[vos-d] Online Space

[Peter Amstutz]

What are your thoughts about fixed-point numbers?  If have, say, a 16.16 
fixed-point number and the units are meters, you get a maximum range of 
65 kilometers with a resolution of about 15 micrometers (Reed mentioned 
notrons but in practice meters are the most useful for any kind of 
human-scale modeling).  I'm not a big fan of the "one coordinate system 
to rule them all" school of virtual worlds, I'm more interested in 
smaller spaces hyper-connected together relative to each other using 
portals, scene graph tricks (the contents of space A are embedded in 
space B at some offset) or just saying "the edge of this space is 
adjacent to this other space..."

I'm mainly concerned about the network-abstract representation, of 
course.  You still need to have tricks in the renderer (like continous 
recentering) to support huge-space schemes.

Also, with fixed-size sectors, I'm not sure how you would do a really 
huge area like the entire planet earth (although as we've established 
from the discussion, floating point numbers fair little better).  If you 
just connect the edges, that's still many many thousands of sectors.  
Perhaps one way of approaching at it is as a sparse-matrix problem or a 
hash space.

At any rate: coordinate systems are hard.

On Thu, Feb 01, 2007 at 10:01:57PM +0900, chris wrote:

> Don't know about vos yet but there is a general theory answer to this.
> For a space build on
> "modern floating-point variables", Ignoring the earlier part about a
> range from -1 to +1, there are some issues about floating point space
> you need to understand.
> 
> It is not possible with the conventional navigation rules people
> normally use: you will get
> jittery motion, rendering artefacts and other problems the further you
> go from the origin. Roughly speaking, things tend to vibrate a bit
> around 1-2,000m out then shake a lot more around 40,000m and it gets
> worse. Most ppl will tell you this sort of thing is due to limited
> precision. Although that is true it has a lot more to do with spatial
> resolution and spatial error.
> 
> To explain:
> Firstly, around 1.0 the resolution of floating point (x,y,z) space is
> very high: with the difference between one representable number and
> the next being 2.2 x 10^-16. As you get to the radius of the earth
> (about 6.4 x 10^6), the resolution is around 1m for single precision
> floating point coordinates. So the resolution of the space is
> nonuniform - see third slide in:
> http://www.web3d.org/x3d-earth/workshop2006/contributions/PingInteractiveGeoSimFidelityScalability.pdf
>
> [snip...]

-- 
[   Peter Amstutz  ][ tetron at interreality.org ][ peter.amstutz at gdit.com ]
[Lead Programmer][Interreality Project][Virtual Reality for the Internet]
[ VOS: Next Generation Internet Communication][ http://interreality.org ]
[ http://interreality.org/~tetron ][ pgpkey:  pgpkeys.mit.edu  18C21DF7 ]

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