Elements -Descriptive Geometry

Android project in Java, without external dependencies (Android SDK only).
Languages
English (default), Bulgarian, French, German, Spanish. "Language" button on the main screen; the selection is saved and is independent of the device language.
Modes
Point A – projections A′ and A″
Segment AB – horizontal and frontal spread, true size by rotation
Plane ABC – spreads on the plane
Line DE ∩ plane ABC – intersection point I, check if it is in the triangle, visibility
Plane ABC ∩ plane DEF – intersection, common segment of triangles, visibility
Bodies (the "Bodies" button)
Sphere, right cone and right regular prism (vertical axis), up to two bodies
Contours in both projections, intersection line of both bodies, section with plane ABC (with spreads)
The curves are found numerically on a triangular mesh of the surface (accuracy – linear approximation)
Visibility: ray from point to observer (V: +y, H: +z); invisible is dashed line
Visibility
The observer at V looks from the front (larger y = closer), at H – from above (larger z = closer).