topic Re: Fit a spline to a closed form (in this case an airfoil countour) in Discussions

Fit a spline to a closed form (in this case an airfoil contour)

shampton82 — Thu, 10 Apr 2025 03:20:36 GMT

Hey everyone,

Is there a way to fit a spline to a shape in graph builder (or any other platform?) I am trying to fit a spline to a set of X/Y data points that fall on the outside of an airfoil contour.

So here is the data

this is what the smoother function currently gives

and this is what I would want (the blue fitted line)

If I turn on the contour plot and have a value to put into color then the boundary line of the contour plot gets pretty close but it appears to be a linear fit between each point, which works pretty well when there is good hit density, not so much for lower hit densities. Also, it is very sensitive to the alpha value so is taking a lot of tweaking for each vane.

This can currently be done in Solidworks (a CAD program) but it is SO slow to do it with how you have to bring in the data.

I'm thinking this would have to be a wish list item but not sure if someone could come up with something creative!

Thanks for any ideas!

Steve

Re: Fit a spline to a closed form (in this case an airfoil countour)

Craige_Hales — Thu, 10 Apr 2025 03:00:23 GMT

Not sure if there is a platform, but you can do it in JSL. Make a table of the x and y values, and a t value that might be the row number, or maybe just a linear 0...1 over the range of the data. Then use SplineEval with x,t to generate a bunch of smoothed x and repeat with y,t to make the smoothed y values.

https://community.jmp.com/t5/Discussions/Bezier-interpolation/m-p/257852#M50666

A 2D spline is a parametric curve using t as the parameter and a pair of formulas (spline eval) that produce the interpolated answer for between values of t.

JMP also has a path() function for graphic scripts that has an SVG-like bezier command.

Splines don't go through the points. Bezier path does go through the non-control points. I suspect you want a spline.

Re: Fit a spline to a closed form (in this case an airfoil countour)

shampton82 — Thu, 10 Apr 2025 03:30:53 GMT

@Craige_Hales

You ROCK! This link

https://community.jmp.com/t5/Discussions/Bezier-interpolation/m-p/257852#M50666

had this buried in it and it works great! I'm still going to try and learn the JSL way as well but this gets me what I need in the short term. Thanks again!!

Steve