Graphic projection . It is a drawing technique used to represent an object on a surface. The figure is obtained using auxiliary projecting lines that, starting from a point called focus, reflect said object in a plane, as a shadow.
The main elements of the projection are – as the figures show – the projection point of view or focus (V), the point to be projected (A), the projected point (A ‘), the projecting line (VAA’) and the plane on which it is projected, which receives different names such as projection plane, frame plane or image plane.
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- 1 General classification
- 2 Conical or central projection
- 3 Parallel projection
- 4 The dihedral system
- 1 The dimensioned drawing
- 5 Sources
|Central||Various types of perspective with vanishing points|
|Parallel||Orthogonal||Isometric (Three equal angles (120º), equal reduction coefficient).|
|Dimetric (Two equal angles, two different coefficients)|
|Trimetric (Three different angles and coefficients)|
Conical or central projection
When all the projecting lines pass through a point, it is called a central projection or conical projection, this is the case, for example, of the shadow of an object on a surface when it is illuminated by a lamp (point focus).
It is the one adopted in the conical representation system, or simply conical perspective.
A variant of this representation system is the stereographic projection used for the plane representation of the surface of a sphere, and which is obtained by projecting all the points of the sphere from one of them on the tangent plane at the diametrically opposite point, or on a plane parallel to it, drawn by the center of the sphere.
When the projecting parallel lines are like the above object by lighting the light of the sun -, it is discussing parallel projection or cylindrical projection. It is a particular case of central projection, where the focus of the projecting beam would be at infinite distance.
The dihedral system
This is the case of the dihedral system, in which it is also true that the projecting lines are perpendicular (orthogonal) to the projection plane. In this system, unlike the others, a volumetric representation of the object in perspective is not obtained, but its elevation, plan and profile. From these views, a three-dimensional representation of the object can be achieved in the axonometric system, the projecting lines of which can be both orthogonal and oblique, being the gentleman’s perspective.
The dimensioned drawing
The dimensioned drawing is a variant of the dihedral system, which in practice cannot be adequately described with the aforementioned systems. They are widely used in architecture , engineering , topography , etc.