Zonja Capalini

Reverse-engineering OARs: Understanding parcel maps

Format 0.2 Opensim Archives (OARs) include, since Opensim version 3c271b, a “landdata” directory that stores parcel data. For each parcel in the region there is a file in XML format in the directory. Amost all objects in Opensim are associated with a unique uuid that identifies them, and parcels are not an exception to that rule. Files in the “landdata” directory use the uuid of the parcel as their filename and have a “.xml” extension.

What’s inside each one of these .xml files? Let’s take a peek at a sample one:

    <?xml version="1.0" encoding="utf-16"?>
    <LandData>
      <Area>6256</Area>
      <AuctionID>0</AuctionID>
      <AuthBuyerID>00000000-0000-0000-0000-000000000000</AuthBuyerID>
      <Category>-1</Category>
      <ClaimDate>1255170099</ClaimDate>
      <ClaimPrice>0</ClaimPrice>
      <GlobalID>bfbf7bd4-7d7b-4a35-aba0-c352201cddcf</GlobalID>
      <GroupID>00000000-0000-0000-0000-000000000000</GroupID>
      <IsGroupOwned>False</IsGroupOwned>
      <Bitmap>AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAP//fwAAAAAA//9/AAAAAAD//38AAAAAAP//fwAAAAAA//9/AAAAAAD//38AAAAAAP//f
       wAAAAAA//9/AAAAAAD//38AAAAAAP//fwAAAAAA//9/AAAAAAD//38AAAAAAP//fwAAAAAA/
       /9/AAAAAAD//38AAAAAAP//fwAAAAAA//9/AAAAAAA=</Bitmap>
      <Description />
      <Flags>505454667</Flags>
      <LandingType>0</LandingType>
      <Name>Arrabal Tango Club</Name>
      <Status>0</Status>
      <LocalID>4</LocalID>
      <MediaAutoScale>0</MediaAutoScale>
      <MediaID>00000000-0000-0000-0000-000000000000</MediaID>
      <MediaURL />
      <MusicURL>http://xx.xx.xx.xx:8000</MusicURL>
      <OwnerID>69af4428-cec0-48d8-a0d9-c05268facca5</OwnerID>
      <ParcelAccessList />
      <PassHours>0</PassHours>
      <PassPrice>0</PassPrice>
      <SalePrice>0</SalePrice>
      <SnapshotID>00000000-0000-0000-0000-000000000000</SnapshotID>
      <UserLocation>&lt;0, 0, 0&gt;</UserLocation>
      <UserLookAt>&lt;0, 0, 0&gt;</UserLookAt>
      <Dwell>0</Dwell>
      <OtherCleanTime>0</OtherCleanTime>
    </LandData>

That’s the xml file for Arrabal Tango Club in Condensation Land — I’ve only obscured the music URL and wrapped the part between the <Bitmap> and </Bitmap> tags, which originally used only one line, with no intervening blanks. This string encodes the shape and position of the parcel in the region. How do we know that? Well, the parcel map has to be stored somewhere, and it has to be quite large, so the only candidate is the “Bitmap” string :-) Most probably this long string is a text encoding of binary data.

Indeed this is the case: the string is using the Base64 encoding (you can find that quickly by browsing the Wikipedia). After decoding the string, we get a binary chunk of exactly 512 bytes. I checked that all the terrain files have strings of exactly the same length, so this number had to mean something. Continue reading

December 18, 2009 Posted by | OpenSim, Tech News, Tutorials, ZOE | , , , , , | 6 Comments

ZOE version 0.1 released

Zoe

Zoe (Zonja’s OAR Editor) is a simple offline OAR manipulation tool that I wrote recently. You can find a detailed description of its functionality in my recent post “Moving and rotating OARs”. In this post I’ll describe how to install and use Zoe. I’ve designed Zoe with simplicity in mind, so that currently it only implements some very basic operations — by combining these operations, however, a number of pretty cool things can already be done. I’d love to get some feedback about the functionality of Zoe — at the end of the post I’ll list some of the things that I want to add to it, but I’m open to suggestions.

ZOE version 0.1 released
Continue reading

December 16, 2009 Posted by | OpenSim, Tech News, ZOE | , , | 15 Comments

Moving and rotating OARs [UPDATED]

[Update 20091216: ZOE v 0.1 has been released. You’ll find a manual and the download link here.]

…and some filtering too

Opensim Archives (OARs) are nowadays the standard tool to share and interchange full Opensim regions. Justin Clark-Casey, the core Opensim developer in charge of OARs, has lately added merge functionality to the loading of OARs. This means that you can merge (i.e., add) the contents of an OAR file to an existing region, without deleting its contents. This opens a plethora of interesting possibilities, but it also is the source of a lot of new problems. What if I’m very interested in merging an OAR with one of my existing regions, but I’d prefer the new contents to be placed differently from their original position? For example, I can be given an airboxed level at 1000 meters, but I might want to put it at 2000 m (for example, because I already have contents at 1000 m). Or I might be interested in an OAR with (say) some nice palace and gardens, but it’s located in the NE corner of the sim and I’d like to install it in the SW part of the sim.

At present, the “load oar” command does not allow for this kind of transformations. Indeed, it’s debatable whether Opensim should include code for this kind of application at all, or whether such manipulations should better be handled offline.

0705 - ZOE- A test run

In this article I present a very simple (and highly experimental) OAR manipulation tool called ZOE (for Zonja’s Oar Editor :-)) that implements some very basic forms of filtering, relocation and rotation for OARs as a whole.

Continue reading

December 14, 2009 Posted by | OpenSim, Tech News, ZOE | , , , , , | 24 Comments