Viewing Objects

A 3D object, shown on a flat computer screen, is not always shown in an appropriate way. Compare it with taking a photograph. The photographer has to think about a good position from which to take the photo. Also, he has to point the camera in the right direction. When he takes the photo, the result is projected onto a 2D rectangle on the film in the camera. This is how Geocadabra makes the screen representation of an object. The computer screen corresponds to the film in the camera. There are two standard drawing methods to make the screen representation: 1. Parallel projection. 2. Central projection. Parallel projection The drawing is the shadow of the object when the light rays are mutually parallel. In the picture on the right the projection plane is orthographic to the light rays, but the plane can also be oblique. Central projection The drawing is the shadow of the object when the light rays come from a point, for example, a light bulb. The same result is obtained when you look through a window at an object, and draw lines on the window as if tracing over the edges of the object. In the picture on the right the projection plane is parallel to the front of the house, but the plane can also be oblique.