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

safra
Member
Registered: 2005-12-03
Posts: 41

### splines

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

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

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

### Re: splines

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
Also MATLAB's  interp3  is used for 3-D.
Here is something else I found in C++:
http://elonen.iki.fi/code/tpsdemo/

igloo myrtilles fourmis

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

safra
Member
Registered: 2005-12-03
Posts: 41

### Re: splines

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)

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

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

### Re: splines

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

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

safra
Member
Registered: 2005-12-03
Posts: 41

### Re: splines

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

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