DoLookAtFrom(3D)

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)