NAME

       SET3 - Defines the transformation from three dimensions to two dimensions.

SYNOPSIS

       CALL SET3 (XMIN,XMAX,YMIN,YMAX,UMIN,UMAX,VMIN,VMAX,WMIN,WMAX,PEYE)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_set3 (float xmin, float xmax, float ymin, float ymax,
       float umin, float umax, float vmin, float vmax, float wmin,
       float wmax, float peye[3])

DESCRIPTION

       XMIN,XMAX,YMIN,YMAX
                   (input  expressions  of  type  REAL)  are  the  fractional coordinates (in NDCs) defining the
                   portion of the plotter frame (the "viewport") into which 3-D objects  are  to  be  projected.
                   Each  has  a  value between 0. and 1., inclusive.  Examples:  To use the whole plotter frame,
                   set XMIN=0., XMAX=1., YMIN=0., and YMAX=1.; to use the upper  left  quarter  of  the  plotter
                   frame, set XMIN=0., XMAX=.5, YMIN=.5, and YMAX=1.

       UMIN,UMAX,VMIN,VMAX,WMIN,WMAX
                   (input  expressions  of type REAL) are the limiting coordinates, in a 3-D coordinate space of
                   the user's choosing, of the rectangular box that is  to  be  projected.   This  box  normally
                   contains all of the objects whose projections are to be drawn.

       PEYE        (an  input array, dimensioned 3, of type REAL) is an array specifying the coordinates, in the
                   user's 3-D coordinate system, of the eye position.  The point

                         (PEYE(1),PEYE(2),PEYE(3))

                   must be outside the box defined by UMIN, UMAX, VMIN, VMAX, WMIN, and WMAX.  Objects  will  be
                   drawn as they appear from this point.

       The call to SET3 says what portion of the 3-D coordinate system is to be projected, from what point it is
       to be projected, and where the resulting picture is to be placed on the plotter frame.

       The array PEYE specifies the position of the eye, which may be referred to as the "viewpoint" or "center"
       of the projection.

       The "line of sight" runs from the point

             (PEYE(1),PEYE(2),PEYE(3))

       (the eye position) to the point

             (.5*(UMIN+UMAX),.5*(VMIN+VMAX),.5*(WMIN+WMAX))

       (the point at the center of the projected box).

       The  "image  plane"  is  perpendicular  to the line of sight and may be thought of as passing through the
       center of the box.  The projection of an arbitrary point P in 3-space is the  point  where  the  straight
       line  from  the  eye  position to P passes through the image plane.  The projection of a more complicated
       object is just the union of the projections of its constituent points.

       The projection in the image plane of the box specified by the arguments UMIN, UMAX, VMIN, VMAX, WMIN, and
       WMAX will be scaled to fit in the viewport specified by the arguments XMIN, XMAX, YMIN,  and  YMAX.   The
       projected  box  will  retain  its  natural aspect ratio; typically, it will just touch the left and right
       edges of the viewport, or the top and bottom of the viewport, but not both.

       The image of the box will be rotated so that the projection of a unit vector based at the center  of  the
       box  and  pointing  in the direction of the positive W axis will be made to point upward in the viewport.
       However, if the line of sight is very nearly parallel to the W axis, so that the projection of this  unit
       vector  shrinks  almost to a point, then a unit vector based at the center of the box and pointing in the
       direction of the positive V axis will be made to point upward in the viewport instead.   One  implication
       of  this  is  that, if you are making a movie by letting the eye "fly around" the objects being projected
       and it gets too close to being directly above or below the center of the  box,  there  may  be  a  sudden
       disconcerting rotation of the projected image.

C-BINDING DESCRIPTION

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

USAGE

       SET3 should be called before calling other THREED routines.

EXAMPLES

       Use the ncargex command to see the following relevant examples: tpwrzt, tthree.

ACCESS

       To use SET3 or c_set3, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that
       order.

SEE ALSO

       Online:  threed, curve3, fence3, frst3, line3, perim3, point3, psym3, pwrz, pwrzt, threed, tick3, tick43,
       vect3, ncarg_cbind.

       Hardcopy: NCAR Graphics Fundamentals, UNIX Version

COPYRIGHT

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

UNIX                                               March 1993                                       SET3(3NCARG)