Shadows basic concepts

The nature of light and shade depends on the position of the object relative to the light source.

and the direction of the rays to the surface

Shadows are shown on orthogonal, axonometric and perspective projections of various building structures, buildings and structures in order to give them greater visibility and relief. Drawings of spatial figures with shadows on them allow us to more definitely judge their relative position in space, the shape of their individual fragments.

The image on the drawings of the shadows corresponding to reality, is a difficult task.

In descriptive geometry, when constructing shadows on projections, graphical methods for determining the boundaries of shadows are studied, i.e. consider only the geometry of the shadows. The physical basis of shadows (the intensity of the light source, the magnitude of the illumination of the object, light highlights, etc.) are not considered.

To simplify the construction of shadows adopted a number of conditional provisions:

1. Illuminated bodies themselves are not sources of light.

2. The limit of propagation of the light beam is the first material point encountered on its path.

3. Exposure to air is not taken into account.

4. When constructing shadows, it is believed that light propagates straight.

Illumination is called a torch if there is a point source of light, which is located at a relatively short distance from the object. In this case, the light rays form a bundle of straight lines.

Illumination is called solar if the light source is at infinity. At the same time, the light rays are parallel to each other.

Own shadow

Drop shadow