The straight dope on height limits?

From the Simulator wiki entry:
Objects may go off-world above 768m height.

Ok, so llSetPos can move stuff up to 512m. The normal building tools can move them up to 768. But I thought physical objects could go up to 4096 without going offworld... how exactly does this altitude thing work? Is it sort of like a sandbox, in that I can move stuff up there but it will be returned after some time?
They wont return anything if I am sitting on it, right? Like a vehicle?

If you are sitting on it it won't return.

***EDITIED to make secret again***

I've successfully placed a skydiving platform at 2000m and 4000m (so that people have something to stand on and set altimeters once they leave the elevator). Thus far they have not been returned.

Shhh Strife, dont spread that or the lindens will fix it.

On the other hand, an automated drop from the elevator (like at Abbotts Aerodrome) ensures that everyone is freefalling within chat distance of each other. It's hard to get several people to jump off a platform at the same time.

But that's good to know that platforms won't get returned from that height.

I can tell you that I have free fallen from a very,very,very,very,very high altitude. IM me if you want to know how high. I even have pics.

wizzie

I've gone 4k + with prim_pos. The prims stay where they stopped until I adjust their position/rotation. When I do that, they instantly jump to 512.

llSetPos() and the physical movement functions will take a prim up to 4095 meters, anything beyond that and it'll either get returned or just disappear. Objects attached to avatars are virtually unlimited (millions of meters, depending on how long you want to spend waiting to ascend that high.) Editing tools are limited to 768. And that is the straight dope.

Can anyone see any actual problems with allowing arbitrary object heights above one's plot? It's just a number after all, and as long as the machine representation of the value doesn't take up more bits of storage than required at normal altitudes (and that's almost certainly the case), it shouldn't really make any difference.

Managing one's objects does of course become more difficult when they're spread over large distances, but that problem is already here --- 1000m is pretty much unmaintainable by hand, and 100,000m would also be unmaintainable. The solution to maintainability is to provide plot owners with some decent query functions for their assets.

And "llSensor" does NOT qualify as decent.

They recently lifted the 512 meter cap?
==Chris

I just verified in old and new sims the 512 limit on llSetPos()

No they didn't. I interpreted his "and" to mean that we could use SetPos "and then" physics after reaching the SetPos height cap of 512.

I believe the limits are due to loss of precision in coordinates (looks like they are single-precision floats) and the "odd" effects that loss of precision can have at higher altitudes (higher z values). In a float, the number of bits used to represent the value remains the same regardless of how large or small the number is, therefore it has to lose precision as values get larger. This is why AVs distort, the camera gets jerky, and the name above AVs gets wonky at high altitudes.

However, it would be nice to be able to fly into space on a rocketship and take two passengers with me.

it's probably the precision issue, to store 0.001 you need 10 bit's of precision meaning the biggest your number can be is 2^13 or 8192. But i'm guessing the phisics engine wants more percision then that so it probably wants 11 bits of percision for the float portion. (course if they used double precision floats then this would be a non issue as they have 52 bits of precision; only problem is double percision math would be slower)

I think Strife's hit the nail on the head.

It won't be speed that restricts it. Modern-day CPUs run floating point ops as fast or faster than integer ops in some cases. The technology has seen staggering improvement. Also, we're talking about an interpreted VM here, so pretty much all arithmetic in scripts (not in the engines!) takes near-zero time compared to the overheads of the VM machinery.

In contrast, the details of IEEE 754 representation and ranges give it all away:

                              Binary               Decimal
Single Precision       ± (2 - 2^-23)^127         ~ ± 1038.53
Double Precision       ± (2 - 2^-52)^1023        ~ ± 10308.25

As Strife points out, 24 bits of mantissa aren't going to give you much precision if you want to live up at 100,000m. In fact, you'd probably notice the chaotic precision cycles down at 0.001m, not nice at all.

In addition, storage and transfer of doubles has an overhead compared to shorter floats of course, so maybe that's a second reason for the restriction.

It's a pity, I'd quite like to live in orbit, but only after they'd got rid of the dumb LOD so that I can see the curvature of the planet without having an FPS of 0.0.

In due course, they'll have to go to doubles anyway, it's part of evolution.

This isn't a planet, and there is no curvature
In SL the world really is flat

WooHoo it's true, it's true !! Long live Bert Rutan!!!! ETA Apotheus ???

Sad, isn't it.

That aside though, the same applies to a flat 2L world. We should be able to see the whole thing no matter how high we are without decrease in FPS because we're never asking for more detail than a screen's worth of pixels.

Whereas, with the current obsession with object-centric processing, setting our range of visibility to 100 kilometers would not be a good idea. I don't have the answers, but certainly starting from the objects instead of starting from the viewer has to be wrong. It needs a rethink, more in the direction of raytracing and voxels, because it's totally inappropriate to even consider an object for processing no matter how large it is if it's not the major contributor to shading a pixel on the screen.

I personally have gone up to 20k above ground, but not sitting on anything, simply flying up there, i teleported down since it was taking the freefall to much time. For Windows users, if you hold down 'Home' it will shoot you up until you let go!

(i have removed my post due to its inflammatory content and humbly apologize for it)

Pardon?

Eggy wrote:

> (i have removed my post due to its inflammatory content and humbly apologize for it)

Woah!

Update! The sim I had platforms at 2km and 4km crashed and reset. This seems to be when objects above 768 are cleared. However they are not returned. This may depend on permissions of the object or not. I don't really know. I DO know that my objects were not returned, but just silently deleted.