WISH: Improvement in _Radius

Wish: When calling _Radius, add a Surface option, which prompts to select a surface, then U or V isocurve direction. The display would then show as Radius currently does when analysing the radius of a curve, with the figure displayed at the tooltip, but the isocurve being measured would also highlight and dynamically move across the surface with the cursor and the rad. display.

Perhaps it could get really clever and allow simultaneous selection of U and V directions, with the tooltip showing both radii?

I know that we currently have the colour Curvature Analysis tool, but that is often ‘woolly’ and doesn’t discriminate between U and V.

This seems like a good idea.

In the meantime you could use a macro something like this:

ExtractWireframe pause
setobjectname "tempcrv"
Radius pause pause
-selname "tempcrv"

Matt, I don’t know if the Curvature command helps you here - it currently reports curvatures only of course and not radius… but you can get the radius from that…

3-D Point: (1.91772, 10.0526, 0.353111)
3-D Normal: (-0.952277, 0.247196, -0.17906)
Maximum principal curvature: -6.97703 (-0.26131, -0.963407, 0.0596955)
Minimum principal curvature: -0.341564 (-0.157751, 0.103637, 0.982025)
Gaussian curvature: 2.3831
Mean curvature: -3.6593

But, is what you are after a radius on the iso or a radius of principal curvatures of the surface? They’d be the same or close on nicely arranged surfaces but not so much on twisty ones…


Radius = 1/Curvature
Curvature has the advantage over radius that the curvature of a straight line is 0 and the curvature of a gentle curve is a small number. The radius of a straight line is infinite and the radius of a gentle curve is a large number.

@pascal Perhaps a option could be added to Curvature to show the curvature circles and report the curvature of the iso curves rather than the principal curvatures. Or a report of the curvature of the iso curves could be added to the report from Curvature.

Hi David (and all) - I’m not sure yet what the purpose of getting radius or curvature info about isocurves is.


Hi Pascal

I’ll take a look at Curvature. The radius is what I’m after. When machining handrail profiles (especially internal corners) I have to make sure that the radius at any point doesn’t go below what the cutter I’m using can provide. This minimum radius is dictated by the minimum radial distance from the cutter axis to any given point on the cutter profile. As such, this information isn’t directly yielded by the handrail surface. I hear your cautionary note about minimum surface radius not necessarily lying on either a U or V isocurve, but when using profiled cutters rather than a multi-pass CAM paths with a bullnose cutter, it is normal to have either the U or V match the cutter. If you don’t it gets difficult to validate things.

OK, maybe that answers my question about why the iso matters…

So CurvatureAnalysis > Min radius display will not necessarily give the right info if the surface is skewy… is that correct?


Just checked out Curvature. In terms of user interface, it is very much the kind of thing I had in mind. On the example I was looking at, the dynamic wires fly out of view and are quite difficult to comprehend because the radii in many cases are large. For the reasons stated above, the curvature readout isn’t much use to me. I like the idea of being able to mark points.

I think he would like to have a surface that has both. It would be a surface like fillet that describes a perfect rolling ball and has principal curvature aligned precisely along isocurves.

Hi Matt - this is not for isos, but for the surface radius - see if it helps for now…

SrfRadius.py (729 Bytes)

It marks the location, reports radii and names the marker point with the min and max radii so you have some reference (on Properties for the point) later.

@MattE Ermmm. Got that backwards… file replaced above…


See the attached file which hopefully makes things a bit clearer. It shows two identical (fictitious) cutter profiles. Used to run off straight sections, they will produce identical mouldings. One has a fatter core/shank than the other though, so if they are used to machine an internal corner section, the one on the left will be able to get into a tighter corner than the one on the right.

Because the radii on the cutter profile itself is way tighter than anything I could hope to machine as an internal corner section, minimum curvature analysis will always have its focus stolen by the profile; it cannot discriminate between curvature produced by the cutter profile (let’s call that V direction, for the sake of argument) and curvature produced by advancing the machine head (U direction).Cutter profiles.3dm (75.5 KB)

The router is 5 axis and very often the shapes required are quite free-form, so can become quite difficult to analyse.