[question] Interpolating closed spline ?

[4rzael]

Hello,

Is this library able to interpolate a closed spline curve ?

Thanks

[ttk592]

The library lacks the ability to set the periodic boundary condition f'(a) = f'(b) which we would need for a closed curve which is smooth at the point where it connects. However, with a small workaround it can still be achieved as a reasonable approximation, see examples/plot_parametric.cpp. E.g. the below draws something resembling an inf sign:

$ ./plot_parametric.sh -x 0 0 1 2 2 1 -y 0 1 0.5 0 1 0.5 -c

The correct way to do it:

• define a time grid points, e.g. T[i+1]=T[i]+distance(X[i],Y[i], X[i+1],Y[i+1]).
• set splines for x and y grid points: sx.set_points(T,X); and sy.set_points(T,Y); with periodic boundary conditions (which is not implemented)
• plot points x=sx(t); and y=sy(t); and let t go from T[0] to T[n-1].

As a workaround to periodic boundary condition we can let the spline go through the closed curve a few times. It's a bit of a hack but it works well.