On Tue, 22 Nov 2005, Warren Francis wrote:
> For my purposes, I think you're right about the natural cubic splines.
> Guaranteeing that an object passes through an exact point in space will
> be more immediately useful than trying to create rules governing where
> control points ought to be placed so that the object passes close enough
> to where I intended it to go.
Right so. I wrote that code the first time when i was in a similar spot
myself - trying to draw maps with nice smooth roads etc based on a fairly
sparse set of points - so i felt your pain.
> Thanks for the insight, I never would have found that on my own. At
> least not until Google labs comes out with a search engine that gives
> names for what you're thinking of. ;-)
You're in for a wait - i think that feature's scheduled for summer 2006.
> I know this is a fairly pitiful request, since it just involves parsing
> your code, but I'm new enough to this that I'd benefit greatly from an
> couple of lines of example code, implementing your classes... how do I
> go from a set of coordinates to a Natural Cubic Spline, using your
> python code?
Pitiful but legit - i haven't documented that code at all well. If you go
right to the foot of my code, you'll find a simple test routine, which
shows you the skeleton of how to drive the code. It looks a bit like this
(this is slightly simplified):
def test_spline():
knots = [(0, 0), (0, 1), (1, 0), (0, -2), (-3, 0)] # a spiral
trace = []
c = NaturalCubicSpline(tuples2points(knots))
u = 0.0
du = 0.1
lim = len(c) + du
while (u < lim):
p = c(u)
trace.append(tuple(p))
u = u + du
return trace
tuples2points is a helper function which turns your coordinates from a
list of tuples (really, an iterable of length-2 iterables) to a list of
Points. The alternative way of doing it is something like:
curve = NaturalCubicSpline()
for x, y in knot_coords:
curve.knots.append(Point(x, y))
do_something_with(curve)
tom
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