VARKON Version 1.17 1999-10-21

cur_usrdef - Geometric procedure

Creates a curve
 

Description

Low level routine to create a rational or non rational cubic parametric curve by specifying the polynomial coefficients for all segments. Each segment is defined by 16 values orderd in a 4 by 4 matrix. By specifying an optional surface-id the curve becomes an UV-curve, ie. a curve on the surface (in the UV-plane of the surface). The four basic polynomials for a rational segment are:

x(t) = c0x + c1x*t + c2x*t*t + c3x*t*t*t
y(t) = c0y + c1y*t + c2y*t*t + c3y*t*t*t
z(t) = c0z + c1z*t + c2z*t*t + c3z*t*t*t
w(t) = c0w + c1w*t + c2w*t*t + c3w*t*t*t

For a given segment i the order of the coefficients in segdat should be:

segdat(i,1,1) = c0x segdat(i,2,1) = c1x segdat(i,3,1) = c2x segdat(i,4,1) = c3x
segdat(i,1,2) = c0y segdat(i,2,2) = c1y segdat(i,3,2) = c2y segdat(i,4,2) = c3y
segdat(i,1,3) = c0z segdat(i,2,3) = c1z segdat(i,3,3) = c2z segdat(i,4,3) = c3z
segdat(i,1,4) = c0w segdat(i,2,4) = c1w segdat(i,3,4) = c2w segdat(i,4,4) = c3w

Syntax

cur_usrdef(id, nseg, segdat, sur_id:attributes);
 
 

REF	id;
INT	nseg;
FLOAT	segdat(nseg,4,4);
REF	sur_id;

Principal parameters
 
 

id	- Local identity
nseg	- Number of segments
segdat	- Segment coefficients

Optional parameters
 
 

sur_id

- Identity of a surface

Attributes
 
 

PEN	- Pen or colour number
LEVEL	- Level number
BLANK	- Visible(0) or invisible(1)
CFONT	- Solid(0), dashed(1) or centerline(2)
CDASHL	- Dashlength
WIDTH	- Linewidth

Comments

If a non rational segment is wanted c0w should be set to 1.0 and c1w,c2w,c3w to 0.0.

If a curve on a surface is wanted ( a UV-curve) use the optional parameter sur_id to specify the identity of the surface.

When creating a UV-curve you need to specify the curve in the varkon internal parameter space.
Example: a one patch surface does in mbs have parameters 0 < u < 1 and 0 <= v <= 1, but internaly the parameter spans are 1 < u < 2 and 1 <= v <= 2. For a nurbs surface the internal parameter spans are defined by the knot vecktors.