Wrong result with bilinear interpolation

zonexo

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.