1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
|
.help unpcd Jun99 "Slalib Package"
.nf
SUBROUTINE slUPCD (DISCO,X,Y)
- - - - - -
U P C D
- - - - - -
Remove pincushion/barrel distortion from a distorted [x,y]
to give tangent-plane [x,y].
Given:
DISCO d pincushion/barrel distortion coefficient
X,Y d distorted coordinates
Returned:
X,Y d tangent-plane coordinates
Notes:
1) The distortion is of the form RP = R*(1 + C*R**2), where R is
the radial distance from the tangent point, C is the DISCO
argument, and RP is the radial distance in the presence of
the distortion.
2) For pincushion distortion, C is +ve; for barrel distortion,
C is -ve.
3) For X,Y in "radians" - units of one projection radius,
which in the case of a photograph is the focal length of
the camera - the following DISCO values apply:
Geometry DISCO
astrograph 0.0
Schmidt -0.3333
AAT PF doublet +147.069
AAT PF triplet +178.585
AAT f/8 +21.20
JKT f/8 +13.32
4) The present routine is an approximate inverse to the
companion routine slPCD, obtained from two iterations
of Newton's method. The mismatch between the slPCD and
slUPCD routines is negligible for astrometric applications;
to reach 1 milliarcsec at the edge of the AAT triplet or
Schmidt field would require field diameters of 2.4 degrees
and 42 degrees respectively.
P.T.Wallace Starlink 1 August 1994
Copyright (C) 1995 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
|
