[Opensim-dev] Negative z values

[Melanie]

There are potential issues with code/tools written with the notion
that the metaverse indeed ends at 0, but I believe they can be overcome.
In this vein, there is another "feature" we may want to push for:

Raw files allow specifying a water height for each 4x4 m square, but
currently regions only have a notion of water level for the entire
region, taken from the 0,0 coordinate of the water level layer in
the raw file.

I believe full support for a water height map (including Z < 0
depths) would be an advantage of opensim over SL, as SL currently
struggles with basements, subway tunnels and mountain lakes.

- Melanie

On 25/04/2014 02:16, Jim Williams wrote:
> Seems to me that 0 is a completely arbitrary number and that a cut-off for
> any reason other than hardware/mathematical limitations is unwarranted.  I
> could see taking an "oh well" attitude about things that don't work with
> -z, but declaring the Metaverse to simply end at 0 seems very random.
> 
> 
> On Thu, Apr 24, 2014 at 6:46 PM, Melanie <melanie at t-data.com> wrote:
> 
>> I have never seen a Z < 0 build. I see lots of problems that may be
>> possible with this, but I think that quite beautiful and interesting
>> builds could make use of this and would support keeping it. The
>> change in the viewer is recent and likely trivial to undo.
>>
>> - Melanie
>>
>> On 25/04/2014 00:32, Justin Clark-Casey wrote:
>> > Hi folks.  Historically, whether by accident or design, OpenSimulator
>> has allowed negative Z values for terrain, objects
>> > and avatars (e.g. <130, 50, -45>.  I have seen people use this facility
>> to build fully underwater or partially
>> > underwater structures (e.g. oil rigs, sunken ships, etc.) which are
>> conceptually far below the water line without having
>> > to set that water line at a level that may be way above that of
>> surrounding regions.
>> >
>> > However, at least on Singularity 1.8.5 on Linux, fog effects do not work
>> properly when z < 0, where all view distances
>> > have very high fog no matter what the fog settings.  This may be a
>> recent change - I remember fog working properly at
>> > negative z values in the past, though the fog issue still occurred past
>> a certain -ve z.  There may be other issues of
>> > which I'm not aware.  Arguably, these are not bugs since the Linden Grid
>> does not allow z < 0 (though one could make the
>> > same argument for var regions, etc.).
>> >
>> > With in-world testing of current development code, BulletSim appears to
>> have a hard-coded check where I can't move my
>> > avatar below z == 2 whether terrain is z < 0 or not (this should
>> probably at least be fixed so z = 0 is possible).  ODE
>> > has allowed and still allows the avatar to descend to negative depths.
>> >
>> > One argument is that in the light of such bugs, it would be better to
>> consistently enforce z >= 0 and require people
>> > with -z builds to either move them and the water level up using
>> OpenSimulator commands (e.g. "translate scene") or never
>> > update their OpenSimulator installation.
>> >
>> > However, I think there is a real value in keeping the -ve z ability.  It
>> allows people to extend deep water builds
>> > without having to adjust any neighbouring sims for consistency (which
>> they may not have control over).  I'm sure it's
>> > possible to address the viewer-side issues.  OpenSimulator could have an
>> allow-negative-z flag which is false by default
>> > to make it explicit that using -ve z may have issues at this time.  I
>> accept this is a more complicated solution than
>> > enforcing z == 0, though enforcing z == 0 will also requires many
>> changes to the current code where bounds are not checked.
>> >
>> > If my experience is unusual and -z builds are very rare then there's
>> more of a case for enforcing z >= 0.
>> >
>> > Thoughts?
>> >
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> 
> 
> 
> 
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