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

6       TDINIT - Initialization routine for TDPACK, called to define the
7       position of the eye, the position of the point looked at, which way is
8       up, and whether or not a stereo view is to be done.
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SYNOPSIS

11       CALL TDINIT (UMID, VMID, WMID, UORI, VORI, WORI, UTHI, VTHI, WTHI,
12       OTEP)
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C-BINDING SYNOPSIS

15       #include <ncarg/ncargC.h>
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17       void c_tdinit(float umid, float vmid, float wmid, float uori, float
18       vori, float wori, float uthi, float vthi, float wthi, float otep)
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DESCRIPTION

21       This initialization routine is called to define the position of the
22       eye, the position of the point looked at, which way is up, and whether
23       or not a stereo view is to be done. TDINIT precomputes some quantities
24       in TDPACK common blocks that will subsequently be used in projecting
25       points from 3-space (U, V, and W coordinates) to 2-space (X and Y
26       coordinates).
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28       By default (that is to say, if the internal parameter 'SET' has its
29       default value), TDINIT also calls the SPPS routine SET to define the
30       mapping from the "user" coordinate system (the X/Y system) to the
31       "fractional" coordinate system (in GKS terms, NDC space). This is done
32       in such a way as to show in the projection plane a field of view of
33       'FOV' degrees.  The viewport to be used in the fractional coordinate
34       system is that defined by the values of the internal parameters 'VPL',
35       'VPR', 'VPB', and 'VPT'. In some situations, it may be desirable, after
36       calling TDINIT, to call the SPPS routine GETSET to retrieve the
37       arguments with which TDINIT called SET and then recall SET with a
38       different set of arguments.
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40       Normally, the creation of an image with TDPACK starts with a call to
41       TDINIT (perhaps preceded by calls to TDSETI, TDSETR, and/or TDSTRS to
42       reset internal parameters of the package) and continues with calls to
43       draw objects. (Of course, if all of the arguments in a call to TDINIT
44       have the same values as in the last call and the SET call that was done
45       as a result is still in effect, then it's not necessary to repeat the
46       call to TDINIT.)
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48       For stereo views, one calls TDINIT with a negative OTEP, executes the
49       object-drawing calls, calls TDINIT again with a positive OTEP, and then
50       repeats all of the object-drawing calls. The exact way in which stereo
51       views are drawn is also affected (slightly) by the value of the
52       internal parameter 'STE'.
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54       The arguments of TDINIT are as follows:
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56       UMID, VMID, and WMID
57               (input expressions of type REAL) - the coordinates of a point,
58               E, at the eye position (if a single view is being drawn), or of
59               a point midway between the two eyes (if a stereo view is being
60               drawn).
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62       UORI, VORI, and WORI
63               (input expressions of type REAL) - the coordinates of a point,
64               O, that the eye is looking at.  That point defines the origin
65               of the XY projection plane.  The line of sight is the line from
66               E to O.  The projection plane passes through O and is
67               perpendicular to the line of sight.
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69       UTHI, VTHI, and WTHI
70               (input expressions of type REAL) - the coordinates of a third
71               point, T, needed to completely specify the orientation of the X
72               and Y axes in the projection plane.  The Y axis of the
73               projection plane is its intersection with the plane passing
74               though the points E, O, and T.  The X axis of the projection
75               plane passes through the point O and is perpendicular to the Y
76               axis.
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78       OTEP    (an input expression of type REAL) - set non-zero if and only
79               if a stereo view is to be drawn.  Make the value negative to
80               draw a left-eye view, positive to draw a right-eye view.  The
81               magnitude of OTEP is the distance from either eye to the point
82               midway between the eyes; if R represents the approximate
83               distance from the eye to the objects being drawn, then OTEP may
84               be set using a statement like
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86                 OTEP = (+ or -) R *
87                        TAN(.017453292519943*ANGD/2.)
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89               where the constant (.01745...) is just pi/180 and ANGD is the
90               desired difference in the angle between the two views, in
91               degrees; use a value of about 1 or 2 degrees for ANGD.
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93               Note that, if the origin is approximately in the middle of the
94               objects being viewed, then it's probably appropriate to use a
95               value of R computed as follows:
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97                 R = SQRT((UMID-UORI)**2
98                          (VMID-VORI)**2+
99                          (WMID-WORI)**2)
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C-BINDING DESCRIPTION

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

106       To use TDINIT or c_tdinit, load the NCAR Graphics libraries ncarg,
107       ncarg_gks, and ncarg_c, preferably in that order.
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SEE ALSO

110       Online: tdclrs, tdctri, tddtri, tdgeti, tdgetr, tdgrds, tdgrid, tdgtrs,
111       tditri, tdlbla, tdlbls, tdline, tdlnpa, tdmtri, tdotri, tdpack,
112       tdpack_params, tdpara, tdplch, tdprpa, tdprpi, tdprpt, tdseti, tdsetr,
113       tdsort, tdstri, tdstrs
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116       Copyright (C) 1987-2009
117       University Corporation for Atmospheric Research
118       The use of this Software is governed by a License Agreement.
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122UNIX                               July 1997                    TDINIT(3NCARG)
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