Building a sky bridge

[Patrice Merchi]

I am attempting to build a floating bridge that crosses the border from one sim to another I belong to both groups, parcel permissions are the same. The issue is border lag instantly makes the prim/sculpt phantom when you cross the line and you fall. Is this a case of having to make two bridge halves and meeting at the sim edges? (Technically making a floating mountain using a log as the bridge to the next parcel and rock.)

Thanks for any ideas.

[Rolig Loon]

You have rediscovered the old sim-crossing bridge problem.  Basically, it's this:  An object only exists in the region where its root is.  Therefore, if you make a bridge and put its root in region A, you can walk on it as long as you are either (1) in region A yourself or (2) very recently in region A .  If you approach the same bridge from region B -- the region on the other end of the bridge -- the bridge doesn't know that you exist.  You fall through.

The solution takes many forms.  The simplest is to build two bridges, one in region A and the other in region B, and superimpose them, being sure that each has its root in the appropriate region.  In a more complicated structure, you can get away with simply adding a pair of transparent prim overlays on the roadbed of the bridge.  Offset them just enough from each other so that one is centered on the A side and the other on the B side of the boundary.  Whatever you do, do NOT link your two structures.  They must be separate from each other in order to remain in their proper regions.  Do it wrong and one of them may actually vanish for parts unknown.

Edited March 1, 2019 by Rolig Loon

[Chic Aeon]

Did you try anchoring the bridge to a single sim and letting it go into the adjoining one --- like an off sim lighthouse or surround? 

Never mind. Tried it. Doesn't work even with a prim :D.  And two "meeting" halves doesn't work either. I'd try Rolig's idea

 

Edited March 1, 2019 by Chic Aeon

[Love Zhaoying]

6 minutes ago, Chic Aeon said:

Did you try anchoring the bridge to a single sim and letting it go into the adjoining one --- like an off sim lighthouse or surround? 

Never mind. Tried it. Doesn't work even with a prim :D.  

 

Not even if you own both prims?

[Love Zhaoying]

9 minutes ago, Rolig Loon said:

Do it wrong and one of them may actually vanish for parts unknown.

Coordinates 0,0,0 sometimes! 

[Chic Aeon]

2 hours ago, Love Zhaoying said:

Not even if you own both prims?

Yep. Tested twice

[ChinRey]

1 hour ago, Chic Aeon said:

Yep. Tested twice

It's even listed in the Formal requirements for becoming a *real* builder

Quote

• Send you build off so far into the distance it's lost forever (may give up to three points: one for doing it manually, one for doing it with a script and one for doing it by unlinking across a sim border).

(It's the unlinking across a sim border that is the relevant part here.)

But seriously, I think Rolig explained the reason for the problem but if you want more details or a more concrete description how to solve it, let us know.

[animats]

Quote

In a more complicated structure, you can get away with simply adding a pair of transparent prim overlays on the roadbed of the bridge.

Yes. That's the usual solution. Look at a Linden road where it crosses a sim boundary with Advanced->Highlighting and Visibility->Highlight Transparent turned on. You'll usually see transparent but solid support prims reaching from each side to the other side.  Each support prim must reach off the edge of the sim (4 meters or so is about right) with its root on the sim. Has to be done on both sides of the boundary.
A well built region crossing.

You can fall through the railroad bridge on the right, though, if you walk over it in one direction. Trains are OK; the rails have support.

(How well roads are patched seems to vary by continent. Corsica is very good. Heterocera is mostly good, except for the road inside the Great Wall. Sansara varies. Kama City in Zindra is terrible. Which is why I build bikes that hover briefly during region crossings rather than sinking.)

[Chic Aeon]

I actually TESTED the single prim bridge theory and still fell through (a few times). This with a single one piece prim that wasn't even transparent and crossed from one sim to another. So I think Rolig's idea is probably the best.  

EDIT: Note that the picture with the ROAD is not a BRIDGE. I made mine elevated thinking that is what the OP wanted. You can't actually fall THROUGH the ground LOL. 

Edited March 2, 2019 by Chic Aeon

[Rolig Loon]

37 minutes ago, Chic Aeon said:

EDIT: Note that the picture with the ROAD is not a BRIDGE. I made mine elevated thinking that is what the OP wanted. You can't actually fall THROUGH the ground LOL. 

That's a really good point, which raises another perfectly good solution.  If your "bridge" really isn't a bridge, don't worry about it. Just be sure that the top surface of your structure is almost at ground level so that you don't fall through it and sink to your knees.  That's the situation that animats was talking about.  If you have done that, you don't need the extra prims.  Thing is, most people who make roads don't do it that way.  The road is either sitting on top of the ground or the builder has dug a trench under it to keep the ground from poking through.

[animats]

Bridge across a sim crossing. The road has been de-rendered so you can see the transparent support prims.

One prim must belong to each region and extend into the other region. The easiest way to do this is usually to make the support prim a child prim of a piece of the road. The center of the root prim determines which region owns the linkset. Child prims always belong to the same region as the root prim.

Since the support prims are below the road surface, you sink a bit when crossing this. Not much. But you don't fall through.

There are Linden bridges you can fall through, very old builds in Sansara. There are also some roads in the Snowlands where you can fall into a hole about 2m deep. I got LL moles to fix a few of the worst spots.

Edited March 2, 2019 by animats

[Chic Aeon]

1 hour ago, animats said:

One prim must belong to each region and extend into the other region. The easiest way to do this is usually to make the support prim a child prim of a piece of the road. The center of the root prim determines which region owns the linkset. Child prims always belong to the same region as the root prim.

Just saying that my testing today did not support this premise as I fell though a single elevated prim AT the sim crossing. It might depend on the sim.  I do understand the method.   I had a similar issue when I built a two sim dance area for SL14B.   I changed the design to solve the problem. 

[Patrice Merchi]

I followed the original instructions and it did work! But only one way. I changed the angles and overlap of the two sculpts and it solved the problem. I kind of suspected that's what I had to do. Thanks for the great instructions everyone!

[animats]

Bridge across a sim crossing. This is in Sandbox Bricker / Sandbox Colborne for the next 4 hours. Come take a look.

The sim boundary is halfway across the bridge. The back grey bridge just has two prims for the bridge, and avatars will fall through.

The front bridge has extra support prims. The top prims are root prims, and the prims underneath of the same color are child prims, located in the other sim but belonging to the sim of the root prim. This strange situation is what you want. The prims underneath give support as the avatar goes off the edge of the sim, until the handover to the new sim happens. That takes about 1 meter, more for fast vehicles in laggy sims.

The prims underneath could be transparent and they could be moved up to be at the road level. That would give you seamless support. That's what's usually done.

You don't have to push the child prims entirely into the other region. I just did that to make the picture clearer. Just having them stick over the boundary by 4m or so is enough. Easier to position, too, because you can't type a position bigger than 256 or below 0 into an object position, even though you can drag beyond that point.

Key point: you must have support from each sim for about 4m into the other sim.