Dear experts
I tried TGraph2D::Interpolation() in ROOT v6.24 and v6.32 and got different results. I assume that the older one used linear interpolation, then what is the interpolation method for the new ROOT version?
I have already checked this page, but seems it’s still linear interpolation (barycentric coordinates)? Then what’s the difference of interpolation method between old and new ROOT versions?
I guess you mean TGraph2D::Interpolate() ? as said in the documentation it Finds the z value at the position (x,y) thanks to the Delaunay interpolation. I.e: at a given position (x,y) the z value is given by the plane (triangle) above. Yes the new version is still linear.
The difference you see could be due to the change of Delaunay triangulation package. We are now using CDT, instead of triangles.c, which add some licensing issues. The triangles found could be different with CDT in some cases.
Thank you, and is there a way to do the interpolation more smoothly (like Kriging Interpolation)?
No, the algorithm based on the Delaunay triangles simply takes the z value of the point at the intersection of the vertical line at (x,y) and the triangle above that point. To have a smother interpolation you need more points.