Hi,
I am afraid this is an issue with the TRI algorithm when
points happen to fall on straight lines in some direction
of the surface.
This can be shown if one moves the Z-values a bit
Z[itt] = TMath::Power(10,i);
// shake it a bit
Z[itt] += 0.001 * (gRandom->Rndm() - .5);
After this for me the TRI plot looks ok
Cheers
Otto