Vis Distortion Model Product¶
Metadata¶
Data product name |
DpdVisDistortionModel |
Data product custodian |
VIS |
Name of the Schema file |
|
Processing Element(s) creating/using the data product |
Astrometry |
Processing function using the data product |
VIS |
Proposed for inclusion in EAS/SAS¶
Yes
Data product elements¶
Header |
object of type sys:genericHeader |
Data |
object of type vis:visDistortionModel |
QualityFlags |
object of type dqc:sqfPlaceHolder |
Parameters |
object of type ppr:genericKeyValueParameters |
Detailed description of the data product¶
Simple world coordinate system containing a basic linear transformation from detector location to world coordinates, but images often contain higher-level distortion which we ideally want to correct. Distortion in astronomical images is introduced by some combination of the atmosphere, the telescope, and the detector. The atmosphere won’t be a problem for Euclid unless things go badly wrong. This leaves distortion due to the telescope optics, and the detector. For ground-based instruments the detector is usually mounted to the telescope via a rotator, meaning distortion can be a function of both focal plane location and detector location. For Euclid the detector is fixed with respect to the focal plane, for this reason WCSFIT uses the SIP convention to model distortion in VIS images, as opposed to the alternative TPV convention. TPV models distortion as a function of equatorial tangent plane location, where SIP models distortion as a function of detector location
Distortion Model product references a special config file to describe the distortion model for all CCD’s including givin the coordinates. Example of an output config is given below.
Assumption The main assumption we have made is that distortion and detector layout (including position, rotation, shear, stretch, reflection) remain constant between observations. Or at least between observations since the previous calibration run. I.e. that the only thing that changes astrometrically between two observations is where the instrument is pointing and its position angle. In practice this assumption is likely to be true only for low level distortion. It is anticipated that higher order distortions will be introduced due to e.g. thermal variation. It is anticipated that the modelling of such higher order distortions will be undertaken in future versions of WCSFIT.
Detailed TechNote can be found here: https://euclid.roe.ac.uk/attachments/download/75548/wcsfit_euclid_docs-1.pdf
Name of file:
EUC_VIS_MDL-DIS-000-000000-0000000__[YYYYMMDDThhmmss.s]Z.conf
where the date is the production date.