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diff --git a/doc/source/updatewcs.rst b/doc/source/updatewcs.rst new file mode 100644 index 0000000..73b3840 --- /dev/null +++ b/doc/source/updatewcs.rst @@ -0,0 +1,68 @@ +.. _updatewcs: + +************************************** +UPDATEWCS +************************************** +UPDATEWCS applies corrections to the WCS of a science file +and adds reference information as header keywords and fits +file extensions so that a science file contains all necessary +information to represent astrometrically precise positions. +The order in which the corrections are applied is important +and is as follows: + +- Detector to Image Correction + +- Apply Time dependent distortion (if applciable) + +- Recomputing the basic WCS + +- Apply Velocity Aberration Correction + +- Apply polynomial distortion through the SIP coefficients + +- Apply non-polynomial distortion + +Mathematicall the entire transformation from detector to sky +coordinates is described by: + +.. math:: (x',y') &= DET2IM(x,y) + +.. math:: \binom{u'}{v'} &= \binom{x' - CRPIX1}{y' - CRPIX2} + +.. math:: \left( \begin{array}{ll} + \alpha \\ + \delta \\ + \end{array} \right) &= + \left( \begin{array}{ll} + CRVAL1 \\ + CRVAL2\\ + \end{array} \right) + + \left( \begin{array}{cc} + CD11 & CD12 \\ + CD21 & CD22\\ + \end{array} \right) + \left( \begin{array}{ll} + u' + f(u',v') + LT_x(x',y') \\ + v' + g(u',v') + LT_y(x',y') \\ + \end{array} \right) + +where f(u',v') and g(u',v') represent the polynomial distortion correction specified as + +.. math:: f(u',v') = \sum_{p+q=2}^{AORDER} A_{pq} {u'}^{p} {v'}^{q} + \\ + g(u',v') = \sum_{p+q=2}^{BORDER} B_{pq} {u'}^{p} {v'}^{q} + + +where + +* x', y' are the initial coordinates x,y with the 68th column correction applied through the DET2IM convention +* u',v' are the DET2IM-corrected coordinates relative to CRPIX1,CRPIX2 +* LT<sub>x</sub>, LT<sub>y</sub> is the residual distortion in the lookup tables written to the header using the Paper IV lookup table convention +* A, B are the SIP coefficients specified using the SIP convention + +.. toctree:: + :maxdepth: 2 + + updatewcs_ui + apply_corrections + wcs_corrections
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