Space Telescope Science Institute
DrizzlePac 2012 Handbook
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The DrizzlePac Handbook > Appendix D: Previous Drizzle Software Packages > D.6 Coordinate Transformation Tasks

D.6 Coordinate Transformation Tasks
Several supplemental tasks have also been developed using the core Drizzle Fortran code base, primarily to provide the ability to apply the Drizzle transformations to coordinates rather than to whole images. This capability allows the user to measure an object of interest in one frame and find its exact position in the other frame, making it possible to eliminate the effects of re-sampling the PSF. The tasks traxy and tranback require the user to provide the full set of transformation parameters as they would be given to drizzle or blot respectively. These tasks also have WCS-enabled versions; namely, wtraxy and wtranback. These WCS enabled versions accept the same inputs as wdrizzle or wblot to set up the parameters for the transformation, and will use the WCS from an existing image to compute the results. The task tran, on the other hand, asks for the original input image as well as the output drizzled image as created by any of the drizzle tasks and a direction for the transformation. It then reads the drizzle parameters written to the header of the output image to set up the transformation, and will automatically call either tran or tranback depending on the direction of the transformation requested by the user. All of these tasks support operations on either a single X,Y position or on a list of X,Y positions provided as an ASCII file with a column of X positions and a column of Y positions.
The second generation Drizzle tasks focused on automating the use of the original separate IRAF tasks for creating a final drizzle-combined product that was free of cosmic rays. Most of the task development was done in Python. These tasks used PyRAF to provide an IRAF epar interface to simulate the run environment of native IRAF tasks. These tasks can only be run under PyRAF or directly under Python. They included:
These Python tasks use the same core Fortran77 codebase used by the original native IRAF tasks for applying the Drizzle algorithm to the images.

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