768m build limit? BAH! Building at 3009m...

This is a test, this is only a test.

It appears the actual size of the buildable world that a sim can support, is far larger than anything we've been told publicly.

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The build height limit of 768 meters appears to be an arbitrary value chosen at random as "the highest we at LL think anyone would possibly want to build". But as shown here, the engine has no issues at all with building objects 3000 meters high.

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(The user-interface sort of supports building beyond 768 meters, but if I attempt to change any parameter the usual way, the UI will suddenly say "HEY, what the hell are you doing at 3000+ meters?!" and forces it down to the regular maximum of 768.)

It's too bad that LL has chosen to limit their engine in the way that they have, since the both the sim and the client are obviously capable of far more than what LL is currently permitting them to do.

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-Scalar

The higher you are the more visible are floating point precision problems. How's the prim drift at 3000m?

If you want to build up that high, the easier way is to fly a vehicle up there then rez in the vehicle.

There are accuracy issues at that height - the float for your z position is using up bits of precision saying "3000" rather than "300". Anecdotally, things are less stable even building around 750m as compared with nearer ground level - more weird prim drifts etc. Above the 768 limit there is higher prevalence of prims spontaneously vanishing.

So, yeah, I think the restrictions are mostly technical rather than "the highest we at LL think anyone would possibly want to build". If there were no restriction then people would build much higher and the prims in their skyboxes would be that much flakier.

Incidentally, the maximum it is possible to rez at is around 4000m.

I work at 700+ meters routinely, that's where I have my "lab", and I don't see problems with floating point round-off.

Well, if LL is using IEEE floating point and set the units to mms (which appears to be the case in the client) then you shouldn't have roundoff problems until you hit 8000m or so.

I really don't know how they handle coordinates though. It could easily be integer based in which case you wouldn't have roundoff problems (but would have a hard ceiling at 4M meters or so.

Well, there are a few issues with building above 768m, but it can certainly be done. I've had a build that resides at 4000m for a couple months now. (If you're interested, it's the SkyLounge, in the Garden of Mo, Louise. There's an elevator at ground level, at Louise (185,232).)

Yes, there is prim drift, not that you can edit anything usefully anyway (see below and prev. posts). Objects rezzed (by script, llRezObject) at even numbers (say 4000.000m) will in fact appear a few centimeters off the mark (say 3999.995m). Mildly annoying, especially if you're rezzing multiple objects in close proximity or where precision is required (there's a reason why all my furniture is to designed to float a fair bit above the floor).

Floating llSetText starts to develop a noticeable jitter at only a couple thousand meters. It's very minor, but noticeable. I've also noticed the occasional bit of camera bouncing here and there.

But, there's another point that causes more irksome problems. At some arbitrary elevation above ~767.9m, objects are deleted at odd intervals. Long-term non-physical builds can be problematic. I've not done any serious experimentation, but I can provide two data points: An object rezzed at 1000m lasted for a few weeks, while the SkyLounge (rooted at 4000m) is deleted every time there's an upgrade or grid reset (but apparently not when there's a simple sim crash). It's not overly difficult to come up with a scheme to periodically launch a sensor-enabled object up there, scan for the Lounge, and rez a new copy if it's been zotted. But it is another minor headache to deal with.

And, as mentioned above, if anything above 768m moves non-physically, or if it is moved with the edit tool, it will immediately pop to 768m. I've exploited this effect to make a 3,000m teleporter: the down elevator is a non-physical mover, so at the first hop it jumps over 3km down. Shaves a fair bit of time off the return trip, anyway.

Oh, the maximum unattached prim altitude is 4096m. Anything not attached to an avatar will be returned if its root prim exceeds this Z value. (I suppose one could make a long, skinny linked tower and push it above 4096m by a 20 or 30 meters, although I can't see any reason to do so, save for bragging rights.) This is true both of physical and non-physical objects. Vexingly true of vehicles, which will disappear and leave you to drop 4km to the ground.

Physics seems to have a much larger limit than that, but you can use cuts to build objects much smaller than a 1mm cube.
I've been over 2 billion meters and there were clear rounding problems (my avatar was badly distorted).