What Actually Happens During a Region Crossing
A region crossing is a coordinated hand-off between two simulators. The viewer freezes your avatar and vehicle, collects a bundle of state data, compresses it, and sends it to the next region. That bundle includes:
- Avatar state
- Attachments
- Vehicle state
- Movement vectors
- Viewer‑side metadata (voice, music, draw distance, etc.)
A common misconception is that LI (Land Impact) or ARC (Avatar Render Cost) affects the amount of data transferred. It doesn’t. Only the UUIDs and state information are included in the hand-off.
However — and this is where the nuance matters — LI and ARC do affect the receiving region while the crossing data is processing. The region must load textures, meshes, and scripts associated with your avatar and vehicle as that info becomes available. That consumes simulator CPU cycles, especially when multiple avatars enter the region.
So while LI and ARC don’t affect the hand-off, they absolutely affect the landing.
Attachments List
Attachments are objects explicitly worn on an avatar (clothes, HUDs, weapons, etc.) and are linked to the avatar’s skeleton bones or HUD attachment points. When an avatar enters a region, the simulator builds and maintains a specific list of these attachments (mirrored in Linden Scripting Language (LSL) via functions like llGetAttachedList), and these objects are treated as part of the avatar’s state when moving between regions.
The data size of attachments does not affect the size of the list that needs to transfer. All the attachments are a UUID and state. As best I can tell all attachments are the same ‘size’ in the list.
An evening gown with 6,000 polygons and a mini-skirt with 1,000 polygons are the same size in the list. So it is the number of attachments not their size that affects the list and crossing.
Vehicles
Attachments and vehicles are treated differently. A boat, plane, car, or other vehicle you “sit” on is a normal in-world object owned by someone, with the avatar linked via sit-target, not via attachment points. The simulator manages that vehicle as a separate physical object, tracking its position, physics, and region-crossing behavior as part of the region’s object set rather than as a wearable on the avatar.
When you cross a region boundary in a vehicle, the simulator hands off both your avatar and the vehicle to the next simulator, but the avatar’s attachment list and the vehicle’s object data are separate logical packets/state groups in that hand-off. This is why there can be vehicle-specific crossing bugs (vehicle lost, snapped back, or de-physicalized) that do not affect your avatar’s worn attachments in the same way, and conversely why attachment failures in busy regions do not generally “turn your vehicle into an attachment” or vice versa.
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