NAME

DoLookAtFrom − Create an orienting geometric transformation object

SYNOPSIS

C:

DtObject DoLookAtFrom(at, from, up)
DtPoint3 at, from;
DtVector3 up;

FORTRAN:

INTEGER∗4 DOLAF(AT, FROM, UP)
REAL∗8 AT(3), FROM(3)
REAL∗8 UP(3)

DESCRIPTION

DoLookAtFrom creates a geometric transformation object that modifies the current transformation matrix.  DoLookAtFrom specifies a modeling transformation that combines a translation and a series of rotations. 

The parameter from specifies the position of the new origin.  The ray between at and from specifies the new Z-direction.  The new XY-plane will be the plane which is perpendicular to the new Z-direction and which includes the new origin. 

The parameter up specifies the new Y-direction as the projection of the up vector onto the new XY-plane.  The new X-direction is computed such that the new X-, Y-, and Z-directions define a right-handed coordinate system. 

DoLookAtFrom commonly specifies the position, direction of gaze, and the up direction of light and camera objects in a definition group.  It may also be used to orient primitive objects within a scene. 

ERRORS

The results of DoLookAtFrom are undefined if

The at and from points lie in a line parallel to the up vector. 

The at and from points are identical. 

The up vector is of 0 length. 

[WARNING - degenerate lookatfrom specification]

SEE ALSO

DoCamera(3D), DoLight(3D), DoRotate(3D), DoScale(3D), DoShear(3D), DoTransformMatrix(3D), DoTranslate(3D)

September 02, 1992