1TDPARA(3NCARG)                   NCAR GRAPHICS                  TDPARA(3NCARG)
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NAME

6       TDPARA - Initialization routine for TDPACK, called to set the value of
7       certain internal values.
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SYNOPSIS

10       CALL TDPARA (UA00, VA00, WA00, UV10, VV10, WV10, UV01, VV01, WV01)
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C-BINDING SYNOPSIS

13       #include <ncarg/ncargC.h>
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15       void c_tdpara(float ua00, float va00, float wa00, float uv10, float
16       vv10, float wv10, float uv01, float vv01, float wv01)
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DESCRIPTION

19       This routine may be thought of as an initialization routine or as just
20       a routine to access certain internal values; it simply transfers the
21       values of its arguments into TDPACK labelled common blocks for later
22       use by other TDPACK routines. These values define a "reference
23       parallelogram".  Each point in the plane in which the parallelogram
24       lies can be identified by specifying its "parallelogram coordinates": a
25       pair of reals, one of which may be thought of as an "X" coordinate and
26       the other of which may be thought of as a "Y" coordinate.
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28       Calls to TDPARA may be positioned without regard to calls to TDINIT
29       because the two routines do not affect one another.  Redefining the
30       reference parallelogram affects the behavior of each of the routines
31       TDPRPA, TDPRPI, TDGRID, TDLBLA, and TDPLCH, each of which makes use of
32       parallelogram coordinates in some way.  Be aware that each of the
33       routines TDGRDS and TDLBLS calls TDPARA to redefine the reference
34       parallelogram and neither of them restores the original definition when
35       it is done.
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37       If a point has "parallelogram coordinates" (XIPA,YIPA), then its actual
38       3-space coordinates are given by the following equations:
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40         U = UA00+XIPA*UV10+YIPA*UV01
41         V = VA00+XIPA*VV10+YIPA*VV01
42         W = WA00+XIPA*WV10+YIPA*WV01
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44       The point with parallelogram coordinates (0,0) is in what might be
45       thought of as the "lower left" corner of the parallelogram, while the
46       point with parallelogram coordinates (1,1) is in what might be thought
47       of as the "upper right" corner of the parallelogram. Any point of the
48       plane in which the reference parallelogram lies can be identified using
49       its parallelogram coordinates, not just the points inside the
50       parallelogram itself.
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52       Note that, although the reference parallelogram doesn't have to be
53       rectangular, a non-rectangular one is probably not very useful; in
54       fact, a square one defined by unit vectors is probably best,
55       particularly if one is drawing characters in the plane of the reference
56       parallelogram.  For example, suppose that you want to write the
57       characters "THE U/V PLANE" in that part of the U/V plane with U values
58       between 0 and 100 and V values between 0 and 200; it is probably best,
59       in this case, to use a reference parallelogram with an origin at
60       (0,0,0), an "X" side with components (1,0,0) and a "Y" side with
61       components (0,1,0).  Then, in the call to TDPLCH, one can place the
62       character string at parallelogram coordinates (50,100) and use a
63       character size of 1.5.  If one used a reference parallelogram with an
64       origin at (0,0,0), an "X" side with components (100,0,0) and a "Y" side
65       with components (0,200,0), one could place the character string at
66       parallelogram coordinates (.5,.5) and use a character size of .015, but
67       the characters written would be twice as high as they are wide, which
68       is undesirable.
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70       The arguments of TDPARA are as follows:
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72       UA00, VA00, and WA00
73               (input expressions of type REAL) - the coordinates of the
74               "origin" of the parallelogram: the point with parallelogram
75               coordinates (0,0).
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77       UV10, VV10, and WV10
78               (input expressions of type REAL) - the U, V, and W components
79               of the vector from the origin of the parallelogram to the point
80               with parallelogram coordinates (1,0).
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82       UV01, VV10, and WV01
83               (input expressions of type REAL) - the U, V, and W components
84               of the vector from the origin of the parallelogram to the point
85               with parallelogram coordinates (0,1).
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C-BINDING DESCRIPTION

88       The C-binding argument descriptions are the same as the FORTRAN
89       argument descriptions.
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ACCESS

92       To use TDPARA or c_tdpara, load the NCAR Graphics libraries ncarg,
93       ncarg_gks, and ncarg_c, preferably in that order.
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SEE ALSO

96       Online: tdclrs, tdctri, tddtri, tdgeti, tdgetr, tdgrds, tdgrid, tdgtrs,
97       tdinit, tditri, tdlbla, tdlbls, tdline, tdlnpa, tdmtri, tdotri, tdpack,
98       tdpack_params, tdplch, tdprpa, tdprpi, tdprpt, tdseti, tdsetr, tdsort,
99       tdstri, tdstrs
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102       Copyright (C) 1987-2009
103       University Corporation for Atmospheric Research
104       The use of this Software is governed by a License Agreement.
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108UNIX                               July 1997                    TDPARA(3NCARG)
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