[AndyT]

What I don't get is that each box has it's own vanishing point - farther away as it gets farther away from the eye level!
Why don't all the parallel edges have the same VP?
What if it was one big box?
I stumbled over this here (just in case you don't like my crappy sketch)

[ July 16, 2002: Message edited by: AndyT ]

[ September 09, 2002: Message edited by: AndyT ]

[ceenda]

They DO share the same vanishing point, as does anyobject with a parallel axis to any other object. By "further away", it means the 'displacement', that is, the measured distance to the same vanishing point. What you can't see in that sketch is that you can trace all the lines to the same vanishing point. That's one of the problems with perspective. The vanishing points are usually so far off the actual work area that is hard to work out the correct lines. A stack of identical cubes on top of each other (either above or below the eye level) will have the same vanishing points.

[ July 13, 2002: Message edited by: ceenda ]

[AndyT]

Thanks!
But on that picture there the edges obviously have different VPs


[ September 09, 2002: Message edited by: AndyT ]

[Ian Jones]

Note: Before I start, let me say that you should take my advice in the knowledge that I am not a professional. I am not a perspective master. However to the best of my knowledge I will explain myself and you can use your logic to figure out whether it is right or not. Hopefully someone else will be able to confirm.


That picture is contradictory to every perspective book I had ever read. It is incorrect. Ceenda is right. The boxes have exactly the same vanishing point if there edges are parallel.

The tutorial at Wetcanvas is completely wrong. There are innacuracy's all over this picture.



The only reason I can see that they have for justification is due to 'perspective distortion'. However the way they have done it is purely an artistic decision they have made, outside of the correct perspective rules. Stick with me here, I'll explain the correct method and you should then understand why they are wrong and why they may have taken artistic license to avoid 'Perspective Distortion'

Lets look at some terminology, 'Perspective Distortion'.

What that means is when you keep drawing the boxes to the same vanishing point, eventually if you venture to far out they become distorted. Just imagine for a second that you drew a box several metres off the top of you normal page area, and you drew it to the correct perspective rules, by making the lines converge at the same vanishing points as a similar box would use if it were at the eye level. Obviously it would look extremely distorted. This is still in correct perspective though, but in reality the object would be far beyond the peripheral vision of any human, so you wouldn't draw it. So, at which point do you decide where the edge of peripheral vision is? and where do you stop drawing those objects? This introduces a term called a 'Cone of Vision'.

'Cone of Vision' refers to an angle of 60 degrees in any direction from the center of vision. This 'Cone of Vision' represents what the viewer would be able to see, within the normal viewing limits. This does actually disregard a large amount of peripheral vision, which goes all the way to about 180 degrees. The 'Cone of Vision' is only 60 degrees because in this area your sight is not blurred like in peripheral vision. Do a quick test right now. Look directly at this dot without moving your eyes of anywhere else ---> . <--- Notice that every where else looks blurry. Try reading some text in the paragraph above. I bet you you can't do it. This is why we use 60 degrees, because it represents an area that is in focus. This area is comparable to the reality of human vision, as you have just tested.

So how do you draw boxes where you can see mostly the top or bottom of them? Well you do it like these pictures correctly show you. Ignore that fact that these drawings actually show the box one way then the other way. One goes left one goes right... just ingore that for our purposes.





I know you are getting impatient and want me to answer this question, but bare with me though, there are still a few more things to talk about.

The thing that the author of the Wetcanvas tutorial fails to tell you is that the 'eye level' represents a bit more than just 'the height at which your eyes observe an object'. So we need to clarify a few more concepts... to understand this a bit more.

When you draw a perspective view, you do so under the assumption that the eye level remains a constant. The point where your eye is looking at is on that eye level. This point is called your 'Center of vision'. This point is also a constant. What this means is that when you draw a perspective drawing, you are drawing as if you are a viewer staring at a single point, without looking anywhere else and without moving or walking around a scene. Just like you tested before with the dot! That dot was your 'Center of Vision' !!!!! I can't stress this enough.

Of course we know that in reality a viewers eyes would wander all around a scene searching and looking over forms and details. But, for the purposes of perspective drawing we can only pick a single 'station point' (where a viewer is standing), 'center of vision' and 'eye level'. They are the facts, and unless you have a 3D program which can draw multiple perspective views animating where the camera/viewer is looking.... then your 'Center of vision' must remain constant.

Introducing another term now. 'Central Axis of Vision'. The 'Central Axis of Vision' represents an imaginary line which starts at the viewers eye point and travels directly away from the viewer to the 'Center of Vision'. It would look like a dot on your perspective drawing. This is much like a camera in a 3D program, which has a line to help you point the camera in the right place. That line represents a line of sight, this is what the 'Central Axis of Vision' is. It is like a piece of wire that extends from your eye point directly away from you. Now imagine being another person, and looking at the viewer from side on. You would see them side on, looking at the piece of wire now being a long line of infinite length. Once you know the 'Central Axis of Vision' you can then accurately determine the 'Cone of Vision'. Looking side on again at the viewer and the piece of wire, draw an angle 30 degrees up from it, and 30 degrees down from it. There you go, you now have a 60 degree viewing area which you can extend the lines to infinity. Also imagine looking down on the viewer from above. You would see the top of their head and a piece of wire extending directly away from them. Do exactly as in the side on view and draw in those 30 degree angles to give you 60 degrees of vision. Combining the two concepts, we now know what the viewer can see. We know how far from side to side, and how far up and down the viewer can see.

Ok. So now you know the facts.

getting back to that unanswered question again.

So how do you draw boxes where you can see mostly the top or bottom of them?





You do it like these pictures show correctly. Notice that if you were to project 2 lines vertically from the 2 vanishing points in the top picture, they would match the two points in the bottom picture. Make sure you understand that. Think of it this way... you don't move, neither does the point your looking at. The object moves around in the scene, not you. So don't think in terms of what you are looking at, thnk in terms of placing objects within your field of vision.

There are several extra complexities to understanding perspective. I will not go into them thouroughly here, but I will briefly mention some of the extra problems.

Being pracitcal now, I can see you saying... "great I understand everything so far, but there's still a few things that trouble me". The most common question I think you'll be wanting to know is.

"So what do I do to figure out my 'Cone of Vision' in the perspective view? I can see how it works in theory.. but...."

Well, there is actually a complex way to accurately establish the exact cone of vision. It involves learning a method of perspective drawing called 'Direct projection'. There is an easier way though.

Looking at this picture again...



Remember how I asked you to imagine what a box would look like if it were literally metres off the top of the page and correctly converged to the same vanishing points as a box at eye level? well... That box was distorted. Imagine the lines that would converge to the vanishing points, the angle between them would gradually get more and more acute as the object moved higher and higher up. Just like this picture, ignoring the incorrect points though, it does help explain.



Basically there comes a point where they start to look distorted, use your judgement to stop at a point where you think they start to look silly. Technically they should never create an angle less that 90 degrees. That is the absolute limit before heavy distortion begins. It is like looking directly at the bottom of the box, it would appear almost as a square with a 90 degree angle. You get it? Once you have figured out a point where it starts to look silly or when it gets to 90 degrees and distorted mark it, and draw a circle by putting the point on your 'Center of Vision' and the radius on that point you marked. Draw within that circle and you should never get an angle less than 90 degrees. That is a rough way to establish a 'Cone of Vision'.

That is it! phew.....

There are more variables, like when an object doesn't have a 90 degree angle, or is positioned at a different angle etc... but ingore it.. I don't want to explain it. Besides any object can be drawn within a box!

Hope that helps... it better do!

[ July 13, 2002: Message edited by: Ian Jones ]

[AndyT]

OMG! I didn't see that coming.
This is obviously something all the ambitious ones among us don't want to miss!
Am I supposed to change the subject title or something?
Thank you so much!
I haven't finished reading yet...but I'm reading...carefully...

[ July 13, 2002: Message edited by: AndyT ]

[Ian Jones]

The Wetcanvas tutorial... Well it is wrong in saying that the vanishing points change. The only reason I can see they did it like that is to avoid distortion as I have explained above how this can affect images. Basically they moved the vanishing points further and further out to avoid distortion as those angles got more and more acute. In effect this actually has a curious outcome.

By tweaking the vanishing points progessively like that, it is as if the viewer is actually moving their 'Center of Vision' up or down. Very similar to what a 3D program would do to a scene when it is animated. It was done for artistic license, but it is a horrible thing to put in a beginners tutorial. Now that you know the real rules you are quite welcome to take artistic license if you wish, but it would be better to just use a cone of vision to start with.

Coincidentally there is a book that covers the use of perspective and artistic license. It is Called 'Creative Perspective for Artists and Illustrators - by Ernest W. Watson'. ISBN: 0-486-27337-7. I have it myself, it is good but learn the rules before you break them and get a better book that has the correct traditional perspective methods. Something Like... 'Design Drawing - by Francis D.K. Ching with Steven P. Juroszek'. ISBN: 0-471-28654-0. It is excellent, it isn't a dedicated perspective book so you'll get some extra stuff! It is comprehensive though and dispelled all the perspective myths for me! It was such a revelation.

[Ian Jones]

hehe, just noticed you in here... I have updated. Make sure you press refresh to make sure!

[Blind]

*BUMP*

Great info, Ian. We need more replies like this on the forum!

[Dr. Bang]

FUCK WHOEVER VOTED IAN JONES DOWN TO FOUR STARS.

[Ian Jones]

Thx guys, unfortunately it really needs some visuals to improve it. That's another story though.

Bang, you're meant to be loyal to Lunatique!

[AndyT]

You don't mean the pointless kind, do you?


But honestly...the descriptions drew vivid pictures in my head!

[Ian Jones]

Hehe, nice anim. Looks like you got the idea. Heaven knows what the other stuff is for. Just to look 'techy' I bet.

It occurs to me now, that animation is a pretty powerful tool for teaching perspective... hmmm.

Geuss what, the anim doesn't loop forever! It stops after about 3 or 4 minutes. I went to the can, came back and it had stopped!

[AndyT]

Rotfl
Well the tech stuff is supposed to show how critical the degree of distortion is...

Been staring at the screen for over one hour ... your computer seems to be better than mine

[Ian Jones]

haha, maybe it doesn't stop. It'll be one of those unanswered questions of the universe. Either that or my computer had frozen it.

I can see what the tech stuff does now..