Namespace FitsModel.Wcs

Classes

WcsConstants

The keywords given below constitute a complete set of fun- damental attributes for a WCS description.Although their inclu- sion in an HDU is optional, FITS writers should include a com- plete set of keywords when describing a WCS.In the event that some keywords are missing, default values must be assumed, as specified below.

WcsData

Representations of the mapping between image coordinates and physical(i.e., world) coordinate systems(WCSs) may be repre- sented within FITS HDUs.

Rather than store world coordinates separately for each datum, the regular lattice structure of a FITS image offers the possibil- ity of defining rules for computing world coordinates at each point.As stated in Sect. 3.3.2 and depicted in Fig. 1, image ar- ray data are addressed via integral array indices that range in value from 1 to NAXISj on Axis j.Recognizing that image data values may have an extent, for example an angular separation, spectral channel width or time span, and thus that it may make sense to interpolate between them, these integral array indices may be generalized to floating-point pixel coordinates. Integral pixel-coordinate values coincide with the corresponding array indices, while fractional pixel-coordinate values lie between ar- ray indices and thus imply interpolation.Pixel-coordinate val- ues are defined at all points within the image lattice and outside it (except along conventional axes, see Sect. 8.5). They form the basis of the world-coordinate formalism in FITS depicted schematically in Fig. 2.