Full Version: Hemispherical dome design ?

Hi Forum. I'm trying to design a hemispherical dome that is made up of a standard tessallating curved piece. Think monolithic dome as in truly spherical ( not geodesic ) but instead of being a monolithic structure the dome is divided into curved pieces that are identical. Towards that end I started with an icosahedron, thank you to node editor and script creators, which I projected onto a hemipsherical dome solid. This I realized doesn't correctly project so I extended lines from origin to through vertices of faces of icosahedron are visible in attached .3dm. First question is a simple one...how to create the arcs between three projected lines on sphere surface so that I can boolean subtract the triangle formed from the sphere. I'm unable to find the points where lines intersect sphere surface. More complicated questions below:

-is there a way for me to easily change the basic shape from a triangle to something else, for example, hexagons ? The only reason I started with icosahedron and projection onto a sphere is that I've seen it used by others when drawing geodesic domes. It seems to solve the scaling problem when you are trying to uniformely divide a spherical surface into idehntical pieces, but perhaps with some math in advance a certain shape could instead be arrayed onto a surface ?

-if not such that the only way to divide a spehere ( or dome in this case ) into tessallated hexagons is to use some form of projection, how much could I use the node editor to automate the process ? Not looking for the script, just to know how much of it is possible.

Thank you, Sven

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Attachments:
dome projection.3dm

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Hi Sven,

re:
> I'm unable to find the points where lines intersect sphere surface.

Are these the lines here? :



If so, select the lines and the sphere:



And run Construct > Curve > Isect . That command will generate curves at intersections between surfaces or points at intersections between curves and surfaces:


- Michael

Image Attachments:
sven_sphere1.jpg  sven_sphere2.jpg  sven_sphere3.jpg 

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Hi Michael, thanks for answering. I should have remembered Isect, a little rusty after sometime away from drawing. Feel like I should be able to create an arc between points (created by Isect) and the surface of sphere (either inside or outside), but unable perhaps because points aren't really on surface. This could be because of some inconsistency in my drawing. Curious if I should be able to create an arc on surface ? So instead I created a closed curve between said points and "project"ed onto sphere surface after changing cplane to the origin.

Thanks for patience, Sven

Attachments:
dome projection.3dm

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Hi Sven,

re:
> Curious if I should be able to create an arc on surface ?

Using which command, do you mean with Draw curve > Arc > Center?

The arc center point draw command is focused on drawing an arc on a plane. If you pick the arc center point on a surface it will use a drawing plane with the plane origin on that point and a z axis along the surface normal.

So the arc will be on a plane something like this:





That tool does not know how to draw the entire arc on a surface because that is only possible in special cases.

But I think arc through 3 points will do it if you put the 3 points all on the sphere surface.

- Michael

Image Attachments:
sven_sphere4.jpg  sven_sphere5.jpg 

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Thanks for center arc explanation because it now makes sense based on what was happening. With the addition of 3rd "on" point on the surface the 3 pts arc works.

Sven

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