Perspective Question: Can Object have different Vanishing Point LENGTH?
4mo
P J
First and for all, sorry for the rough sketch and grammar. I would like to ask is that even possible for an object to have different vanishing point length? I find this problem when i start drawing object with different vanishing point length. Question is do i need to maintain the same vanishing point length or not? There are two example there. Example 1: I find the first object vanishing point and the length of it. I copy the first length and drag it to different vanishing point for my second object. Example 2: I find the first object vanishing point and the length of it. However, I draw different vanishing point and different length for it. May i know which one is correct? Or none of it is correct. If so please guide me or teach me. I really want to learn and know it. Many thanks in advance :)
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Gabi H
I’d like to edit my response. A few people pointed out the flaws in what I’d said and I see that I was wrong. The vanishing points would be different distances apart when objects rotate or change orientation. It’s easy to see this when you use a Station Point to find the vanishing points. I hope I haven’t caused too much confusion.
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Mark Sukaiti
This may help you: Think of an infinite gridded plane, all vertical lines converge to the same VP no matter how large the plane is right? Infact no matter how big the plane is each square on that grid talks about each box that can be extruded from it where each individual box face the same direction and are aligned with this grid. (see first attached pic) Now imagine this infinite gridded plane turning in space, this would mean each box on that grid turns as well right? but then this means from a 1 point perspective where the second VP is off at infinity is now somewhere on the horizon line which would mean the distance between the VP has changed right? This is the keypoint though: Each box now on that grid share the same distance of VP. (see second pic) So essentially here are the keypoints: 1) If the boxes face the same direction they share the same VP and therefore share the same VP length. 2) If the boxes arent facing the same direction they wont share the same VP length. 3) This means VP is kind of fixed in space before drawing the box, where each individual angle of the box has their own unique set of VP somewhere on the horizon line. When it comes to focal length it basically means the distance between these infinite number of fixed VP change.
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Vincentius Sesarius
The simple answer is none of them is correct. But, here's the thing that get people confused, even though it's not correct, but you can still use the 'different vanishing points' technique in some limited cases. I guess a lot of people get confused with vanishing points. Vanishing points exist first, thus they affect the objects in the scene, but it's not the other way around. The position of the vanishing points cannot change just because the objects in the scene move or rotate. Even though there's no object in the scene, vanishing points will still exist. You see, the reason vanishing points themselves exist in the first place is because there's a camera shooting the scene, if there's no camera then there's no vanishing points. Thus the only thing that can change the position of vanishing points are when you move or rotate the camera (changing the camera position or angle), while the 'distance' between vanishing points can change when camera lens' focal length also change (you may have heard the term 50mm or 200mm in camera lens, that's the focal length). So in reality, there cannot be two different sets of vanishing points in one scene, leave alone different 'distance' between the vanishing points. There can only be one set of vanishing points and one distance in each scene, no matter how many objects you have in that scene. As many have pointed out below, the confusion starts when we can actually try to change the position of vanishing points, while maintaining the same 'distance', to portray objects rotation relative to the camera. There are some cases where you can successfully and correctly do that, but in some other cases it doesn't work. I've attached some 3D reference I made in Blender to show that, in that particular scene and camera angle, when the object rotation is counter clockwise, it does work, but when the rotation is clockwise, it just doesn't work.
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P J
4mo
Really sorry for the late reply. Recently i m busying about my assignment. I just saw this and really appreciate the 3D render and explanations. From your explanation and the comments below, i understand that there cannot be two different camera lens (focal length). Which really help me so much. Once again, thank you so much. :D
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Răzvan C. Rădulescu (razcore-rad)
The lengths don't stay the same and it's really easy to picture this. If you rotate the box enough, it will become 1 point perspective. 1 point perspective means that "the other vanishing point" is at an infinite distance. So the more the sides get parallel to the horizon, the larger the distance between P1 & P2. This is one of the difficulties with learning perspective. There's two ways to do it: 1. Calculate everything. 2. Practice and build intuition. I personally go with 2. especially since we have access to free 3D software. I'd suggest you fire up Blender or something and play with the camera set-up and focal length. And start with a cube. Good luck!
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john jo ong
if you rotate the box clock wise the vp1 and vp2 should rotate clock wise as well, as long the degree is 90. in real world situation you have to make an educated guess because its not practical to use a protractor every time you draw. if you test it with a 3d software all your problems will be solved.
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Yiming Wu
Yes, of course, that means the object is rotated.
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P J
4mo
Hi Yiming, thank you so much for the explanation. It really help me so much!!!
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Jean-Francois (Jeff) Durix
correct! My answer to the question was also that both are correct depending on what you want to represent. The simple rule is parallel lines meet at the same vanishing point and all vanishing points are on the horizon which is a virtual horizon at the same height as the observers’ eyes
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Jose
4mo
Both are wrong, that's not how perspective works. Boxes with the same orientation will share the same Vps. Remember, parallel lines converge at the same Vanishing point in perspective. If you are trying to rotate a box, then No the length for the VPs do not stay the same for each rotated box. I suggest looking at Scott Robertson "How to Draw" page 25. The two vanishing points for a box should meet at 90 degrees on the Station Point. You rotate that 90 from the station point to rotate a box. The VPs for the rotated box will vary in length due to basic common sense geometry. You'll get it when you see it. hope this helps.
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P J
4mo
Hi Jose, really thank you for your explanation. I think you may little misunderstanding my question and i totally understand your point of view. I am actually creating a scene, objects that have different vanishing point. However, I am confuse that do they need to share the same vanishing point length or not. This is a picture i search in Google that relate what i am doing right now. Thanks to you and Gabi, I do find my answer. Thank you so much.
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Gabi H
I’m pretty sure the distance between vanishing points should always stay the same. There’s a gif on Draw a Box that explains this https://drawabox.com/lesson/1/17/rotation (it’s a rotating box, where you can see the vanishing points moving with the box). I think the distance needs to remain the same or else it would be like using different camera lenses. For example, if you take a picture using a wider lens (the objects look more distorted), take a picture using a long lens and try to put them together, it’s very obvious there not part of the same picture (moderndayjames explains lenses briefly in one of his videos: https://www.youtube.com/watch?v=2XF5YuAK63I , about 4 minutes into the video). I tried to illustrate this using your example number 2, but more extreme. In my example, the green boxes look like they could be in the same scene and the blue boxes look like they could be in a different scene together. But together, the green and blue boxes have very different levels of distortions (because the vanishing points are not the same distance apart) so they don’t work together and make things look weird. Basically the lens stays the same, so the distance between the vanishing points stay the same. Hope this will be of some help! (ps I’m not sure if this is the best way to explain it, or if my explanation is 100% correct, but I’ve heard a lot of people who have much more experience talk about how the distance between vanishing points stays the same in a scene)
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Mark Sukaiti
The distance between VP will change when rotating a box, you misunderstand how lenses work. It helps to understand it this way: If you rotate a box from 2p perspective to 1p persp then the distance between your VP will increase off to infinity, but lenses talks about how much information is captured into the same 2d plane -> More info means more things to cram in which means the VP will squeeze in tighter than usual. VP lengths (and actual VP) stay the same when objects are facing the same direction, your pair of green boxes dont belong in the same scene also because if they are facing the same direction for example so what you are implying there is that one of those green boxes must have been rotated but because you didnt change the length of the VP it doesnt make sense its rotated, therefore its not in the same scene. Either they are aligned with one another and must go to the same VP or if its rotated the VP distance must change (again think of the object sliding into a 1p perspective, one of the VP vanishes to infinity so the distance must go towards infinity) If it helps to understand about why the green boxes dont belong to the same scene think of a infinite gridded plane in 2 point perspective, if those boxes are aligned with each other (that is they face the same direction) then they must go to the same vanishing points.
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Yiming Wu
Dude, no, that GIF is wrong... I just checked and I haven't checked it before. The distance I think he's referring to the distance as circular/angular distance, but remember the projection we are talking about here is linear.
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P J
4mo
Hi Gabi H, really thanks for the explanation. Actually i heard my lecturer mentioned that when you want to have different VP, you must have the same distance apart. I am so confuse why i need to do so. However your explanation really do explain why i need to do so. Really really appreciate your explanation!!! Thank you so much.
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