MATLAB: Constructing an Offset-Curve

curveCurve Fitting ToolboxMATLABoffset

Probably this question has already been posted several times, however I was not able to find an answer.

I have a smooth curve given as a set of X and Y data points and I am trying to constrcut an offset curve. Bascially my strategie was to search for the perpendicular direction at each point of the given [X,Y] data set and then follow this direction according to the desired offset. This works well for convex curves. However for concave curves, there will be a setback at certain points.

This is actually a very common problem in CNC programming. Commercial CAD and CAM software packages mostly offer a solution to this problem. Unfortunately I was not able to find a solution in matlab. Maybe I am looking in the wrong place…

I would be glad if someone could share their knowledge.

Thanks in advance! Ben

Best Answer

The subject is not trivial, a nice description can be found in the Patrikalakis et al. ebook, Offset curves and surfaces. They also speak about the particular problems of CNC.

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Thanks, with

[pkt,lct] = findpeaks(ChannelE,Frequency,'Threshold',0.8);

this works quite well. What's the best way to create a fitting curve through the points? With polyfit or lsqcurvefit I was not very successful...

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MATLAB: How do i find the intersection points between a surface and a patch

It is hard to find the intersection of a surface and a plane (in general), as it is explained here by Patrikalakis et al. And it may be harder to obtain a smooth curve.

But if you can do with a number of points on the (branches of the) curve(s), you can:

Find the scalar function d of the distance from the points on the surface to the plane
Compute the contour lines of d of value 0, keeping the output of the function:

C = contour(x, y, d, [0 0]);

In C you can find all the points on the surface which belong to the intersection, see the documentation here: ContourMatrix property

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