diff options
Diffstat (limited to 'updatewcs/corrections.py')
| -rw-r--r-- | updatewcs/corrections.py | 47 |
1 files changed, 36 insertions, 11 deletions
diff --git a/updatewcs/corrections.py b/updatewcs/corrections.py index ee73d61..2e06656 100644 --- a/updatewcs/corrections.py +++ b/updatewcs/corrections.py @@ -13,7 +13,7 @@ DGEOCorr = dgeo.DGEOCorr class TDDCorr(object): """ Apply time dependent distortion correction to distortion coefficients and basic - WCS keywords. This applies only to ACS/WFC data. + WCS keywords. This correction **must** be done before any other WCS correction. Parameters ---------- @@ -21,17 +21,34 @@ class TDDCorr(object): An HSTWCS object to be modified ref_wcs: HSTWCS object A reference HSTWCS object - + Notes ----- - Compute the ACS/WFC time dependent distortion terms - as described in [1]_. + Compute the ACS/WFC time dependent distortion terms as described + in [1]_ and apply the correction to the WCS of the observation. + + The model coefficients are stored in the primary header of the IDCTAB. + :math:`D_{ref}` is the reference date. The computed corrections are saved + in the science extension header as TDDALPHA and TDDBETA keywords. + + .. math:: TDDALPHA = A_{0} + {A_{1}*(obsdate - D_{ref})} + + .. math:: TDDBETA = B_{0} + B_{1}*(obsdate - D_{ref}) + + + The time dependent distortion affects the IDCTAB coefficients, and the + relative location of the two chips. Because the linear order IDCTAB + coefficients ar eused in the computatuion of the NPOL extensions, + the TDD correction affects all components of the distortion model. - The zero-point terms account for the skew accumulated between - 2002.0 and 2004.5, when the latest IDCTAB was delivered. - alpha = 0.095 + 0.090*(rday-dday)/2.5 - beta = -0.029 - 0.030*(rday-dday)/2.5 + Application of TDD to the IDCTAB polynomial coefficients: + The TDD model is computed in Jay's frame, while the IDCTAB coefficients + are in the HST V2/V3 frame. The coefficients are transformed to Jay's frame, + TDD is applied and they are transformed back to the V2/V3 frame. This + correction is performed in this class. + Application of TDD to the relative location of the two chips is + done in `makewcs`. References ---------- @@ -162,10 +179,18 @@ class VACorr(object): class CompSIP(object): """ - Compute SIP coefficients from IDC table coefficients. + Compute Simple Imaging Polynomial (SIP) coefficients as defined in [2]_ + from IDC table coefficients. - Notes - ----- + This class transforms the TDD corrected IDCTAB coefficients into SIP format. + It also applies a binning factor to the coefficients if the observation was + binned. + + References + ---------- + .. [2] David Shupe, et al, "The SIP Convention of representing Distortion + in FITS Image headers", Astronomical Data Analysis Software And Systems, ASP + Conference Series, Vol. 347, 2005 """ |