# Problem with the size of the Cone of Vision in relation to the Station Point and the Picture Plane

I'm asking this because I don't understand something while studying perspective.

I am curious about whether, in perspective, the distance of SP (station point) should not be set to the actual distance.

For example, I'm sitting on a chair in front of a desk and am trying to draw the desk in front using one-point perspective.
At this time, the distance between me and the desk is very close. Let's assume it's 20cm.
Then, the distance between myself and the picture plane (PP) between me and the desk will be closer.

In comparison, if the height from my eyes to the soles of my feet touching the ground is about 100 cm or more (i.e. eye level), it will be an absurd structure like the picture I attached.

The distance between SP and PP is so close that the cone of vision will be too narrow, and as a result, the field of vision will only be on the horizon line and cannot include objects below it.

Ultimately, if you want to see the objects below, you will need to widen the cone of vision by making the SP distance farther than it actually is.

So in the end, what is the meaning of everything I learned about the relationship between PP and SP? I feel that it is very unnatural to say that the position of SP is the position of view, i.e. 'the position of I'. This is because the actual position or distance I see does not matter, and ultimately the position of SP will have to be set according to the cone of vision.

So, if I want to draw the space that my eyes can actually see, do I forget about my actual location or where the PP is, and only check how wide the cone of vision needs to be and adjust the SP distance accordingly?

Or is there a reason to consider something else I don't understand?

• You say "...whether, in perspective, the distance of SP (station point) should not be set to the actual distance." What is the "distance of SP" and what is "actual distance"? The Station Point is a point (where the eye is viewing the scene) not a distance. And are you taking the concept of picture plane too literally, as in it has to be where the drawing pad is? Commented Jun 4 at 14:58
• @rebusB The 'distance of sp' I am talking about is the distance from pp. And the 'real distance' I'm talking about refers to the distance between the object and the viewer in real space. As explained in the main text, as a result, the location of pp is limited between the viewer and the desk, and as a result, the distance between sp and pp, which are the viewer's locations, is also inevitably shortened. Commented Jun 4 at 23:48
• @rebusb I think what I am taking literally from the perspective book's explanation is that the position of the SP is the position of the actual viewer (myself). In reality, the position of the SP seems to be determined simply by the size of the cone of vision required. Commented Jun 4 at 23:50
• The SP is the position of the viewer. The field of view determines the cone of vision from the SP which is the tip of the cone. Those can both be literal, when you are drawing what you see in life, or virtual when you are drawing from an imagination. The SP does not determine the size of the cone of vision, only its apex. Commented Jun 5 at 16:30
• @revusb No, the ‘distance between sp and pp’ determines the size of the cone of vision. When sp is far away from pp, the size of the cone of vision increases, and when it gets closer, it gets smaller. As I said in the text, that distance is different from the actual viewer's location. So, in order to set the desired size of the cone of vision, you must arbitrarily set a distance that matches the size of the cone of vision, not the actual viewer's position. That was the part I had doubts about. Commented Jun 6 at 0:53

It seems that you are reversing what drives the size of the cone of vision. That cone is determined by your station point (SP), ie where your eye is and the field of view (FOV) you have chosen for your drawing. The cone of vision is completely arbitrary since the field of view can be anything from very narrow (like in your diagram) or very wide.

The picture plane (PP) is a virtual construct. It is set to contain the FOV while being perpendicular to the line from the station point to the scene you are drawing. That is the line that forms the center of your cone of vision. The PP can exist anywhere on that line and as long as it remains centered and perpendicular to it, the scene it captures will be the same. For convenience we imagine the picture plane as coinciding with the drawing surface but it does not have to be at the same point in space. You could imagine it behind the objects you are drawing, as long as you are projecting from the same SP the objects you are capturing will land at the same points on the drawing.

What it sounds like, when you want to change the SP in order to capture more of the space you are drawing, what you are trying to do is fit more into the cone of vision. Yes, moving the station point back will do that if you keep the same angle for your FOV because now that cone is wider where your subject matter is (the subject is further down the cone to a wider part of it). So would expanding your FOV. That makes the cone of vision wider, bringing the subject matter into frame, but it does so without changing your SP. Think of it as making the PP wider if you are holding its location at the same point relative to the SP.

tl;dr: The cone of vision is determined only by the station point which anchors its tip, the direction of view which sets its direction, and the FOV which determines its width.

• Conceptually I am detaching the picture plane from the drawing surface. If you want to consider them always at the same location, then the width of the drawing/PP sets the FOV which sets the cone of vision. Commented Jun 7 at 16:06
• From what I understand, pp is probably the actual viewer location. Because it reflects the viewer's FOV. and sp is seem to be positions where re-observed with a limited field of view (cone of vision) the plane reflecting the viewer's FOV(pp). Commented Jun 8 at 7:18
• @guss2222 - nope. The picture plane is what you 'capture' the image on. Like a film plane. If you are placing it where your station point (sp) or "eye" is then it would actually disappear (it is on the tip point of a cone). I think you are equating it with what you are seeing but that would be the whole ~210 degree spherical view that your eyes/mind captures, not the smaller part of it you are picturing in the drawing. Commented Jul 27 at 16:33
• Haha... I don't know why I'm so confused. So let's look at an example. I'm sitting 20cm away from my desk. I try to 'capture' and draw the image as it is at the distance I am looking at. So shouldn't pp's location ultimately be where I am? Commented Aug 26 at 12:46

To me it sounds like your confusion comes from the size of the cone of vision. Yes, it is tiny in your diagram, and no, this is not how we as humans experience the world. Mostly because our eyes are constantly in motion, shifting the cone of vision around until the image our brain perceives is much larger.

Try this experiment:

Take the cardboard tube from an empty roll of toilet paper or a similar tube. Hold the tube in front of your eye and look at the table without moving the tube. What you see is a very narrow cone of vision like you drew in your question. This is objectively all you can see at one moment in time.

If you want to see your feet, you have to move the cardboard tube down. In that position you won't be able to see the horizon line at all.

It feels unnatural to us because we move our eyes around all the time. Subjectively we humans perceive a wider cone of vision because of our eye movement.

For a drawing this means that it looks more natural to us if the cone of vision is wider than in your diagram

• Actually our natural cone of vision is much wider than implied by OP but we concentrate on a small part of it. I am looking at my monitor from a foot or so away like the desk above, but my eyes also are seeing out the window to my side and the other half of the room to the other side. Our eyes individually have a field of view of about 120°, the two eyes together see 220°. To see your feet yet have the picture plane and the station point at the same location you could instead look through a much larger tube (big enough to stand in in this case). Commented Jun 7 at 15:16