投影被定义为将三维点映射到二维平面。投影有平行和透视两种。
1. 平行投影：
建筑师和工程师使用平行投影来创建对象的工作图，因为完整的表示需要使用不同平面的对象的两个或多个视图。
平行投影用于显示图片的真实形状和大小。当投影仪垂直于视平面时，称为正交投影。平行投影是通过从物体上的每个顶点延伸平行线直到它们与屏幕平面相交而形成的。交点是顶点的投影。
2. 透视投影：
艺术家使用透视投影来绘制三维场景。
在透视投影中，投影线不保持平行。这些线会聚在一个称为投影中心的点上。屏幕上的投影图像是通过会聚线与屏幕平面的交点获得的。屏幕上的图像被视为观看者的眼睛位于投影的中心，投影线将对应于来自物体的光束的路径传播。
透视的两个主要特征是消失点和透视缩短。由于透视缩短，物体和长度从投影中心看起来更小。离投影中心的距离越远，出现的物体就越小。
平行投影和透视投影的区别：
| SR.NO | Parallel Projection | Perspective Projection |
|---|---|---|
| 1 | Parallel projection represents the object in a different way like telescope. | Perspective projection represents the object in three dimensional way. |
| 2 | In parallel projection, these effects are not created. | In perspective projection, objects that are far away appear smaller, and objects that are near appear bigger. |
| 3 | The distance of the object from the center of projection is infinite. | The distance of the object from the center of projection is finite. |
| 4 | Parallel projection can give the accurate view of object. | Perspective projection cannot give the accurate view of object. |
| 5 | The lines of parallel projection are parallel. | The lines of perspective projection are not parallel. |
| 6 | Projector in parallel projection is parallel. | Projector in perspective projection is not parallel. |
| 7 | Two types of parallel projection : 1.Orthographic, 2.Oblique |
Three types of perspective projection: 1.one point perspective, 2.Two point perspective, 3. Three point perspective, |
| 8 | It does not form realistic view of object. | It forms a realistic view of object. |