I am trying to do interpolation using bilinear interpolation, transfer u,v values from 1 structured grid to another.

I found that for different orientation of the pts, I may get coefficients which are of the order 1e-1 or 100. Those with 1e-1 give good ans but those of order 100 usually results in the wrong interpolated value.

I've check thru and it seems that there's no programming errors. Usually just 1 or 2 pts out of 100 doesn't interpolate well. Is this possible? Or is there anyway I can avoid it from happening?

Thank you.

Yes, it is entirely possible to get poor interpolation for some range of orientation of the mesh. Interpolation in more than one dimension is not as nicely behaved as the one-dimensional case. There is no watertight solution, but you may look at transfinite interpolation.