Hello, I have started working with IDL one month ago and I have some questions about the subject. I have an irregulary grid of several hundreds / thousands datapoints with xyz-coordinates. Now I like to plot a surface which I tried by using 'triangulate', 'trigrid' and 'surface'. It works but I don't know how to set the values of the axis similar to the values of my datapoints. More IMPORTANT for me is the following question: How can I interpolate a 'special' datapoint by a given x,y-coordinate and the surface of the grid to get the best value for its z-coordinate and with its error. I tried it with 'bilinear', but it doesn't work and I don't know why. Thanks for Answers, Andreas