Large scale geometry and camera clipping planes

[dasupermunchkin]

Hi,

A scene I'm trying to set up in Maya (3.0) involves a planet and a bunch of spaceships (original . I want to get a real feel for depth and scale when the camera moves through the scene, so I figured I'd try making the planet and ships to scale.

Right now I'm only using stand-in models to see how things would work out, so if you want, you can try this at home, it only takes a minute to set up.

-In the preferences, I set the linear working units to meters.

-For the planet I created a sphere with a radius of 6375000 meters, which is roughly the size of earth. That's quite a big sphere I put the center at (x=-6375000,y=0,z=0).

-For the big ship I created a box of 1500x400x200 meters, and put it at (x=20000,y=0,z=0) so that it's 20000 meters "up" from the surface of the planet.

-I put a standard camera near the edge of the spaceship, in such a way that it'll still see part of the spaceship's surface and then the planet in the background.

-At the center of the planet I placed an ambient light.
-For the "sunlight" I created a directional light with an intensity of 2.
-For the planet I created a Lambert material with a 3D marble for the color, and fit it to the sphere.
-For the ship I created a Phong material with a checker texture with a tri-planar projection so that each square on the checker is 5x5 meters (just so I'd have a reference).

There's the basic setup. Of course, this results in some problems, or I wouldn't be writing this

-When I use auto clipping planes for the camera, some of the geometry (the planet) doesn't show up in the viewport. And when I render, I get a black scene. The Output window says "Automatic near/far clipping values: 0.01, 1.39034e+009".

-When I set the clipping planes manually to near=0.100 and far=6375000, I'll see some lines of the planet in the viewport. When I render, I'll see the ship and the planet, but on the planet here and there faces seem to be missing / not textured or something. It looks weird.

-When I set the far clipping plane to something bigger like 12000000, nothing will show up in the render. Then when I increase the near clipping plane to 1, everything seems to show up fine in the render, but not in the viewport. Only when I bump the near clipping plane up to 2, everything shows up in the viewport. But this means I cant get closer than 1 or 2 meters to any object in the scene, or we'll see a cross section view of that particular object

So it seems that I'm stuck: either

a) I can use a high value for the far clipping plane, but then the near clipping plane has to be a higher value, meaning I cant get very close to the fighters and ships

or

I have to set low near and far clipping planes to be able to get close to the fighters, which means the planet in the background doesn't render correctly.

So - does anybody know of a way to solve this problem? Am I doing something wrong? Does it have to do with unit sizes? Or is it simply a limitation in Maya?

I guess I could always break up the scene in pieces and then composite them afterwards, but that'd be a real pain for several reasons. I'd like to be able to have the planet in the scene so I can playblast animations. I could also maybe make an image plane for the camera somehow, although it'd be tricky I think, considering the planet has to look 3D while the camera covers quite some distance...

Hope you can help me out or point me in the right direction... And if you can point me to a Maya mailing list so I can post this problem there as well, I'd appreciate it

Thanks

Gertjan

[msimon]

Whoa! Hold on a second. Your units and geometry are way too big! Your basically cramming up Maya's memory with numbers that are way too large. You can't build things that large (especially planets!) to scale that way, and expect them to render correctly. That is why you are encountering problems. If you want the planet and the spaceships to have the correct relational scale, then divide your huge numbers by the same number, something like 6375000. This will give your planet a scale of 1, which Maya can deal with.

Mike
www.scimation.com

[dasupermunchkin]

I sort of suspected / understood Maya would not be able to handle such huge numbers. Or rather - such extremes between small and huge numbers.

As for your solution - If i divide everything by 6375000, the fighters (which are only 10-20 meters in length) will become very small.... too small to show any detail probably

As a programmer i'm thinking the problem lies in the "floating point". Basically a computer is able to compute with numbers of a certain number of digits, and where the point is in that number doesn't really matter. So it shouldn't matter if everything is huge or if everything is small. Keyword being "everything". A computer generally won't be able to compute accurately when you're using both huge and small (fractional) numbers, bacuase of the limitation of the total number of digits that a computer can fit into a number. You can imagine that if the max number of digits in a number would be 5, the computer would be able to work with anything from 0.0001 to 99999. It couldnt do 1234.5678 though, becuase that's more than 5 digits, so it'd get rounded off to 1234.6 or something. I'm suspecting this is where the problem lies, but i'm not sure.

Anyway, thanks for your reply. I'm afraid that dividing everything by 6375000 is not going to work though, because of the fighters and the detail etc Feel free to let me know if you think it would work though

Gertjan

[tbriggs]

You are exceeding the precision of numerical representation on your computer by modeling spaceships and planets to true scale. This is particularly the case with camera-z. Your scene is so huge that the difference between the front and back of the spaceship as a fraction of total near-to-far clip distance is too infinitesimal to be represented even in double precisiion floats. Its enough to choke any renderer.
There is no need. A compelling visual representation of your scene could be done with the planets only 100 or 200 times the size of the spaceships. I would turn off the auto clipping plane and just set it to the minimum range that encompasses all your geometry.

/*In theory there is no difference between theory and practice
In practice they are very different*/

[dasupermunchkin]

Thanks I had sort of reasoned along those same lines with the "floating point" thing, expecting Maya uses double precision floats, meaning this causes problems.

So a practical solution would be to use smaller planets. Won't this look "wrong" then though when the camera moves around a lot? Or is that one of the things you can get away with becuase the end result is 2D anyway?

Gertjan

[dan-mcfarland]

I have been told that the far clipping range needs to be within 20 000. Beyond 10 000 it tends to get squirly,and above 20 000 is guaranteed trouble. My experience seems to support this.

Dan

[pgo]

Hi Gertjan

Im new to the whole 3d scene but from the short time i've been around the most important thing ive learnt is that everything you see on film/tv/games etc etc is all achieved by illusion. So as the guys above said, youre best to just drop the scale of your scene and make a 'scale model' if you will. Even now but mainly before CG became prominent, scale models we're used loads in films eg: starwars etc and i believe those shots look a hell of a lot better than their modern CG counterparts (dont want to start anything thats just my opinion!). The trick is to manipulate the camera rather than the scene and you can do anything, you can give your scene an immense sense of scale with camera trickery. So although technically i cant really offer you much advice, just thought i'd throw that principle in because it might save you a lot of work!

Good luck anyway

[dan-mcfarland]

You are correct that alot of it is trickery, but scale is very important. Physiquing, dnynamics, and rendering all require a real scale, centimeters.

Dan

[blk]

thats not true its all based on a visual scale not actually makeing a model 7 inches tall if its 7 inches tall
do you think when they are makeing a character that is 6 ft tall they enter 6 ft into the computer no they just make and scale everything to the size
makeing your objects in Maya real size especially a planet is just asking for trouble

[dasupermunchkin]

Aha, i didn't know that, thanks Is this one of those pieces of knowledge that floats around but is not documented anywhere?

Gertjan

[dasupermunchkin]

Thanks for your comments It confirms what i'd already learned sorta, about the illusion etc.

It's just that i have small fighters (10-20 meters maybe) and then a planet in the background, and i want to make animatics with 'm. Which means that if i'd have to revert to compositing, it'd be a pain to make an animatic i think, unless somebody can come up with a workable way to do it.

Anyway, the problem doesnt seem to be the size, but the -difference- in sizes of the objects.

Thanks

Gertjan

[dasupermunchkin]

You're right, but i think what Dan is referring to is that Maya works in centimeters internally when calculating Dynamic solutions etc.

You can see this when you set up a simple particle emitter for example. Create a 10x10 cube , then put an emitter next to it, and play the animation. The particles will flow pretty fast. When you set your units to meters and play it again, the particles should flow a lot slower becuase the speed you set for the particles seems to always be in centimeters, no matter what unit size you set in Maya. And this goes for many more things in Maya apparently.

Gertjan

[dan-mcfarland]

The intrnal measurment of Maya is in centameters. Renderman aso ecpcts measurments in centimeters and Radians. The scale doesent have to be a 1to 1 ratio either.

[growler]

Most Engineers and Builders maintain that Centimetres are for Dressmakers.

Anyway, Compositing is probably your best option, but play with you camera lens first- you might be able to fake it with a short (wide-angle) lens.

just my 2c

G
S

[anim8z]

Speaking of real world scale, SPI originally tried out Stuart Little at the scale he was supposed to be, but things (particularly the cloth) looked unnatural so he ended up being about 3 feet tall for the animators (at least that's how I remember it from the LA Siggraph).

I'd hate to see what would happen if the guy who built the planet to real-world scale tried to animate something microscopic.
Jon