Hello! I am using the griddata function for a polynomial regression. Triangulate, XDTM, XDTM, TrZ Z = Griddata(XDTM, YDTM, ZDTM, Xout = [X], Yout =[Y], /Polynomial_Regression, Power = 1, Search_Ellipse = 50, Triangles = Tr) I want to interpolate only one point (X, Y, Z), using polynomial regression form dataset XYZDTM using a 50 radius.I have no troubles to get a Z elevation, but i would like to get which points has been used to make interpolation. In other words, i would like to get indices of the XDTM, YDTM and ZDTM points used to interpolate the point X, Y, Z in the search ellipse Thank you for your answer Aurelien boulben Xeosimaging