Help: Offsetting Panels on a Sphere (geodome)

Replies to This Discussion

Permalink Reply by Luca Anna on January 26, 2014 at 11:26am

grasshopper file

Attachments:

• Geodesic Offset Help File.gh, 13 KB

Permalink Reply by Luca Anna on January 26, 2014 at 11:27am

Hopefully the solution will help solve my loft error, I' want to achieve this attached extrusion all over the sphere eventually!

Attachments:

• 1.PNG, 106 KB

Permalink Reply by martyn hogg on January 26, 2014 at 12:31pm

It's possibly something to do with the directions of the curves output by the Geometry Gym component. Perhaps the directions of those curves change from one half of the dome to the other. You could check this in Rhino - Analyze >> Direction.

I don't know if there's any way to align curve directions, you might be able to break the curves down into points and then re-create aligned, clockwise polylines so that the offsets are all the same direction.

Have you tried asking the Geometry Gym guys?

Permalink Reply by Luca Anna on January 26, 2014 at 12:39pm

That's a great call, I've just emailed them. In the meantime I'll have a go at your suggestion. Thanks for the input.

Permalink Reply by martyn hogg on January 26, 2014 at 1:39pm

The other way to look at this is to scale the curves about their centres and then move them along a vector between the centre of the dome and the centre of the triangles. Then loft.

I think the Area component gives you the centre of the triangle, so you should be able to get the move vectors

Permalink Reply by Daniel Piker on January 26, 2014 at 1:58pm

Weaverbird is also great for this sort of thing:

Attachments:

• geodesic_offset.gh, 10 KB

Permalink Reply by Jon Mirtschin on January 26, 2014 at 1:58pm

Hi Luca,

Is this the type of result you want?  I calculated a plane on the centre point of each polyline to control the offset.  It's also better to "join" surfaces to make a brep than calculate a boolean difference (which is much slower).

Hope it helps,

Jon

Attachments:

• GeodesicOffsetHelpFile.gh, 25 KB

Permalink Reply by Luca Anna on January 26, 2014 at 2:15pm

Thanks for all the input everyone, I tried your last suggestion Martyn, which worked and I've attached here if anyones interested.

And I'm just downloading Weaverbird to check it out, so thanks for the tip Daniel.

Thats what i was after, thanks, Jon. I didnt't know there was an alternative to boolean difference, I use boolean difference commands all the time! I've studied your definition and think I've worked out how your doing it differently, I'll try and apply that technique in future.

Attachments:

• Geodesic Offset Help File solved.gh, 7 KB

Permalink Reply by martyn hogg on January 26, 2014 at 2:27pm

While we're all on this subject, does anyone know how to handle this with only the points as inputs, i.e.without the polyline curves that define each panel?

Permalink Reply by Daniel Piker on January 26, 2014 at 2:52pm

Triangulating a set of points when they can't be easily projected onto a surface becomes a lot harder, though there are ways of doing it - sometimes you can use Proximity3d, remove duplicate lines, then apply Weaverbird's 'Mesh From Lines', though this approach will only work when the points are fairly evenly distributed, so you can set the proximity threshold to avoid unwanted edges.

otherwise you could use Dave Reeves' ball-pivot implementation