View modes in 3D CAD. Part 2 – Perspective view

In 3D CAD software, projections determine the perception of 3D model’s dimensions and proportions. In the first part of the "View modes in 3D CAD" series, we discussed isometric projection. Its alternative is the perspective projection, which we discuss in this post.To get more news about Gstarsoft Tips & Tricks, you can visit shine news official website.

What is a perspective view?
A perspective view is a projection with the center located at a finite distance from the projection plane. In the perspective view objects are depicted by lines passing along invisible non-parallel rays connecting in the center of the projection remote from the observer. This distinguishes the perspective view from the isometric one, where lines pass along parallel rays.

The perspective projection is used in cases where the three-dimensionality of an object needs to be rendered more realistically than isometric view allows. In perspective view lines that are parallel in nature appear to intersect in the projected image – for example, if railroads are shown in perspective view, they appear to converge to a single point called a vanishing point.

The perspective view is usually divided into one-point, two-point or three-point perspective, depending on the orientation of the projection plane with respect to the axes of the depicted object (see Fig. 1):

one-point – a 3D object is created using non-parallel lines converging at one point on the horizon;
two-point – shows the 3D object from the side, non-parallel lines converge at two points on the horizon;
three-point – it has two vanishing points on the horizon, but in addition to them it uses a third, vertical perspective point; a three-point perspective is closest to real perception.
1. Realism
The objects depicted in perspective projection look about the way we are used to seeing them in reality. This applies equally to rendering the external volume and internal space, the external and internal proportions of the object. Realism makes a perspective view a must in 3D CAD software.

2. Accurate representation of object locations
We can say that this is one of the factors that make the perspective view pretty realistic. Compared to isometric projection, which is great for conveying the simple shapes of a 3D model, but can be misleading as to the location of its individual parts, perspective projection gives a more accurate representation of the location of individual parts.
3 . The constancy of 3D
Unlike isometric view, perspective view clearly demonstrates the three-dimensionality of an object, even when looking at the object parallel to one of its axes (that is, at X=0, Y=0, or Z=0).

For example, if we look at Fig. 3, which shows a section of the facade in perspective view, then even with a strictly frontal view (X=0), we can judge the length of the building and the relative position of its internal elements (furniture, doors, etc.).

But as soon as we switch to isometric projection, the internal detail disappears and we get a flat image (Fig. 4).