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Diffstat (limited to 'doc/source')
| -rw-r--r-- | doc/source/fits_conventions.rst | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/doc/source/fits_conventions.rst b/doc/source/fits_conventions.rst index 3067497..0938857 100644 --- a/doc/source/fits_conventions.rst +++ b/doc/source/fits_conventions.rst @@ -182,12 +182,19 @@ have a unique suffix, **_npl.fits**, as another means of identifying it as a new eference file separate from the current DGEOFILE files. The header for this new reference file also remains very simple, as illustrated in :ref:`Appendix2`. -The two 65 x 33 arrays get read into memory with each input ACS/WFC chip (one for +Distortion residuals have been calibrated for ACS by looking at the average correction that +still needs to be applied over each 64x64 pixel section of each chip after applying +the polynomial coefficients. This +would normally result in a 64 x 32 array of residuals for each 4096 x 2048 chip. +These arrays, though, need to be expanded by one value in each dimension to support +interpolation all the way to the edge of each chip resulting in 65 x 33 arrays of +distortion correction data. Applying these corrections starts by reading the two 65 x 33 +arrays into memory with each input ACS/WFC chip WCS (one for X offsets and one for Y offsets). Bi-linear interpolation based on the input pixel position then gets used on-the-fly to extract the final offset from this reference file. Initial versions of these sub-sampled NPOLFILE reference files for ACS have -been derived from the current full-size DGEOFILEs, but testing indicates residuals -on the order of 0.02 pixels remain when compared to Jay's results. +been derived from the current full-size DGEOFILEs, and testing indicates residuals +only on the order of 0.02 pixels or less remain when compared to Jay's results. Detector To Image Correction ============================ |