Area Moments on mutilple, disconnected shapes

With multiple shapes, is there a way to calculate the total area moments, and centroid for the group?

Rhino3D can do this by selecting all the areas in question, analyze, area moments, however, there doesn't seem to be a way to do similar in GH. Even Brep join returns the individual element's centroids, not that of the group.

Tried union, group, etc.

Any slick way?

Replies to This Discussion

Permalink Reply by David Rutten on September 10, 2012 at 4:37pm

VB or C# scripting. There is no component for computing these properties for disjoint shapes and moments/centroids cannot be simply added together. See the attached about how to leverage the Rhino SDK to achieve this.

David Rutten

david@mcneel.com

Poprad, Slovakia

Attachments:

MultipleVolumeProperties.gh, 2 KB

Permalink Reply by Michael Roberts on September 10, 2012 at 10:31pm

Pretty cool. It works for 3D solids, which is great, but not for planar surfaces, however, to use this for 2D surfaces only, an equal extrusion to the 2D surface, giving it volume seems to allow it to work for that plan dimension. Great script, need to learn the syntax so I can take it to the next level, for now this will do the trick!

Thanks

Permalink Reply by David Rutten on September 11, 2012 at 2:28am

Planar surfaces don't have volumes, they have areas.

Instead of VolumeMassProperties, you need to use AreaMassProperties in those cases.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Andrew Heumann on September 11, 2012 at 9:52am

However, AreaMassProperties seems to lack the "Sum" method you're relying on in your volume example. Am I missing something?

Permalink Reply by Eric Jolley on September 11, 2012 at 9:38pm

Until something that can use multiple regions to calculate area properties comes along I have resorted to a work around where I connect all the surfaces with a hair-width surface and then Region Union them.

Permalink Reply by Michael Roberts on September 11, 2012 at 11:43pm

That Solution is something I did with a composite deck properties: added a small wedge so the areas "connected". It worked, but for something like a bolt group, or separated shapes, it becomes laborious, however, I suppose a "fit closed line", with thickness for area through the individual centroids would work. Nonetheless, that VB script seems as if it'll work, since it does need volume, but for areas with equal volumes, the same result in the planar view.

Permalink Reply by Michael Roberts on September 11, 2012 at 11:45pm

yeah, what makes the VB script work for volume, even with little thickness, and not for areas, exactly same principal, less dimensions.

Permalink Reply by Eric Jolley on September 11, 2012 at 8:50am

Hi David,

Is there a version of this that will work for Area mass properties?

Thanks,

Eric

Permalink Reply by Andrew Heumann on September 10, 2012 at 4:57pm

If I'm not mistaken, to calculate the area centroid without scripting, you can take the weighted average of the individual centroids, where the weight for each is the area of that region.

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