Improvement Request: Quantify Curvature Comb

matthew_stacy

https://forum.onshape.com/discussion/14195/quantify-curvature-comb-local-magnitude-and-direction-of-curvature#latest

I would like to be able to quantify the magnitude and direction at any point along a curve.  OS currently provides a useful graphic curve comb with a display-minimum-radius option.  It would be really nice to be able to determine the curvature (magnitude and direction of a comb tine) at any point along the curve.

S1mon

I'm curious why you want this info. I can think of a bunch of possible reasons, but curious what yours are.

matthew_stacy

@S1mon, improved aesthetics are one aspect of my interest.  Imagine that you were trying to match the curvature in a particular region of the front quarter panel of a car to a particular region on the rear quarter panel.  It's rather difficult to match entities that you can't measure.

Another application would be motion control.  Imagine if you were designing an axial cam (wrapped around a cylinder) and wanted to identify all portions of the cam profile where the radius of curvature was less than the radius of the cam follower.

Local curvature data would also provide data-points to evaluate the derivative of curvature, corresponding to "jerk" (rate of change of acceleration) for the cam example in the preceding paragraph. @E@Evan_Reese recently published a excellent video discussing curvature that included examples in highway design and motion control (https://www.youtube.com/watch?v=X714INhNYL0&feature=youtu.be).

@S1mon please elaborate on the "bunch of possible reasons" that you referred to in your reply.  How would you utilize local curvature measurements?

S1mon

The curvature plots can show the minimum radius already which should cover your cam follower example. It's also useful for any sort of machining or sheetmetal tooling concerns.

I don't usually care about the absolute value of the curvature except maybe occasionally the minimum radius, but being able to set G2 or G3 constraints anywhere along a curve is essential for good surfacing. Other CAD tools can do this.

To use your example of the front and rear quarter panels, for something where things need to be visually similar, I'm happy to be able to show the curvature plots of multiple curves using the same scale - which Onshape already does. For things like pseudo radii which are fully G3, I would want the peak radius to be essentially the same.

A gaussian curvature plot of surfaces, and curvature plots of the U/V lines would be helpful. The zebra stripes are decent, but we really need more surface evaluation tools.