CIGAL Reference Manual, Chapter 2 (Commands): SPLINE
usage: spline [vlist flag npixs delta ]
or: spline [vnum flag npixs delta ]
SPLINE smooths a vector list by making curved segments between points. SPLINE is a more sophisticated vector smoothing operation than the SMOOTH command. SMOOTH simply replaces each point with the average of its neighbors, whereas SPLINE keeps every point where it is but then makes the lines connecting the points smooth curves by making the 1st and 2nd derivatives of the curve continuous.
The arguments to SPLINE are:
VLIST the list of vectors to be SPLINEd. The default is VECS, the entire active list of stored graphics vectors. VNUM instead of VLIST you can simply specify a number that is interpreted as the number of the first vector in VECS to SPLINE; the VLIST is then all vectors from VNUM to the end of VECS. FLAG 0 - default- do not close curve or save splined vectors 1 - close curves- join first and last vectors in each list 2 - save splined vectors 3 - close curves AND save splined vectors NPIXS number of pixels between drawn points in the result (default = 3); this parameter affects the smoothness of the drawn curve. DELTA ignore vectors that move less than DELTA distance from previous point