# Perspective Theory - View

1. Imagine we have drawn a 1-point perspective cube. If we move this cube to the left or right from the station point, does this mean our cube doesn’t rotate, but it only moves left or right and our eyes will move to the left or right to view it?

2. Now let say we have a 2-point perspective cube. How would we move this left or right from the station point?

3. And how would you rotate the 2-point perspective cube?

I hope you can understand what I’m trying to explain. As I really want to be able to understand perspective.

• I guess your fundamental problem is that you have never checked the elementary 3D geometry behind the proper constuction of 2D perspective images of 3D objects. Rectify if I'm wrong. Practical concepts such as vanishing points, terms 1-,2- and 3-point perspective and how to scale properly more distant details to smaller size can all be explained in a 2D plane; drawing textbooks and tutorials do it thoroughly. But they can look confusing if a person starts his perspective drawing practicing from those practical drawing rules without knowing how the projection of 3D objects to a 2D plane works.
– user82991
Commented Mar 4, 2021 at 10:28
• (continued) Knowing = being able to construct a proper perspective image of a simple 3D object by starting a couple of perpendicular engineering drawing like views of the object and by drawing some lines of sight. Perhaps the most simple possible example: [1]: i.sstatic.net/NJ822.png It's a cube and the perspective is called 1-point because only one vanishing point exists. BTW 1-,2- and 3 point perspectives are meaningful only for objects which have rectangular major outlines.
– user82991
Commented Mar 4, 2021 at 10:47
• @user287001 well said, was going to write this answer but was needed elsewhere. In reality i would go further and say that there are even other projection techniques, see the parallel viewplane stops working very well when the view angle is big ennoug say for 120 degrees fov. So clearly even that projection is limited in scope. At some point you need to forgo using a plane and start using a spherical projection plane. Or cylindrical or something else. Commented Mar 4, 2021 at 15:49

I will use the term camera instead of eyes.

Does this mean our cube doesn’t rotate but it only moves left or right and our eyes will move to the left or right to view it?

1. Yes and no.

Here I have several cubes, but imagine it is just different positions of 1 cube. If all the vanishing points are the same, but I do not rotate the cube, it will look different, (Yes) but that does not mean I need to rotate the camera. The eye movement is independent of where I draw my cubes. (No)

But If I start reframing the cube as it moves, there will possibly be one moment where the cube is so far to the left or right that I will start to see another vanishing point.

Because I now need to rotate the camera to keep it on view*. This will rotate all the reference plane, the vanishing points in respect to the point of view, the camera.

Now let say we have a 2 point perspective cube. How would we move this left or right from the station point? 2. Follow the grid, that is why you have a grid in the first place.

But now you changed the references axis, so you need to define left or right based on the grid or on the view plane.

If you do the first one, you have all the cubes matching the grid, although "right" could be no longer "just right" but become "further away".

But if you simply move it right from the plane of view, the view will look "off" because you simply detach it from the grid.

And how would you rotate the 2 point perspective cube?

1. Take a look at these other posts:

At what point does 1 point perspective become 2 point perspective?

Finding the possible vanishing points in a landscape

I recommend you to use a 3D program, like SketchUp or Blender, and play with them moving the camera and cubes so you understand how the vanishing points interact with each movement or rotation.

*Another way to keep the far cube on the frame is to "travel" the camera, from point 1 to point b, without rotating it, this way you will still have 1 point perspective

In the real world, there is an infinite number of vanishing points. Put your phone on a desk. It has one vanishing point in front of you. Now rotate it a bit. The vanishing point moved. Continue rotating it and now you realize that you are seeing another vanishing point from the sides of it, that you were not aware of before.

Did the other vanishing point vanish? No. It is simply out of sight but still there.

But we are the only conscious of vanishing points because we live in an orthogonal civilization. Your phone has parallel lines, it is not a wobbly mass of goo. Your desk, your monitor... Nut you can skew your monitor, rotate it a bit. The chair has fewer parallel lines, the mouse...

Now stand up, and do not move your desk... But move yourself. If you do not look at your desk it is probably out of your sight. But if you turn you can see now the side of the desk. It did not rotate. You moved and compensate rotating your head.

Perspective is the result of multiple factors. like:

1. If the object has parallel discernable lines.

2. Where is positioned in respect to a reference plane. Let's say a floor.

3. How it is rotated with respect to this reference plane.

4. How far is from the viewer (the camera)

5. How this camera is positioned with respect to this object. Up, down, etc.

6. How is the center of view of this camera is with respect to the object.

7. What is the viewing angle of the camera.