separated DQ flag bit values);

  • good_bits = '73728' (sum of DQ flag bit values).

Note

Adding a tilde () to the beginning of the string will flip the bit(s) and actually exclude the provided bit(s). This is the same as providing the bad bits instead of the good bits.