COMPUTE FILL AREA (SET) GEOMETRIC NORMAL 3

PCFAN3

CALL SEQUENCE

CALL PCFAN3 ( NFAS, IXA, PXA, PYA, PZA, ERRIND, NX, NY, NZ )

INPUT PARAMETERS

INTEGER NFAS

Number of vertex lists

INTEGER IXA(NFAS)

Number of vertices for each vertex list

REAL PXA(*), PYA(*), PZA(*)

Coordinates of vertices

OUTPUT PARAMETERS

INTEGER ERRIND

Error indicator

REAL NX, NY, NZ

Coordinates of geometric unit normal

EFFECT

This function returns the unit geometric normal to the given Fill Area Set.

The input data structure contains a list of vertex points which are used for the unit geometric normal calculation.

Calculating the Normal

The first three non-collinear points in the data structure, as determined below, are designated A, B, and C. The geometric normal is computed as the cross product of two vectors: the vector from A to B, and the vector from A to C; it is then reduced to unit length.

When calculating the normal for a fill area set, point A is the first point in the first fill area set boundary, point B is the first point in the fill area set boundary which is not identical to point A, and point C is the first point in the fill area set boundary which is not collinear with points A and B. This process is applied to each successive boundary in the set until a triplet is found or all boundaries have been exhausted. If no such triplet exists, Error Indicator is set to a non-zero value, and Geometric Unit Normal is undefined.

Error Indicator will return one of the following values:

0
No error

505
Warning, the fill area is degenerate.

The normal returned may be combined with the existing vertices to create a more complete specification for a Fill Area Set 3 With Data. See Fill Area Set 3 With Data (routine PFAS3D) for details.

ERRORS

1

Ignoring function, function requires state PHOP.

SEE ALSO

Fill area set 3 with data, see PFAS3D