The image of an object cast onto a plane is called that object’s projection.
All the experiments done on how shadows form have shown that light rays travel in straight lines through space.
In the topic of projection as well, the shapes of the projection rays are also taken to be straight. This way, the spatial lines that are assumed to pass through every corner and point of shapes in space, producing the projections, are called projection rays.
Projection rays are generally shown in drawings as continuous thin lines.
For a projection to occur, there must be a viewpoint, rays, an object, and a plane.
Projection Methods
The method assumed to be used to obtain the projection of any shape in space onto a plane is called the projection method.
Assuming that the projection rays travel perpendicular to the projection plane, at an angle to it, or converge conically from a single center point gives rise to the following types, or methods, of projection.
- Central Projection Method (Conical Projection Method)
- Orthographic (Perpendicular) Projection Method
- Oblique Projection Method
Central Projection (Conical Projection) Method
The projection method covering the rules for obtaining the projections of spatial shapes relative to a point called the center is called the central projection method.
In some sources it’s also called the conical projection method.
In the central projection method, the size of the image changes depending on the distance of the object and the viewpoint from the projection plane.
Rays emanating from a point pass through the outline and edges of the object, enlarging on the plane to form the image. Since this projection doesn’t convey the object’s true size and shape, it isn’t used in working drawings; instead, it’s used more for posters, decoration, and architectural drawings.
Oblique Projection Method
In this method, rays that are parallel to each other strike the projection plane at an angle.
Even though one face of the object is parallel to the plane, since the rays strike the plane at an angle other than 90°, they produce different views depending on the angle they make with the projection plane.
Orthographic (Perpendicular) Projection Method
In this method, the projection rays are parallel to each other and perpendicular to the projection plane. Since the rays are parallel to each other and strike the plane perpendicularly, as long as the object’s orientation doesn’t change, no matter how much the distance to the plane changes, no change occurs in the projection. For this reason, the projection on the plane has exactly the same shape and size as the object’s front face.
In technical drawing, all drawings called views are drawn using the orthographic projection method. The oblique projection method, on the other hand, is only applied in oblique perspective drawings.
The projection obtained by orthographic projection is a single-surface image of the object.
The projection obtained by oblique projection, on the other hand, shows multiple surfaces of the object at once, since it’s a perspective view of the object.
International Projection Standards
In Turkey and European countries, the ISO-E projection method is used. However, within the technological relationships between countries, it’s also necessary to know the ISO-A projection method.
ISO-E (ISO Europe)
Used by Europe and the countries we’re aligned with. To draw the object’s side view, it’s viewed from the left.
ISO-A (ISO America)
Used by the United States and the countries aligned with Britain.
For the object’s side view, it’s viewed from the right. This is the answer to a question I’ve come across in some technical drawings online: why is the side view on the left? In other words, it’s because some countries use different standards.
Confused by this part? Don’t worry. We’ll go into more detailed explanations in the projection planes and getting-views sections. You can reach them from the related articles below.
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