Flag. Merge the two images by adjusting your eyes correctly to see in 3D (or use VR glasses with phone). Draws straight "sticks" across two non-touching edges of tetrahedron to make paraboloid--set the # sticks to adjust resolution. Fewer sticks makes the geometry clearer. Use X and Y sliders to change orientation.
This stereogram is my hyperbolic paraboloid from July 2022, adapted now for VR (cross eyes to merge the 2 images, if no VR glasses). Merges two images (which have slightly different angles) of hyperbolic paraboloid. Turn with X angle. Draws lines from one edge of tetrahedron to opposing edge at regular increments. The two tetrahedron edges must be those that do not touch. Mathematicians are interested in it for several reasons. It has a "saddle surface" with a "doubly ruled surface" meaning you can line up straight sticks across one edge to another and also line up straight sticks across in the perpendicular direction and they all lie on this surface. As in any ruled surface, a line can be drawn through any point and the entire line stays on the surface. A few famous buildings use this design in their roofs. Such architecture distributes stress evenly and has an elegant appearance.
