Author Topic: visual distorsions (3d Vs real)  (Read 591 times)

Offline TheBadger

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visual distorsions (3d Vs real)
« on: February 14, 2017, 08:21:31 AM »
Hi,

In architecture a trick called Entasis is used to cause a visual illusion. The use is meant to counteract the way the eye sees a straight line over distance.

My question is when modeling a real world structure where Entasis is used in construction (making a curved line so that the form will appear to have straight lines), I would do this to be true to the real world subject. However it means more complex modeling. So does the visual illusion hold true in 3d rendering and in particular TG?




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Offline René

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Re: visual distorsions (3d Vs real)
« Reply #1 on: February 14, 2017, 08:50:44 AM »
I don't think so, unless you use a fisheye or spherical lens for rendering. Terragen uses geometric perspective for default which has straight lines. The curve you see in reality when you look at a straight line is a consequence of the curvature of the lens(eye and camera.)

Offline Oshyan

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Re: visual distorsions (3d Vs real)
« Reply #2 on: February 14, 2017, 07:24:38 PM »
As far as I know TG actually simulates the effects of a camera (basic effects, at least). So it should hold true for TG renders as well.

- Oshyan

Offline TheBadger

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Re: visual distorsions (3d Vs real)
« Reply #3 on: February 14, 2017, 09:04:40 PM »
As far as I know TG actually simulates the effects of a camera (basic effects, at least). So it should hold true for TG renders as well.

- Oshyan

 of course i did see plenty of times, bowing of a model in the render if I was to close to the subject with the camera. these things can be corrected in post just like a photo. But I really was not sure if I could do the other real world things that artists and builders do to counteract.

It makes sense that the same things apply, but I never trust 3D. I am always afraid I will run into some problem down the line that I cant get around... Not just TG but all 3D.


Does any one happen to know the formula for entasis?

What is the curve to distance ratio? So how much curve added to a line for how much distance, relative to how far from the line the viewer is standing?

I was not able to find a simple calculation or rule to follow, but I know there is one.
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Offline Tangled-Universe

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Re: visual distorsions (3d Vs real)
« Reply #4 on: February 14, 2017, 09:14:47 PM »
TG's lens shader gives optically perfect results.
Real world lenses are imperfect and can have distortions, like barrel distortion, which can make straight lines appear curved.

As far as I know TG's camera always renders straight line straight, however -like with real world lenses- as soon as the camera is not level it will give perspective distortions, but not curved ones like with barrel distortions.
See attached image.
A real world lens, even the best wide-angle ones, will show barrel distortion as soon as the lens is not perfectly level with the horizon.
The render below will have curved lines instead, especially along the vertical axis.

Offline TheBadger

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Re: visual distorsions (3d Vs real)
« Reply #5 on: February 14, 2017, 09:40:47 PM »
Hi,

OK. here is an old render default camera.

71814-0

as you can see there is some arc to some very straight lines. But what is interesting to me is that they bend strange. In the real world greek temples had no straight lines. temples were built with Entasis from the ground up. The thing is, the lines on my model are perfectly straight (wrongly), but they distort wrong too.



I modeled wrong since I did not have this info when I started and am redoing things yet again. but this is what I am supposed to do

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Offline TheBadger

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Re: visual distorsions (3d Vs real)
« Reply #6 on: February 14, 2017, 09:44:32 PM »
oops here are the two images that I meant to post above

71816-0



also this one

71820-2

All temples were built like this. The degree was different, but they all used this trick. Scale maters too. The Parthenon is much larger than my subject.

SO I guess I need to learn the formula to calculate the degree based on scale and distance, and also I need to better understand how to use that in 3d rendering.

By the way, real good to hear from U, T-U!
« Last Edit: February 14, 2017, 09:48:27 PM by TheBadger »
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Offline penboack

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Re: visual distorsions (3d Vs real)
« Reply #7 on: February 15, 2017, 10:06:15 AM »
I don't think that is quite that clear cut.
Have a look at this.
http://www-users.york.ac.uk/~pt2/SV22171.pdf

Also from the definitions that I found Entasis is slight convexity in the body of the column.
A deformer applied to the column could be used to produce the effect.

The arrangement of the columns whereby the spacing is reduced at the top looks more likely to be to do with the forces at work in the roof of the building, which are pushing outwards, than aesthetics.
A deformer applied to the whole model could be used to produce the result shown in the diagrams in your post.
So maybe no need for the Math.

A few years back most of the 3D apps introduced cameras that modelled the artefacts of real lenses, I recall that Lightwave and CINEMA 4D added this feature.

Offline TheBadger

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Re: visual distorsions (3d Vs real)
« Reply #8 on: February 15, 2017, 03:00:52 PM »
Mostly I am modeling as simple as possible. but on the one temple I have done and redone, I  modeled every stone. Its kinda the point for me that it is modeled as an exact recreation. Well every stone that is visible.

I am using many of the parts over and over again on other models with slight changes. so the more I get done... the more I get done ::) lol and never get done...

Well it turns out that my subject is part Archaic and represents the exact time of the change to the classical. So I dont need to do as much as I thought with this, since it does not really follow the rules. But I am also modeling a parthenon too and will need to get the curve right on that one since it is classical defined.

I can just use a latitce to deform the model  but I would really rather model it correctly Since I spent so much time finding images of every surviving original part.  :o

Ok, on aside, another thing that I got wrong early on is that greek temples dont follow the golden mean. They actually use a vitruvian man that predates the one we all know by a very long long time. Hard as F-ck to model a bunch of parts and then try to put them together when you are using the wrong ratios!
https://www.youtube.com/watch?v=MLCW0zKR4xk cool if your board.

After the of the classical period

lol. When I started I really thought is would be so simple. Just basic shapes stacked on one another. Nope, not even close. Watch that youtube -what a big job!
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Offline KlausK

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Re: visual distorsions (3d Vs real)
« Reply #9 on: February 15, 2017, 04:40:40 PM »
???
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Offline TheBadger

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Re: visual distorsions (3d Vs real)
« Reply #10 on: February 15, 2017, 06:38:01 PM »
Haha. Google flagged pbs nova as fake news. Too funny.
Well, I promise content is suitable for all.
Pretty cool episode too. My link is not full hd though.
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