2D Interpolation of Scattered Data

I have attached the plot that I'd like to interpolate. The red dots are the points that I have imported in to matlab with their respective x (Pressure) and y (temperature at 6000 Pressure) values. What function would you recommend I use to interpolate this? Please be mindful that some curves increase in value before decreasing. Thank you!

[John D'Errico]

Do you have some parameter at each of the red dots, and now you wish to produce a gridded surface that is effectively z(pressure,temperature)?

Or are you looking to be able to read off a point that intersects one of those curves? So perhaps at a given temperature, you want to know pressure along one of those curves?

[Image Analyst]

Do you have some theoretical formula for these enthalpy curves? I would think so. Make it easy for us to help you by providing us with the coordinates of the red dots, and the theoretical formula.

This may help: http://www.mathworks.com/matlabcentral/fileexchange/?term=tag%3A%22digitize%22

and this:

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Answer 1

[Jim Riggs]

I suggest you try "interp2" using the "cubic" method. (you may want to try the "spline" method also). These should be better than simple linear interpolation.

[John D'Errico]

You cannot use interp2 on scattered data. The red dots are effectively scattered.

[Jim Riggs]

I did not assume that the data was scattered. I see eight curves with red dots at evenly spaced pressure values. If the eight curves represent a third, (unspecified) parameter which is evenly spaced, (from curve 1 to 8), then the temperature data is on a uniform grid of pressure x (unspecified parameter).