3ds coords boundaries ?
10 messages in this thread
Hi Gary,
We're currently working on a scale for Studio City 2000 over there on ASHOWCASE
and some serious questions appeared.
Is there a limit in coordinates that 3ds can use ? We had a discussion
about "rounding errors" garbling your mesh when 3ds exeeds a 6-digit
margin (100,000).
Is it true ? Does a margin exist ? If so, at what values ?
Thanx,
Michael
Since 3DS uses single-precision floating point numbers to store
vertex coordinates (to save memory and for speed), there is an
inherent limiting range in the overall scale/accuracy of your scene.
This "range of accuracy" is a ratio of the smallest-to-largest
object in your scene.
Gus Grubba wrote up an explanation for how to compute that limit
last year, and I happen to have that handy. Here tis.
– G
Gary,
Remember to edit out the # from the message header when you're quoting
previous messages. Gets a little confusing when they show up as new messages,
numbered a few thousand back.
Kevin Krell – Computer Support Associates
Gary,
Thanx for the reply, but I'm afraid that helps me as much as white cheese on
mars. <g>
After experimenting for a while I think I have to correct my question :
3DS stops displaying coordinates at a number of 1.000.000.
If you move a small object (1-100 units) out there and ROTATE it you get
serious distortions…
The distortion rate seems to be directly related to the proportion between the
moving-out range and the size of the object. I experienced it only when
rotating an object.
Example 1: Rotating a 10-grid box of size 0.01 at 100 produces 1% distortion.
Example 2: Rotating a 10-grid box of size 1 at 10.000 produces 1% distortion
too.
Example 3: size 100 at 1.000.000
produces up to 10%
Looks like Gus could split his atom if he would be able to spot it <g>.
Suggestions…. comments ?
Thanx
Michael
Odd I've never experienced this (or maybe I just am not undersanding it
properly)
I do a fair amount of landscape type stuff with large meshes that are usually
in a geographic projection, which can dump objects out past the million cutoff
point in 3ds. Usually these meshes can be 20 or 30 square miles, and I have
place small objects (many thousands) in the scene, and not experienced any
distortion, no matter how I may twist, distort, or rotate the small objects.
It would be nice for 3ds not to stop at a million, though. It gets kind of
annoying to not be able to track the coords at times. I don't have the option
of moving it, because it has to match our mapping stuff.
Oh, and there is the face limit per object, too, but I know that one is going
bye-bye, so it doesn't frustrate me as much as it used to.
Well, I didn't experience it either until Don Newlands brought up that issue
during the Studio City scaling ( yes, it's alive !). I even couldn't replay the
effect until I pushed a really small object far, far out and THEN rotated it.
Michael
Actually, after I downloaded the image that showed what the distortion looked
like, I realized that I have experienced this particular gremlin. I didn't know
what the heck was causing it, as it only seemed to happen with merged objects,
or at least that is what I thought.
I never bothered to mention it, since I never paid enough attention to when it
happened because I never saw it happening right away, and I never bothered to
try to reprduce it. That and I figured I'd get the party line about "checking
your system for viruses, blah, blah,", and I know my copy isn't cracked, so it
wasn't that, either.
Now I know. My life is complete 🙂
Always glad to fulfill your destiny <g>
The bottom line here is that using single precision halves the size of the
scene and the amount of memory required to store it. You'll just have to work
within the constraints of the system.
– G
>> work within the constraints of the system.
Thats what I try to push all the time….<g>.
No bickering meant, I just wanted to share an oddity we discovered.
Michael