VARKON Version 1.15 1997-10-24

getseg - Procedure

Get curve segment from GM


Description

Reads a geometric or graphic curve segment from GM.

Syntax

getseg(curve_id, segnum, rep, segdata, offset, type, subtype, surfid_1, surfid_2)

REF	curve_id;
INT	segnum;
INT	rep;
FLOAT	segdata(4,4);
FLOAT	offset;
INT	type;
INT	subtype;
REF	surfid_1;
REF	surfid_2;

Principal parameters

id	- Global identity of a curve
segnum	- The segment to read, first segment = 1
rep	- 0 = Read geometric segment, 1 = Read graphic segment
segdata	- A 4 by 4 matrix with polynomial coefficients
offset	- Offset
type	- 1 = Rational cubic segment, 2 = UV-segment

Optional parameters

subtype	- Always 0 for a rational cubic segment. 1 for an UV-segment that lies on one surface
	2 for an UV-segment that lies on two surfaces (intersect curve)
surfid_1	- Identity of first surface if subtype = 1 or 2
surfid_2	- Identity of second surface if subtype = 2

Comments

Each segment is a rational cubic with 0 to 1 parametrisation and the coefficients ordered as follows:

k0x k0y k0z k0w
k1x k1y k1z k1w
k2x k2y k2z k2w
k3x k3y k3z k3w

Se for example Faux and Pratt, "Computational Geometry for design and manufacture", page 144 for a further discussion on rational cubic parametric segments.

Graphical segments and geometric segments can be the same thing since many curves use their geometric representation also for graphics. In that case an attempt to read graphical segment number n will simply return geometrical segment number n.