NAME

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

SYNOPSIS

       CALL TDINIT (UMID, VMID, WMID, UORI, VORI, WORI, UTHI, VTHI, WTHI, OTEP)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_tdinit(float umid, float vmid, float wmid, float uori, float vori, float wori, float uthi, float
       vthi, float wthi, float otep)

DESCRIPTION

       This initialization routine is called to define the position of the eye, the position of the point looked
       at, which way is up, and whether or not a stereo view is to be done. TDINIT precomputes some quantities
       in TDPACK common blocks that will subsequently be used in projecting points from 3-space (U, V, and W
       coordinates) to 2-space (X and Y coordinates).

       By default (that is to say, if the internal parameter 'SET' has its default value), TDINIT also calls the
       SPPS routine SET to define the mapping from the "user" coordinate system (the X/Y system) to the
       "fractional" coordinate system (in GKS terms, NDC space). This is done in such a way as to show in the
       projection plane a field of view of 'FOV' degrees.  The viewport to be used in the fractional coordinate
       system is that defined by the values of the internal parameters 'VPL', 'VPR', 'VPB', and 'VPT'. In some
       situations, it may be desirable, after calling TDINIT, to call the SPPS routine GETSET to retrieve the
       arguments with which TDINIT called SET and then recall SET with a different set of arguments.

       Normally, the creation of an image with TDPACK starts with a call to TDINIT (perhaps preceded by calls to
       TDSETI, TDSETR, and/or TDSTRS to reset internal parameters of the package) and continues with calls to
       draw objects. (Of course, if all of the arguments in a call to TDINIT have the same values as in the last
       call and the SET call that was done as a result is still in effect, then it's not necessary to repeat the
       call to TDINIT.)

       For stereo views, one calls TDINIT with a negative OTEP, executes the object-drawing calls, calls TDINIT
       again with a positive OTEP, and then repeats all of the object-drawing calls. The exact way in which
       stereo views are drawn is also affected (slightly) by the value of the internal parameter 'STE'.

       The arguments of TDINIT are as follows:

       UMID, VMID, and WMID
               (input  expressions  of  type  REAL)  -  the coordinates of a point, E, at the eye position (if a
               single view is being drawn), or of a point midway between the two eyes (if a stereo view is being
               drawn).

       UORI, VORI, and WORI
               (input expressions of type REAL) - the coordinates of a point, O, that the  eye  is  looking  at.
               That  point  defines the origin of the XY projection plane.  The line of sight is the line from E
               to O.  The projection plane passes through O and is perpendicular to the line of sight.

       UTHI, VTHI, and WTHI
               (input expressions of type REAL) - the coordinates of a third  point,  T,  needed  to  completely
               specify  the  orientation  of  the  X  and  Y  axes  in  the projection plane.  The Y axis of the
               projection plane is its intersection with the plane passing though the points E, O, and T.  The X
               axis of the projection plane passes through the point O and is perpendicular to the Y axis.

       OTEP    (an input expression of type REAL) - set non-zero if and only if a stereo view is  to  be  drawn.
               Make  the  value  negative  to  draw  a  left-eye  view,  positive to draw a right-eye view.  The
               magnitude of OTEP is the distance from either eye to the point midway  between  the  eyes;  if  R
               represents the approximate distance from the eye to the objects being drawn, then OTEP may be set
               using a statement like

                 OTEP = (+ or -) R *
                        TAN(.017453292519943*ANGD/2.)

               where  the  constant  (.01745...)  is just pi/180 and ANGD is the desired difference in the angle
               between the two views, in degrees; use a value of about 1 or 2 degrees for ANGD.

               Note that, if the origin is approximately in the middle of the objects being  viewed,  then  it's
               probably appropriate to use a value of R computed as follows:

                 R = SQRT((UMID-UORI)**2
                          (VMID-VORI)**2+
                          (WMID-WORI)**2)

C-BINDING DESCRIPTION

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

ACCESS

       To  use TDINIT or c_tdinit, 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, tditri, tdlbla,  tdlbls,  tdline,
       tdlnpa,  tdmtri,  tdotri,  tdpack, tdpack_params, tdpara, 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.

UNIX                                                July 1997                                     TDINIT(3NCARG)