C.a.R. > Demos > Non-Euclidean Geometry
The elliptic and the hyperbolic geometries are realized with macros in C.a.R. Here, you see an example in the elliptic (spherical) geometry.
The applet shows the sum of angles in the elliptic (spherical) geometry. The lines are the great circles, and the circles are the normal circles on the sphere. The sphere is projected from the north pole to a plane tangent at the south pole. This is what you see here. the projection preserves angles, and maps circles to circles, but not the midpoint the the midpoint.