Spherical triangle help

Hi all,
I 've just starting using sketch up and I really am excited about it. In order to learn it, I started modelling something that we could call a historic church. I ’ d like to model a spherical triangle and cannot find the way to do it. Could any one give me some idea? (To make things clearer: spherical triangles are used when you want to cover a rectangular space with a dome. They are very usual in Renaissance and Baroque Architecture. It is a bit hard to explain with words what they look like and how they are used, but a description can be found in any book of Architecture History).
Many thanks in advance!

If you’re referring to a “groin vault”, there was a thread about that here: Creating a groin vault with a raised center

Or if you mean a three sided section of a sphere, you can make a sphere and remove the bits you don’t want.
Here is a simple gif making an equilateral triangle section from a sphere.
Note I have ‘Hidden geometry’ (View/Hidden Geometry) turned on to allow me to cut the sphere.
The three arcs are of equal length but you can choose any segments you want. You can increase the segment count to make them smoother or even use different counts on the two circles.

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Thanks you for your prompt response and your willingness to help me. Your help is greatly appreciated, I think though that the methods so far suggested won’t really work as far as what I want to model is concerned. A better word for spherical triangle is “pendentive” and you can see it here: https://www.google.ca/?gfe_rd=cr&ei=Dwa6VtbaGIWN8QfgsYuYAQ#q=Pendentive
Any ideas? Again, thank you very much in advance!


A pendentive dome can be constructed by using the Follow Me tool to create a circumscribed hemisphere:

Create the intersecting planes using the Push/Push tool:

Clean up the geometry:


Thank you all very much for the help! I 'll try again using what you 've shown me. I 'm sure it 'll get there! Thank you again, I appreciate it!

Following up with my pendentive question: I tried to model the thing as you had shown me in your posts but when I tried to use the intersecting planes to cut the dome I could not. If I clicked on the section of the dome that I 'd like to cut, the whole of the dome would be selected. If I tried to delete sections of the dome, (not cutting it), the result would be bad, and the thing wouldn’t look like a roof.Any ideas why the walls don’t cut the dome?
I 'd also like to ask a couple of more novice questions: 1) Whenever I try to move an entity, it gets stuck on the one that it is attached to, so that when I move the one I want to move, the other one gets deformed. How do you resolve this?
2) I tried to make a gothic window on a curved surface. It was difficult to draw the outline, but when I finally had it, the push/pull command didn’t work. Do you know why? Can you think of a better way to model something like that?
Your responses will be highly appreciated, many thanks in advance!

Hi Box,

This helped me a lot in trying to create spheres, thanks!

After you created the first circle on the ground and you start moving the circle tool up the blue axis the circle seem to flip to face you. At this same time it changes from blue to red. I’m trying to figure out what determines the point that it flips. As I practice using the circle tool to create spheres it always seems to be at a different hight or point that my second circle flips.


Camera angle. If you look down it is blue, as you are closer to the blue axis, look horizontal and it will be either red or green depending on your camera angle.
As your view moves so does the associated inference.

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Thanks Box! After reading your reply and then going back to play around with the circle tool some more it finally makes sense to me.

Been playing with the circle tool a lot more and have a much better idea of what I was seeing thanks to Box.

So I thought I would come back and try to recreate what I was seeing done in the second gif posted by ely862me

Maybe I’m just not seeing all the steps in the second gif posted by ely862me but it looks as if after creating the second circle it gets flipped from laying flat to facing the camera, just before it becomes a sphere without camera angle changing.

So at this point I’m thinking…

  1. I’m not seeing all the steps

  2. There is a quick way to flip the circle after it has been drawn and if that’s the case I want to learn what it is.

Maybe I should have started a new post to ask my questions instead of hijacking this topic, if so sorry about that.

As you can tell I’m very new to Sketchup. :wink:

Due to the big size gif I went trough the steps with undo and redo.
To quickly flip the circle just take the rotate tool and press CTRL once, then rotate the circle 90 degrees.
Also, to create the sphere just preselect one of the circles then click with the follow me tool onto the other.

Hmm, well I have been practicing with the rotate tool and can flip and rotate things pretty good now but I still can’t seem to do a quick flip by pressing the CTRL once. Maybe that’s just a Win shortcut that don’t work on my Mac?

As a side note: I have learned so much in these forums from the gif’s you guys post.


Ctrl is used on Win of course but Mac’s have Command isn’t it. Command is used for copying the surface you will rotate, so instead of rotating the actual surface you will rotate a copy of it.

On my mac I use the ALT/Option key to rotate and move copies of surfaces. Maybe I’m just not understanding what a quick flip is. Was thinking the circle would go from horizontal to vertical with just the click of the key and not by dragging a copy of it with the rotate tool but apparently I do have to drag it into position.

I’ll just keep plugging along. I have learned so many new things from this post already.

Thanks again!

On a Mac, you press alt/option to tell move or rotate to make a copy.