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*The graPHIGS Programming Interface: ISO PHIGS Subroutine Reference*

## EVALUATE VIEW ORIENTATION MATRIX 3 (PHOP,*,*,*)

**Purpose**

Use
Evaluate View Orientation Matrix 3
to calculate a three-dimensional
viewing matrix based on the specified
orientation.

The matrix returned performs a change from
the World Coordinate (WC) system to a
Viewing Coordinate (VC) system in which the origin is the
view reference point, the n-axis is the
view plane normal, and the v-axis lies in
the half plane designated by the view up vector.

If the graPHIGS API can compute the view orientation matrix,
then the graPHIGS API sets the error indicator to zero and
returns the view orientation matrix.
If the graPHIGS API cannot compute the view orientation matrix,
then the values of the matrix are unpredictable
and the graPHIGS API sets the error indicator to one of the
following errors:

**2**
- Function Requires State (PHOP,*,*,*)
**159**
- View Plane Normal Vector Has Length Zero
**160**
- View UP Vector Has Length Zero
**161**
- View UP AND View Plane Normal Vectors Are Parallel

**Language Bindings**

#### C

**peval_view_ori_matrix3**
(*view_ref_point, view_norm_vec,
view_up_vec, err_ind, result_tran*) |

*const Ppoint3 *view_ref_point*View reference point in WC.
*const Pvec3 *view_norm_vec*View plane normal vector in WC.
*const Pvec3 *view_up_vec*View up vector in WC.

*Pint *err_ind*Error indicator.
*Pmatrix3 result_tran*View orientation matrix.
(See
Chapter 15. "ISO PHIGS Transformations" for a description
of the storage of the transformation matrix).
#### FORTRAN

**PEVOM3**
(*vwrx*, *vwry*, *vwrz*,
*vpnx*, *vpny*, *vpnz*,
*vupx*, *vupy*, *vupz*,
*errind*, *vwormt*) |

*real vwrx**x* coordinate of the view reference point in WC.
*real vwry**y* coordinate of the view reference point in WC.
*real vwrz**z* coordinate of the view reference point in WC.
*real vpnx*x-axis directional component of the view plane normal in WC.
*real vpny*y-axis directional component of the view plane normal in WC.
*real vpnz*z-axis directional component of the view plane normal in WC.
*real vupx*x-axis directional component of the view up vector in WC.
*real vupy*y-axis directional component of the view up vector in WC.
*real vupz*z-axis directional component of the view up vector in WC.

*integer errind*Error indicator.
*real vwormt(4,4)*View orientation matrix.
(See
Chapter 15. "ISO PHIGS Transformations" for a description
of the storage of the transformation matrix).
**Errors**

None

**Related Subroutines**

None

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