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

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

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

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