tinterp - an alternative to griddata

Linear and quadratic interpolation for scattered data

Description

Provides linear and quadratic interpolation methods for functions defined on scattered 2D datasets.

The quadratic method in tinterp seems to be superior when compared to the cubic method in gridata.

Type "help tinterp" & "help tester"

• MATLAB release: MATLAB 6.5 (R13)
• Other Files: tinterp/tester.m, ; tinterp/tinterp.m

[John D'Errico]

An alternative to griddata - similar in speed when you add in the time for the triangulation.

The advantage of this code is if you already have a triangulation, then this saves the time to regenerate it. It also allows you to use a custom, non-delaunay triangulation - not an option at all for griddata.

A disadvantage of this code is it forces you to do the triangulation to call it. Its an unnecessary step for many people, so I'd probably be tempted to allow the user to not supply the triangulation, so if t is empty it could just call delaunay.

This code offers properties similar to griddata. It will not extrapolate beyond the convex hull of the data, Extrapolation is risky business of course, so thats not necessarily bad.

Good help, examples. The quadratic interpolant is an interesting idea.

[Craig M.]

I make hundreds of 2D interpolations for a given triangulation. This function is exactly what I need. Thx.

[Jo Williams]

 

[carlos lopez]

I would like to have more information of the theory behind this. What it means that it is "quadratic"? Should it be exact for 2nd. degree functions? I tried this
X=[1:10 1:10];Y=[zeros(1,10) ones(1,10)];%Data points
f=100*(X').^2; %data points
tri=delaunay(X,Y);%Triangulation
triplot(tri,X,Y) %to interpret the case
x=linspace(0,11,300);y=repmat(0.5,1,300);
fC=tinterp([X' Y'],tri,f,x,y,'quadratic');
plot(diff(fC));%should be linear if the interpolant is exact for 2nd degree

Apparently from this example the interpolant is C0 (i.e. continuous but not differentiable), but it is a little bit misleading what is meant by "quadratic".

I tried to contact the author before posting, but apparently changed addres. Thank you anyway for his contribution.