To place the piece of furniture inside the room, a segment transformation
   must be applied to the new segment.  The program uses the point returned
   by the locator input to compute a shift vector that does this.  You enter
   a shift vector for the transformation as a relative displacement value
   from a fixed point.  In this case, the new segment is located at the
   origin (0,0).  The shift vector should then be the locator point less the
   dimensions of the furniture itself.

          EVALUATE TRANSFORMATION MATRIX (0.0, 0.0,
               xcor-furnwidth, ycor-furnheight, 0.0, 1.0,
               1.0, 0, matrix1)
          SET SEGMENT TRANSFORMATION (segment name, matrix1)
          SET VISIBILITY (segment name, 1)