ASTRD2XY

Name

astrd2xy

Purpose

Astrometry conversion from ($\alpha$,$\delta$) to image (x,y)

Description

This transformation can either be based on a simple linear transformation
with rotation from the celestial sphere to linear CCD chip coordinates.
Or, it can use a full astrometric solution (including linear).

Calling Sequence

astrd2xy,ra,dec,info,x,y

Inputs

ra - Right ascension (radians)
dec - Declination (radians)
info - Transformation information held in an anonymous structure. There
are two different groups of tags that can appear. The original
simple linear transformation needs the following tags:
pscale - Plate scale (arcsec/pixel).
rang - Rotation angle of image (radians).
xflip - -1 if image flipped in X, 1 if not.
yflip - -1 if image flipped in Y, 1 if not.
The full-up transformation requires a different set of tags:
renormfac - normalization factor
cxi - xi transformations coefficients (x,y -> xi)
ceta - eta transformations coefficients (x,y -> eta)
terms - string array with names of terms to fit
Both types need the following.
xcref - X center of image.
ycref - Y center of image.
raref - Right ascension of center of image (tangent plane).
decref - Declination of center of image (tangent plane).

Optional Input Parameters

Keyword Input Parameters

FULL - Flag, if set indicates the full transformation should be used.
Only the tags needed must be provided.

Outputs

x - X coordinate in image
y - Y coordinate in image

Keyword Output Parameters

Common Blocks

Side Effects

Restrictions

Procedure

Modification History

1997/04/05 - Written by Marc W. Buie, Lowell Observatory
2009/06/21, MWB added full-up transformation
2009/11/02, MWB, split off most of code into astsn2xy