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| author | hack <hack@stsci.edu> | 2012-09-19 11:25:26 -0400 |
|---|---|---|
| committer | hack <hack@stsci.edu> | 2012-09-19 11:25:26 -0400 |
| commit | e1d0d1818520a0ea98e25ceaba432e30fe4fb429 (patch) | |
| tree | 10181417df75fa60d4ed4829dd00b0defd8e2ebc /doc/source | |
| parent | 41caa05accff5b790e383eddcadddfc4956e635b (diff) | |
| download | stwcs_hcf-e1d0d1818520a0ea98e25ceaba432e30fe4fb429.tar.gz | |
Added more explanation about the data arrays of the NPOLFILE and the subsampling rules.
git-svn-id: http://svn.stsci.edu/svn/ssb/stsci_python/stsci_python/trunk/stwcs@19556 fe389314-cf27-0410-b35b-8c050e845b92
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 ============================ |