This routine will resample each input 2D image based on the WCS and distortion information, and will combine multiple resampled images into a single undistorted product. The distortion information should have been incorporated into the image using the latest assign_wcs pipeline step.

The resample step can take as input either
  • a single 2D input image updated by assign_wcs
  • an association table (in json format)

The pipeline defined parameters for the drizzle operation itself get provided by the DRIZPARS reference file (from CRDS). The exact values used depends on the number of input images being combined and the filter being used. Other information may be added as selection criteria later, but for now, only basic information is used.

The output product gets defined using the WCS information of all inputs, even if it is just a single input image. This output WCS defines a field-of-view that encompasses the undistorted footprints on the sky of all the input images with the same orientation and plate scale as the first listed input image.

It uses the interface to the C-based cdriz routine to do the resampling via the drizzle method. The input-to-output pixel mapping is determined via a mapping function derived from the WCS of each input image and the WCS of the define output product. This mapping function gets passed to cdriz to drive the actual drizzling to create the output product.

A full description of the drizzling algorithm, and parameters for drizzling, can be found in the DrizzlePac Handbook.