Bird's eye view
As a bird's eye view (also "top view" or bird's eye view ) is called in the descriptive geometry perspectives that show an object from above or diagonally above. The viewer sees the object like a bird flying high above him.
In contrast to this, the normal perspective refers to viewing from normal eye level of a standing observer, and the frog's perspective refers to viewing from an eye point below normal eye level. However, all three types do not actually designate the position and orientation of objects in relation to the viewer, but rather the respective position of the horizon line (eye level of the viewer) in comparison to the center of the image.
Bird's eye view as a central projection
Bird's eye views, which correspond to the images made by the human eye and by the camera, are central projections .
Geometric construction from floor plan and elevation
The position of the eye point O and the image plane B is drawn in elevation. A preferred object point is projected from O onto the image plane B and a horizontal straight line B'1 is drawn through its image point. The floor plan must now be positioned at the correct distance to this horizontal. The outline of the eye point O 'is also drawn with the corresponding horizontal distance, its position in the horizontal direction (parallel to B'1) being selectable. For each object point Pi, the image on B is generated in elevation and the floor plan parallel B'i of the image point is drawn. The intersection of the floor plan projection from O 'with this floor plan parallel gives the image P'i of the point in the bird's eye view. The perspective is determined by the eye level and the tilting of the image plane B in the elevation, the horizontal displacement of the eye point in the plan and the distance of the eye point from the object.
Depending on the choice of parameters, the perspective image can draw over the floor plan. With tilt angles other than 45 ° for the image plane B, the construction process is more complicated.
Bird's eye view as an oblique parallel projection
The term bird's eye view also describes an oblique parallel projection (see axonometry ). This is not a central projection and is mainly used in technical and military drawings, and rarely in cartography (see Bollmann-Bildkarten-Verlag ). This projection distorts the object, but at the same time allows the representation of its oblique view as well as a geometrically undistorted floor plan that cannot be seen by the eye or a camera. With this distorting perspective there is also no horizon line.
Bird's eye view in art
Bird's eye view plans, which mostly show a city, landscape or sight from a bird's eye view in great detail, were created in the early 15th century. They do not necessarily use geometrically well-defined projections.
In the 19th century in particular, drawing from a bird's eye view was an art in which artists such as Carl Grote had specialized.