# Scale a triangle on sphere surface

Hi all,

I have an equilateral triangle with vertices on the surface of an imaginary unit sphere.

I wish to scale the triangle, keeping the vertices on the unit sphere, with one vertex maintaining its position.
So in effect the edges scale and the triangle rotates about an axis that is tangent to the sphere and perpendicular to the angle / opposite side bisector of fixed vertex.

Remotely possible?

thx, Bryan

I’d like to say Yes, but I’m not so sure.

Given how SU represents curves via line segments. . . It would seem that this is very difficult to pull off. What are the chances that the lines segments which belong to the sphere actually coincide with the vertices of the triangle. And even then wouldn’t you need to hit actual endpoints of the lines which SU draws? At least those will fall upon the ‘true’ coordinates of the spheres surface. Otherwise any edges, or faces which are generated by SU will just be straight lines between endpoints. and thus quite ‘un-sphere like’ (if I can toss around one of my more fancy technical terms).

BUT, that’s also just dealing with raw geometry. Maybe if your triangle is coming in as a texture/image, which can then be sized as such, and projected, or UV mapped (via plugins) onto the surface; then perhaps everything goes a little more smoothly according to what your needs are for this.

What have you been doing so far, in terms of modeling your idea?

thx Jim,

I am playing with geodesic domes and the layout/proportions of the triangles. I have been iteratively (slowly) drawing them. Maybe change an isocoles to equilateral or whatever. But now I need to grow one to a size that will determine another. Will be ridiculously slow and tedious.

Perhaps a better visual idea: imagine a triangle base pyramid. one vertex at origin of sphere with attached sides unity. the other 3 sides / vertices on the surface. If I didn’t need one surface vertex anchored, probably not so bad.

I get what you say though. When i select the triangle and then the scale tool, it is already a 3d shape.