So far we have studied the known Plane Geometry. Then study what is the geometry, which is primarily intended to teach and must be represented in a flat projection on a three-dimensional object that can be derived from its shape, dimensions and elements that constitute it.
Descriptive Geometry is the science that aims to study the extent considered under its three dimensions: line, surface and volume. Descriptive Geometry is for the drawing that the grammar for a language.
PROJECTION: is a graphical representation, by whatever method of representing an object, such as we see it. The points of intersection between the plane and rays projection from the point of observation and go through the different points of view, are the projection of the object.
In any projection involves three elements:
- The point of observation, eye, light source or point of view. From the vantage point of projection rays are emitted, which passes through all the points of the object, penetrating the surface projection (projection of the object).
- The object being observed.
- The surface of projection screen, flat box, etc.
A. TYPES OF PROYCCIÓN.
By varying the point of observation:
By varying the point of observation:
1 .- Conic projection: when the observation point is in the finite (or relatively close to the object projected 
), all projection rays start from the same point observation and form a kind of cone.
), all projection rays start from the same point observation and form a kind of cone. 2 .- Cylindrical Projection: is one in which the viewpoint is at infinity, all projection rays are parallel to each other and the cone obtained in the previous case
becomes a cylinder.
becomes a cylinder.
varying the projection surface:
1 .- Projection
Oblique projection when the rays of an angle either, other than 90 degrees with the plane of projection.
2 .- Orthogonal Projection: projection when the rays are at right angles (90 °) to the projection plane.
3 .- Projected Outlook: Every projection in one view represents a body in three dimensions, with the way ydisposición as we see in space.
B. Projection plane.
planes are undefined, but may be limited by their traces or lines of intersection with each other. The line of intersection of a vertical plane with a horizontal line called Earth.
planes are undefined, but may be limited by their traces or lines of intersection with each other. The line of intersection of a vertical plane with a horizontal line called Earth.
The plans are named with Greek letters a, b, c, etc.
If two planes perpendicular to each cut are called dihedral angle, if there are three perpendicular planes which intersect or coincide at the same point, forming the trihedral angle. If more than three planes which coincide at one point, form the polyhedral angle.
projection planes can be infinite, but there are three major.
- Horizontal Plane: plant also called object or floor plan.
- Plano Vertical: also called standard.
- Plano Side-view or profile, which can be left or right.
land lines or traces of the three planes are the three Cartesian axes X, Y, Z.
land lines or traces of the three planes are the three Cartesian axes X, Y, Z.
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