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Guest Sethelic

How To Use Ellipse Templates In Perspective Drawings?

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Guest Sethelic

Hi all :) I have a couple of questions regarding the use of Ellipse templates in Perspective Drawing

 

1. Is it true that ellipse templates are primarily Axonometric-ally measure circles? Since it doesn't take into account foreshortening, we won't be able to use it so freely?

 

2. Is how we use templates by aligning the minor axis to the shorter marks on teh template ?

 

3. Is it true that the minor axis is always aligned with the main/thrust axis , even in perspective? (ie the wheel axis)

 

4. Attached below is an example, say i know that the wheel's shaft is at 40 degrees from me, which degree of ellipse template should i use? so that it is correctly placed like how the shaft is perpendicular to the wheel in plan view

post-10091-1171565118.jpg

 

5. Say, when a square/rectangle recedes into distance it foreshortens. so i'm wondering does the Ellipses

(along the same receding plane) actually Change its TILT when it recedes or does it remain the same but just gets scaled down. I understand in reality its tilt doesn't change, but im referring to whether it changes in Perspective drawing .i.e we must use an ellipse template of a different degree e.g. the front and back wheels of a v long vehicle

post-10091-1171565128.jpg

 

 

6. Anyone came across any digital program/method to calculate the minor:major axis ratio, acting like a digital ellipse guide?

 

Any other instructions/opinions is welcomed too :)

 

Thanks

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Whew thats a lot of questions. I'll do my best to try and clear some of that up.

 

1. Not positive what you mean with this one. Ellipses are conic sections. I can't think of an instance where the foreshortening of your drawing would cause an issue.

 

2. The marks on the template (depending on the brand) indicate the major/minor axis, so the shorter distance of the ellipse thats marked is the minor axis.

 

3. Never heard the term thrust axis...sounds like you've been hanging out with too many engineers. In the case of car drawings, yes, the minor axis is aligned with the axle (which is pointing towards the vanishing point in 2 pt perspective).

 

4. More math...yikes. Theres no correct degree for the ellipse you've shown because you've got nothing drawn around it to indicate where the circle is in perspective.

 

5. Yes they will change their tilt. The minor axis would point towards the left vanishing point (again picture the axle of a car. The front axle in perspective is not pointing in the same direction as the rear axle). You measure the change in tilt by drawing the lines to the vanishing point. You can then use those lines to figure out where your wheel needs to be.

 

6. Don't get so complicated. You should never need to calculate the ratio for anything unless you're in a math class. In design you should learn to freehand all your ellipses. The templates are there so you can clean up your lines later on, or help if you're doing a lot of concentric rings like on a car wheel for example. You'll never need perfect ellipses in a sketch, they just need to be good enough to convey the point you're trying to get across. If you need to perfect them you can do it in Photoshop later on.

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Guest aplecko

hi

 

Try to find some books on "descriptive geometry and perspective" if you need precise elipse.(no mater if this is cg or freehand work)

Only thing is that you'll have to waste some time on figuring out how to construct it.

Other good thing is that you'll find all the answers regarding perspective and geometry.

 

hope this helps

 

 

cya

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Guest Sethelic

Thanks man, some clarifications:

 

 

4. More math...yikes. Theres no correct degree for the ellipse you've shown because you've got nothing drawn around it to indicate where the circle is in perspective.

[\quote]

 

Hmm, say i'm drawing the front left wheel of a car on the ground and the orange line is the shaft(to 40 deg VP) of the front wheels. And since i know the wheel will be perpendicular to the shaft, what degrees should i use this time? (assuming wheel not tilted and is perpendicular to shaft)

 

5. Yes they will change their tilt. The minor axis would point towards the left vanishing point (again picture the axle of a car. The front axle in perspective is not pointing in the same direction as the rear axle). You measure the change in tilt by drawing the lines to the vanishing point. You can then use those lines to figure out where your wheel needs to be.

 

Why would they change their tilt? The back & front wheel shafts are parallel to each other and vanish to the same VP, which means in theory they are tilted the same degrees from the viewer?

 

@aplecko

 

I have some perspective books but the thing is they construct ellipses using the long & tedious square divion method, i'm trying to find the relationship between using ellipse templates instead.

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I'm still not sure how to answer # 4. My suggestion would be to start drawing boxes with ellipses in them and you'll get a better feel for where the degree should be.

 

5: In real life the axles are parallel, but in perpsective, (vs an isometric drawing) the axles with be pointing towards the vanishing point, which means they are NOT at the same angle. Heres some pics stolen from this tutorial to give you an idea what I'm talking about. I would *highly* suggest if you have $60 to buy the Gnomon Workshop Scott Robertson perspective DVD's. He does a great job of going over ellipses in perspective.

 

http://archive.cardesignnews.com/studio/tu...etch/index.html

 

a-1-point.jpg

 

b-2-point.jpg

 

c-ellipses.jpg

 

I wouldn't worry about constructing things too much. Learning the hard construction methods in the beginning helps, because it gives you a better understanding of whats going on. But by practicing a lot just freehand you'll begin to feel how fat your ellipses need to be.

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Guest Sethelic
I'm still not sure how to answer # 4. My suggestion would be to start drawing boxes with ellipses in them and you'll get a better feel for where the degree should be.

 

5: In real life the axles are parallel, but in perpsective, (vs an isometric drawing) the axles with be pointing towards the vanishing point, which means they are NOT at the same angle. Heres some pics stolen from this tutorial to give you an idea what I'm talking about. I would *highly* suggest if you have $60 to buy the Gnomon Workshop Scott Robertson perspective DVD's. He does a great job of going over ellipses in perspective.

 

 

 

I wouldn't worry about constructing things too much. Learning the hard construction methods in the beginning helps, because it gives you a better understanding of whats going on. But by practicing a lot just freehand you'll begin to feel how fat your ellipses need to be.

 

1. Thanks for the info, so do you mean the ellipse are aligned to the wheel axle in 2d plane, rather than wheel axle in 3d world? Thus the different axles though in 3d world are parallel but in 2d Perspective is not due to convergence to VP, so i can't use that as a basis for measuring ellipses?

 

I would agree with your saying of practicing more freehand, so i was hoping i could have a grasp of the relationship between the minor:major axis & wheel axle, to better estimate. Like how do i know which ellipse degree to use and tighten up since all of them can be lined up against wheel axle

 

2. say i use a 40degrees template, how is the 40 degrees ellipse actually constructed? is the degrees calculate based on the minor:major axis ratio

 

3. So is it true that using Ellipse templates can only be used for Axonometric drawing because their wheel axle doesn't converge? Since in perspective the same receding ellipse would change in tilt?

 

4. This was my initial concept, pls tell me why it is wrong. SEE ATTACHMENT

post-10091-1171626777.jpg

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I've heard that when pictures are taken with a small lense/cheap camera. There will be a fish eye effect, thus the major axis converges between the two wheels. For pictures with a large lense, the major axis line do not converge...it is rather more for tall architecture pictures.

 

For product design like cars, you should make the major axis meet just for the purpose cheating and emphasizing effect. When drawing wheels for car, consider the degree, the convergence of major axis and size.

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Guest Sethelic

@kaiza

 

Thanks, but i've been there already before i posted, in the article he doesn't use just a ellipse template, which is the 20,40 degree ratio above, he instead modified to fit in Perspective, but i've watched people just use the Ellipse template itself without accounting for perspective in the way he does. He uses the traditional method of framing a square around the ellipse before drawing it, i'm more interested in the r/ship between ellipse template & perspective circles.

 

@ aplecko

Thanks for the link, but i can't read the isntructions, its in a foreign language? can you explain how it works?

 

@bowlofnoodle

 

hmm.. i'm not sure i understand what you mean, for tight accuracy isn't teh minor axis usually used as reference instead?

 

@all

can you guys also check out the 2nd reply i posted to Cyberdemon. i posted another picture of my concept and would like your comments

 

 

Thanks all for helping me out here :)

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Guest aplecko

...hm lets try to translate(litteral translation from croatian to english)

------------

elipse is set with two conjugated(i dont know if this word is correct) diametars(lines connectiong MN and QP). contruct large and small axis of elipse.

 

a- large semi-axis

b- small semi-axis

------------

 

sorry on bad translation

 

i'll try to explain the procedure:

 

1.first draw circle from S through M and N.

2.draw line perpendicular to MN line

3.you get P1 on intersection point with circle

4.run long line through P1 and P points nad find middle between them.

5.from middle point make semi circle through S so it pierce the P1 P line

6 you got your semi-axis: a) from p1 to lower pierce & :) from p1 to upper pierce

7.run line through s and upper pierce (dashed green line in .ppt file)

8.from here it is clear...just apply your semi-axis and then run curve through A,B,C,D,Q,P,M,N points and voila;)

 

simple:)

 

p.s. MN and PQ are wheel box split lines

 

i.e. like in this ugly sketch

post-9743-1171835461.jpg

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Guest kaiza

sethelic - anyone who _just_ uses ellips templates when drawing in perspective is fudging - that is, making a trade off between accuracy and ease+presentation.

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Yeah, my biggest issue with templates is that since I don't have a full set (only a smaller diameter set of them in 15 degree intervals) a lot of times you end up having to go with an ellipse thats not really the correct degree.

 

I need to pick up a set of those on ebay at some point (probably not anytime soon since I'm relatively broke) along with a good set of markers, after using other brands I really despise these prismacolors.

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Guest Sethelic

@bowlofnoodles

Thanks for the picture. but i was trying to figure out the relationship of the various angles of the objects in 3D, and drawing them on a 2D plane especially those ellipses.

 

@aplecko

hi, that was a very complicated way of constructing an ellipse.. i didn't really u/s : steps 7, 8. how do u determine the length of CD & AB.

 

@kaiza

ohhh.. does that mean using an ellipse template alone will not create an accurate circle in perspective because those examples i've seen seem to require some modification from a perfect ellipse?

 

@Cyberdemon -

even if u get different sizes, how do you determine which degree of exposure template do u decide on?

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