ProE Spline Equation

It is a cubic polynomial, I think!

See http://communities.ptc.com/videos/1418

Can you provide the data and maybe a screen shot of the ProEng curve?

Mike

After some delay due to being diverted on to another project I am back on this one and having looked at the answers they don't really answer my question. I have been given the dimensions of the control points NOT the knots on the curves. I have shown a typical curve below with the control frame in magenta.

From the control points I have been given I need to be able to calculate any point on the curve. I haven't found how these control points relate to the definition of a cubic spline if it is one. Can anyone help?

Thanks,

Andrew

Thanks for asking but sorry I don't have access to ProE, only Mathcad 15. What I have shown is the data I get given. Even if I had the model I wouldn't be allowed to post it.

Andrew

I was asked to carry out some calculations on a surface in a ProEngineer CAD model. The curve above is swept around an axis to define a surface. I need to calculate the height and gradient of the surface at any given radial distance from the axis. All I have been give are the dimensions in the picture above which I thought should be enough to define the curve exactly.

As PTC are trying to promote the integration of Mathcad with what was ProEngineer, (but for some unfathomable reason is now called CreO) I was hoping someone who knows about the Maths inside ProE would be able to help. If that is you - HELP!

Andrew

Vladimir,

thanks for your suggestion but I don't have a license of ProE. I only have Mathcad v15 and the CAD guy's only way to describe the curve in the model is to send me the control point dimensions that I showed in my diagram. There must be a mathematical equation that describes the ProE Spline curve from these control points. Once I know what it is I can reconstruct the curve in Mathcad without needing a ProE license.

Andrew

Finally figured this one out.

Yes the ProE spline curve is a Bezier curve, so no need for importing/exporting and fitting etc. You can just take the dimensional values of the control points from ProE and use a standard Bezier equation in Mathcad to calculate the curve profile, gradients etc.

The reason I thought it wasn't a Bezier was because I confused the Bezier parametric variable which scans from 0 -1 with the length ratio that ProE uses. I asked the Mechanical engineer to provide me with the co-ordinates of a few data points spaced along the curve to check if the cuve was a Bezier. He gave me the co-ordinates of points at length ratios of 0.1, 0.2, 0.3 etc along the curve and I used these values as the parametric variable to calculate the position of the points. This was my mistake it is of course WRONG.

Now if anyone knows an exact equation for getting from the length ratio of a Bezier Curve to the parametric variable that would be helpful. So far I have been forced to use a stepwise approximation.

Andrew