In my previous post I gave a bit of information about some of the technology running behind the scenes at this year's Relay For Life held in the virtual world of Second Life®. The idea of using Portals to skip through sims that were offline.

Now that the event has passed, here's some info on what we observed.

The road that threads its way through 25 of the 32 simulators (sims are 255m² in surface area) was the single pathway for many avatars. It is a looped road, and with enough avatars walking along it I realised this closely resembled a highly-congested motorway. The following is a screenshot of the map of these sims, taken yesterday during a busy period. An explanation follows.

As you can see the road forms the shape of a capital letter "H", standing for Heroes and all the sims were named Heroes 1, Heroes 2, etc. accordingly. The direction of traffic flow around the road was in an anti-clockwise direction around the perimeter of the H shape. Each green dot represents exactly one avatar (note that dots overlap when avatars are very close proximity and therefore the dots may not add up to the actual numbers).

Highlighted in red are the 3 main hotspots we experienced for traffic jams. As more avatars poured into a traffic jammed sim, the worse it got for that sim, making it very hard for people to exit the sim. This is an issue that compounded itself once it got started. The effects of having so many avatars in one sim at the same time and walking creates a heavy load on the physics engine. If everyone was sitting still, it would be less of a problem, but the purpose was not to sit still here. The physics engine had so much processing to do that the physics "frames per second" started falling behind, causing what's known as time dilation - where all things start to go in slow motion (one of the aspects of perceived lag). Avatars moving in slow motion meant they couldn't maintain a steady flow. Avatars on the previous sims were walking at normal levels of physics performance until they walked into the lagged sims.

Now, in real life, we make use of traffic "parallelisation", "windowing" and "buffering" systems - using multiple lanes and round-abouts/traffic lights respectively. We could have used the built-in mechanism within Second Life that limits the maximum number of avatars per sim to prevent the build up in the first place. But the effects of using that feature would have two undesirable consquences:

1. It would send a virtual ripple of delayed traffic flow going backwards (clockwise) around the sims.
2. It would not suit our needs when events were being held in these sims to host many more seated avatars (remembering that seated avatars that are not moving require much less processing).

What we did, however, was make use of portals so that avatars could teleport through the laggy sim into the sim beyond it. We identified the sims with time dilation symptoms and manually enabled the portals before and after the affected sim. In 20/20 hindsight, we could possibly have automated this feature too.

The avatars in theory would then see the teleport portals and then use them to skip the affected sim. In practice, however, the human element came into play and the following observations were made:

1. Initially, untrained, the avatars would avoid the portal, perhaps thinking it was "griefer ware". We made repeated announcements via radio and estate messaging to say what these are there for and that they should be used if seen.
2. Once some individuals had become educated, they spoke to friends when they saw the portals and made group decisions on whether to weather the storm in the next sim or to teleport through.
3. Brave souls who weathered the storm (if it was really bad), or saw their friend(s) get stuck in one, thought twice about it the next time.  Survival of the fittest at its best!
4. Eventually, people made educated guesses as to whether or not to portal through - noting the numbers in the next sim and guaging from previous experiences.
5. Some of the people with more technical group titles above their head were always quick to click and portal through. Perhaps for the geek factor of it all?
6. People helped eachother.
7. Some got disoriented by the portaling process itself, sometimes coming out at the other end and walking the wrong way, back into the troubled sim they were trying to avoid in the first place. Note that the roads had arrow markings on them, but as feint watermarks. If you knew what to look for, or were handy with a map, you had no troubles, but ultimately it was less than intuitive navigation after a portal experience.
8. Nobody asked if when they use a portal, does their original "self" die and a new copy of the original self is created at the target location. This is because they know their "soul" (the user operating the avatar) is carried forward in the teleport, even if technically speaking the original avatar data is expunged from the one sim and copied to the target sim.

In general, the portals did help maintain the average flow of traffic without causing a backlog of traffic rippling through the other sims. A great success! 

I'll leave it at that, but mostly just enjoyed being fascinated by all the dots on the map, flowing around freely. Oh, and here's another screenshot taken today which gives a bit of info (but please see the official Relay for Life web site for released figures):