On Fri, Feb 09, 2007 at 04:56:39PM +0100, Karsten Otto wrote: > I am not quite sure what kind of precision is necessary here... I'd > expect that it should be enough to center the current sector for > displaying purposes, and re-center to the new sector once you cross a > portal boundary. Considering relatively small sectors, I'd imagine an > error factor of a few centimeters is not too disturbing when the > objects in question are 50 meters away. This is probably two pixels > difference on the average display resolution. I can live with that :-)
You've put your finger on it. From a rendering perspective, you just need enough precision so that the edges between two triangles that are adjacent will actually be drawn that way without visible seams or cracks. If you make sure the world is set up in such a way that the camera is never too far from the origin, then this isn't a problem. (Strictly speaking, the camera transform causes the world to be oriented around the camera, not to oriented the camera in the world -- but it's easier to speak about it as if it were the camera that is moving). Human scale is pretty easy to manage. Geospatial scale, and particularly moving between a galactic scale down to a human scale smoothly is where things are really difficult. I'm open to ideas as to how to split this, because frankly I don't know how best to compromise between a massive scale and a high-detail scale, particularly in terms of the representation that gets pushed over the network. Also, on the topic of precision, something else that hasn't been mentioned is cumulative error -- depending on how you work with your coordinates, you may start getting artifacts due to the accumulation of roundoff errors. This is fairly managable by having some immutable "source" data from which you do your transforms from, instead doing incremental transformations, but still something to watch out for. > Regarding physics simulation, which (if I understand you correctly) > suffers the most from matrix creep, well... I am no expert, but > couldn't you calculate this in a virtual coordinate space, derived > from the world coordinates in such a fashion that all objects > involved are close to the center? And then, once you reach some > "stable" result, convert the virtual coordinates back to world > coordinate space and continue from there? That may not be > particularly precise or realistic, but again, as long as the system > behaves more or less consistently, I can live with it. Hmm. Yes, you probably could do something like that, if you can divide up your interacting objects into isolated groups. Then you could simulate those objects independently at the origin, then transform them back to the original position. Seems like a hassle, though. In practice, precise consistancy is the *least* of people's worries when setting up a rigid body physics simulation; setting up the system takes a lot of tweaking just to prevent it from flipping out. Here's a harder question: how do you handle the physics for an object that's passing through or straddling a portal? -- [ Peter Amstutz ][ [EMAIL PROTECTED] ][ [EMAIL PROTECTED] ] [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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