- NAME
TNX_EVAL
- PURPOSE
Compute distorted coordinates given TNX (Tangent + Iraf tnx
distortion polynomial) coefficients.
- EXPLANATION
See http://fits.gsfc.nasa.gov/registry/tnx.html for the TNX convention
This distortion convention is used by IRAF.
The coefficients and information are passed via common block. This is because this
routine is called by the intrinisc BROYDEN() function in AD2XY, and
common blocks are the only way to pass parameters to the user supplied
function in BROYDEN().
- CALLING SEQUENCE
res = TNX_EVAL(xy)
- INPUTS
xy - 2 elements vector giving the undistorted X,Y position
- OUTPUTS
res - 2 element vector giving the distorted position
- COMMON BLOCKS
common broyden_coeff,pv1,pv2
pv1, pv2 are both structures giving the TNX coefficients. The
pv1/pv2 naming convention is a hangover from tpv_eval.pro on
which this approach is heavily based.
pv1.functype gives the TNX function type. Only type 3
(polynominal) is supported.
pv1.xterms gives the type of cross-terms (1: full, 2: half, 0: none)
pv1.etaorder gives the order in eta
pv1.xiorder gives the order in xi
pv1.coeff gives the actual coefficients.
- REVISION HISTORY
Written M. Sullivan Mar 2014