**Engineering drawing and projection definition :**

Geometric projection is the obtaining of the plane geometric shape resulting from the intersection of projection rays passing through the points of the edges of the body with the projection plane to create a clear picture of the body with its different positions in the space. The projection plane is located behind the body or in front of the body.

**Depending on the location of the C projection source, the projection is classified into two basic types:**

**1) Central projection.**

2) Parallel projection

**Central projection**

**In this type of projection, the center of the projection rays is a specific point in the sphere, from which all the projection lines that give their intersections with the plane of the projection as it passes through the edges of the body are projected to project the object into the plane.**

Central projection gives complex fees, and is rarely used in industrial engineering drawings.

**Parallel projection**

**In this type of projection, the location of the projection beam source is an imposed point at infinity, where the central projection lines become parallel lines between them.**

Parallel projection is classified according to the angle of inclination of the projection lines at the projection plane into two basic types:

Inclined projection: in which the projection lines are oblique at the projection plane.

Vertical projection: in which projection lines are perpendicular to the projection plane.

The object is positioned so that its main surfaces are parallel to the projection plane, and the projection lines are perpendicular to the projection plane and thus the resulting shape on the projection plane is known as the vertical projection. In this projection, we find that each letter of the body is perpendicular to the plane, its points applied to each other in the projection, and that each letter parallel to the plane is the same shape and length in the projection.

**Inclined Projection :**

Oblique projection is a
parallel projection in which the lines of sight are not perpendicular to the projection plane.

Commonly used oblique projections orient the projection plane to be
perpendicular to a coordinate axis, while moving the lines of sight to
intersect two additional sides of the object.

The result is that the
projection preserves the lengths and angles for
object faces parallel to the plane.

Oblique projections can
be useful for objects with curves if those faces are oriented parallel to the
projection plane.

To derive an oblique projection, consider the point (*x*0, *y*0, *Z*0) projected to the position (*xp,yp*) .

The projectors are defined by the two angles: Î¸ and Ï•, Î¸ is the angle between the line *L* =[(*x*0, *y*0), (*xp, yp*)] and the projection plane, Ï• is the angle between the line *L* and the *x* axis.

**What is oblique
projection in computer graphics?**

Oblique projection is a simple type of technical drawing of graphical projection used for producing two-dimensional images of three-dimensional objects.

Oblique projection is commonly used in technical drawing.

The cavalier projection was used by French military artists in the 18th century to depict fortifications.

**Vertical projection**

The space projection levels are divided into four sections (four angles) the object to be projected is placed so that the main faces are parallel to the projection levels.

The projected body projection in the horizontal plane is called a horizontal projection, and the projected plane in the vertical plane is projected as a projection, and since the projection of the body projections takes place at one drawing level (drawing board), therefore, the projection levels should be unified in one level after the projection of the object on each of them, by stabilizing the plane Vertically and rotating the horizontal plane around the ground line at 90o angles to apply to the vertical plane (Fig. 2-3) Thus the projection levels are combined into one drawing plane.

**Projection of engineering objects**

**The basic elements of the engineering body**

**Objects (mechanical parts) consist of basic geometric figures (parallel rectangles, pyramid, cylinder, cone, grouped together with geometric positions with respect to their functional performance later on.**

**Why We**

**need to**

**study drawing ?**

**Why we need to study engineering drawing and projection in computer engineering ?**

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