Imagine a sphere on which a shape has been drawn. Let's say it is a circle. Now, project that back to the center of the sphere, and you have a cone (of sorts: the base is on the surface of the sphere, and thus is not flat). If the original shape was a square, then the projected shape is a cube of sorts, one face of which has become a single point at the center of the sphere. Is there a simple way to specify the 2D shape and then create the 3D object? I do not actually want the object: I intend to use the object to cut out that cross section from a ring (torus). The whole point is that the edges of the cutout all point in to the center of the ring/sphere. Thanks! Jon

On 2017-05-29 17:01, jon wrote: > Imagine a sphere on which a shape has been drawn. Let's say it is a > circle. Now, project that back to the center of the sphere, and you > have a cone (of sorts: the base is on the surface of the sphere, and > thus is not flat). > > If the original shape was a square, then the projected shape is a cube > of sorts, one face of which has become a single point at the center of > the sphere. > > Is there a simple way to specify the 2D shape and then create the 3D > object? > > I do not actually want the object: I intend to use the object to cut > out that cross section from a ring (torus). The whole point is that > the edges of the cutout all point in to the center of the ring/sphere. If all you want is to cut the torus all the way out, just subtract a tall enough pyramid with square base (polyhedron) or cone (cylinder with r2=0) from the torus. Place the apex of the pyramid/cone at the center of the torus. Carsten Arnholm

jon, polar coordinates are the natural way to specify a 2D shape on the surface of a sphere. Then you can project the shape on a plane to get a shape to be linear_extruded (with scale=0) in a cone.