Using csaps (or similar) to create a 3D smoothing spline

I have a series of 3D points and am looking to create any sort of smoothing spline, I was hoping to use scaps, but it only seems to take in 2D data, can anyone help with this? Is there for instance a way to input 3D data into it or another function I could use?

Answer 1

[Dasharath Gulvady]

You can do this using "csaps" function. However the trick is to make "z" your independent variable.

[pp,p]=csaps(z,[x;y]);
val=fnval(pp,z);
figure,plot3(x,y,z);
hold on,plot3(val(1,:),val(2,:),z,'r-')
grid on

[Laurence hutton-smith]

Thank you, this is extremely helpful.

Answer 2

[Bryan Howell]

The accepted answer is quite elegant but doesn't work for all types of trajectories, especially those where the z value is relatively constant.

An alternative approach is to fit a smoothing spline for each dimension and then combine. For example...

% given data in a point matrix, xyz, which is 3 x number of points
[ndim,npts]=size(xyz);
xyzp=zeros(size(xyz));
for k=1:ndim
   xyzp(k,:)=ppval(csaps(1:npts,xyz(k,:)),1:npts);
end

This approach is also not a panacea but can address some cases where the first answer might fail.