NAME

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

SYNOPSIS

       CALL TDPARA (UA00, VA00, WA00, UV10, VV10, WV10, UV01, VV01, WV01)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_tdpara(float ua00, float va00, float wa00, float uv10, float vv10, float wv10,
       float uv01, float vv01, float wv01)

DESCRIPTION

       This routine may be thought of as an initialization routine or as just a routine to access
       certain internal values; it simply transfers the values of its arguments into TDPACK
       labelled common blocks for later use by other TDPACK routines. These values define a
       "reference parallelogram".  Each point in the plane in which the parallelogram lies can be
       identified by specifying its "parallelogram coordinates": a pair of reals, one of which
       may be thought of as an "X" coordinate and the other of which may be thought of as a "Y"
       coordinate.

       Calls to TDPARA may be positioned without regard to calls to TDINIT because the two
       routines do not affect one another.  Redefining the reference parallelogram affects the
       behavior of each of the routines TDPRPA, TDPRPI, TDGRID, TDLBLA, and TDPLCH, each of which
       makes use of parallelogram coordinates in some way.  Be aware that each of the routines
       TDGRDS and TDLBLS calls TDPARA to redefine the reference parallelogram and neither of them
       restores the original definition when it is done.

       If a point has "parallelogram coordinates" (XIPA,YIPA), then its actual 3-space
       coordinates are given by the following equations:

         U = UA00+XIPA*UV10+YIPA*UV01
         V = VA00+XIPA*VV10+YIPA*VV01
         W = WA00+XIPA*WV10+YIPA*WV01

       The point with parallelogram coordinates (0,0) is in what might be thought of as the
       "lower left" corner of the parallelogram, while the point with parallelogram coordinates
       (1,1) is in what might be thought of as the "upper right" corner of the parallelogram. Any
       point of the plane in which the reference parallelogram lies can be identified using its
       parallelogram coordinates, not just the points inside the parallelogram itself.

       Note that, although the reference parallelogram doesn't have to be rectangular, a non-
       rectangular one is probably not very useful; in fact, a square one defined by unit vectors
       is probably best, particularly if one is drawing characters in the plane of the reference
       parallelogram.  For example, suppose that you want to write the characters "THE U/V PLANE"
       in that part of the U/V plane with U values between 0 and 100 and V values between 0 and
       200; it is probably best, in this case, to use a reference parallelogram with an origin at
       (0,0,0), an "X" side with components (1,0,0) and a "Y" side with components (0,1,0).
       Then, in the call to TDPLCH, one can place the character string at parallelogram
       coordinates (50,100) and use a character size of 1.5.  If one used a reference
       parallelogram with an origin at (0,0,0), an "X" side with components (100,0,0) and a "Y"
       side with components (0,200,0), one could place the character string at parallelogram
       coordinates (.5,.5) and use a character size of .015, but the characters written would be
       twice as high as they are wide, which is undesirable.

       The arguments of TDPARA are as follows:

       UA00, VA00, and WA00
               (input expressions of type REAL) - the coordinates of the "origin" of the
               parallelogram: the point with parallelogram coordinates (0,0).

       UV10, VV10, and WV10
               (input expressions of type REAL) - the U, V, and W components of the vector from
               the origin of the parallelogram to the point with parallelogram coordinates (1,0).

       UV01, VV10, and WV01
               (input expressions of type REAL) - the U, V, and W components of the vector from
               the origin of the parallelogram to the point with parallelogram coordinates (0,1).

C-BINDING DESCRIPTION

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

ACCESS

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

SEE ALSO

       Online: tdclrs, tdctri, tddtri, tdgeti, tdgetr, tdgrds, tdgrid, tdgtrs, tdinit, tditri,
       tdlbla, tdlbls, tdline, tdlnpa, tdmtri, tdotri, tdpack, tdpack_params, tdplch, tdprpa,
       tdprpi, tdprpt, tdseti, tdsetr, tdsort, tdstri, tdstrs

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.