One of the most interesting developments in Opensim lately have been megaregions. Megaregions are non-standard “big” regions created by combining several standard, 256×256 meters regions. For example, you can combine four standard regions in a square to get a megaregion of 512×512 m. Megaregions are very convenient because of several reasons: for example the usual lag in region crossings disappears completely (since you are in the “same” region), and the same is true of vehicles. On the other hand, megaregion support is still experimental, and a number of things that work in normal regions don’t work or work only partially in megaregions. For example, you cannot define parcels outside of the SW region (this is due to the way parcel maps work), and therefore you can’t have independent music streams (for example) when x > 256 or y > 256.
Diva Canto’s distribution of Opensim directly supports megaregions. You can also migrate an existing non-megaregion installation to a megaregion configuration, if you follow certain precautions. Migrating from a megaregion configuration to a non-megaregion configuration is also possible — you change the setting that implements megaregions, “CombineContiguousRegions” to false, and it works as expected.
OAR support for megaregions is partial: since technically all the objects in the megaregion are stored in the SW region, when you take an OAR of the SW region you get all the objects of the megaregion but only the terrain for that same region — this means that you cannot fully rebuild a megaregion from an OAR, which is a pity (you will be missing the terrain files for all regions except the SW one).
In this post I’ll describe some experiments I made with an OAR manipulation tool I developped following a suggestion of Stefan Andersson. The tool takes as its input a megaregion OAR and splits it into several non-megaregion OARs, creating one OAR for each region that constitutes the megaregion and has objects in it. This is so because megaregions may have holes, and when a possible region does not have objects there’s simply no information in the megaregion OAR about whether a it’s a region with no objects (for example, a sea-only region) or a hole in the megaregion.