splines

safra · 2009-03-30 09:56:11

Hi,

I have a set of points in 3D space and want to interpolate through them smoothly over a specific timespan. I searched for spline interpolation code and found some info (http://en.wikipedia.org/wiki/Cubic_Hermite_spline) and also on this forum (http://www.mathisfunforum.com/viewtopic.php?id=4092) but can't get the grasps of it.

Anyone knows of a source with code examples?

Thanks

John E. Franklin · 2009-03-30 12:52:25

I think this is 2-D, but
might be a good source of info:
http://online.redwoods.cc.ca.us/instruct/darnold/laproj/Fall98/SkyMeg/Proj.PDF
It's over my head.
Also MATLAB's interp3 is used for 3-D.
Here is something else I found in C++:
http://elonen.iki.fi/code/tpsdemo/
You can download more code on the page.

safra · 2009-03-31 00:24:02

Thanks John, I quickly looked at the examples and it seems like a good start. But after thinking more about it I am not sure if typical spline interpolation is what I need?

Please look at the example below. Connecting 3 points results in something like in figure 1 with spline interpolation. Connecting 4 points results in something like figure 2 below. This is not what I need. In my case I am adding points constantly and I do not want the tangent (this is what it is called if I am right?) of the last added point to change (C in figure 2) . The angle at point C should remain the same like in figure 3. The rotation at point D should probably depend on the angle between BC and BD and the distance between CD. Then while interpolation over a timespan I need to find the points on the curve between each 2 points.

Is this indeed a type of Spline interpolation or is there another way to do this?

Last edited by safra (2009-03-31 00:25:46)

luca-deltodesco · 2009-03-31 04:28:51

You can very easily get a spline which will not effect any of the rest of the spline when adding a new point, but it is nigh impossible to get it form a continous smooth curve that would be acceptible.

However, if you allow for two extra control points around the spline, it is very simple using the catmull-rom or a generalisation of it, wherein adding an extra control point will draw one more segment with the rest of it being untouched

safra · 2009-03-31 20:29:59

Thanks luca-deltodesco! Found some nice code about all of this at http://actionsnippet.com/?p=1042.

Math Is Fun Forum

#1 2009-03-30 09:56:11

splines

#2 2009-03-30 12:52:25

Re: splines

#3 2009-03-31 00:24:02

Re: splines

#4 2009-03-31 04:28:51

Re: splines

#5 2009-03-31 20:29:59

Re: splines

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