If you arrived at this page from the ACM'97 Expo Exhibitors page, and would like infomation on our exhibit, ARC: Augmented Reality for Construction, please follow this link to its page.

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The ARC system is implemented using COTERIE, the testbed described here.

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COTERIE

The Columbia Object-oriented Testbed for Exploratory Research in Interactive Environments Blair MacIntyre, Steven Feiner

Motivating Requirements

1. Uniform treatment of local and distributed data
2. Embedded, interpreted language
3. Object-oriented, multithreaded programming model
4. Desirable distributed system characteristics (scalable, open, fault tolerant, network data transparency)
5. Data replication for fast local access
6. Asynchronous data propagation
7. Asynchronous notification of updates to shared data

Implementation

1. Network Objects
   The Network Object package supports distributed data sharing by providing remote method call facilities that are virtually transparent to the programmer. These include distributed garbage collection, exception propagation back to the calling site, and automatic marshalling and unmarshalling of method arguments and return values of virtually any data type between heterogeneous machines.
2. Obliq
   Obliq is a lexically-scoped untyped language for distributed object-oriented computation that is tightly integrated with Modula-3. Like Modula-3, it supports multiple threads of control within a single process. Obliq's distributed computation mechanism is based on Network Objects, allowing transparent support for multiple processes on heterogeneous machines. Objects are local to a site, while computation can roam over the network.
3. Obliq-3D
   Obliq-3D is a high-level 3D animation system that consists of two parts: a Modula-3 library that provides a set of graphical objects and animation primitives, and those same primitives embedded in Obliq. Obliq-3D programs can be written in Modula-3, Obliq, or any combination of the two because all data structures are simultaneously available from both languages. The package's structure and interface also make it relatively easy to extend.
4. HTTP
   The HTTP package is a Modula-3 library that support the creation of HTTP clients and servers. It was created as part of DEC SRC's Millicent project.

1. Shared Objects
   The Shared Object package, when combined with the Network Object package, provides a distributed language infrastructure geared toward the needs of VE applications by providing general purpose, asynchronously updated, replicated objects. It is based on two concepts: Distributed Shared Memory via the Shared Data-Object Model, and Callback Objects.
   • Distributed Shared Memory (DSM) allows a network of computers to be programmed much like a multiprocessor, since the programmer is presented with the familiar paradigm of a common shared memory. DSM mechanisms use message-passing protocols between machines to implement some model of shared memory access that is used by the programmer. The Shared Data-Object Model of DSM is particularly well suited to our needs since it is a high-level approach that can be implemented efficiently at the application layer. This model was introduced in the Orca parallel programming language. In this model, shared data is encapsulated in user-defined objects and can only be accessed through the objects' method calls. The DSM address space is partitioned implicitly by the application programmer, with an object being the smallest unit of sharing. The shared data is replicated in each process that is interested in the object. Each process can call any method of an object it shares, just as it can with a non-shared object.
   • Callback Objects allow the programmer to receive notification of changes to a Shared Object in an object-oriented fashion. For any Shared Object, an associated Callback Object exists with a similar set of methods which the programmer can subclass off of to receive notification of changes to a particular object instance.
2. Repo
   In Obliq, all objects are Network Objects: one copy exists in some process, and all other processes make remote method calls to access that object. In Repo, we round out the object model with the other two kinds of objects a programmer might need:
   • replicated objects (implemented with our Shared Objects)
   • simple objects (that are always local to the process using them)
   Repo is our superset of Obliq. A manual will be available soon.
3. Anim-VR
   The Anim-VR package is an rewrite of Anim-3D that aims to satisfy two important goals:
   • Efficiency. The internals of Anim-3D have been almost entirely rewritten to solve the efficiency problems of Anim-3D. Furthermore, a backend was written using Renderware to support NT and Windows95 machines without 3D accelerators.
   • VE Support. A number of features need by Virtual Environment systems have been added to Anim-3D. These include support for textures, line and polygon sets, 2D projection and picking calculations, support for nested coordinate system calculations, 2- and 3-D text, attaching of 2D windows to 3D points, etc.
4. Obliq/HTTP
   This package exposes the Modula-3 HTTP package into Obliq, allowing distributed HTTP servers to be written entirely in Obliq. This package was used to create our lab's Augmented Reality WebCam in less than 200 lines of code. This package also allows us to easily build applications with web-based interfaces.
5. Trackers
   We have developed an object oriented tracker package with support for a variety of 2, 3 and 6DOF tracking systems, including
   • Logitech Flying Mouse
   • Origin Instruments Dynasight
   • Virtual I/O Orientation trackers
   • 2D Microsoft protocol serial mice
   • Trimble GPS systems
   • the Spectrum RingMouse
   • Directed Perception Pan-Tilt units
   • standard BarCode scanners

   More devices are being added (ie. Ascension Flock of Birds, Precision Navigation Orientation Tracker). The package is designed so that client software can operate on any tracker with appropriate capabilities (2D, 3D position or orientation, or some combination) interchangeably.

Using COTERIE, we are building a library of objects to support the various VE devices we use and an application framework that allows us to create prototype applications with the distributed system characteristics we desire.

Current Status

• HP workstations, running HP-UX 9.0 (partially)
• SGI workstations, running IRIX 6.x
• x86-based PCs running Linux, NT 4.0 and Windows 95.
• Sun Sparcstations, running Solaris 2.{4,5}

• Any Unix workstation that supports X and OpenGL. For example, we use it on our SGI and Sun UltraSparc workstations using their accelerators, on Linux machines using various software OpenGLs, and on a variety of Unixen using Mesa, a free OpenGL-like library that runs on top of X windows.
• NT 4.0 (on x86 processors) and Windows 95, using OpenGL and Renderware.

• Calibration
  We are developing separate HMD calibration software for both video- and see-through AR systems.
• 2D Windows
  As with our previous work, we wish to position traditional 2D windows in the 3D world. Our current system supports this as well.
• Applications
  We are working on a number of prototype applications, both on our own and in conjunction with the Columbia Architecture School and Nynex Science and Technology.

Acknowledgments

This research is supported in part by the Office of Naval Research under Contract N00014-97-1-0838, a gift from NYNEX Science & Technology, hardware and software gifts from Mitsubishi Electric Research Labs, Intel, and Microsoft, the New York State Center for Advanced Technology in Computers and Information Systems under Contract NYSSTF-CAT-92-053, the Columbia Center for Telecommunications Research under NSF Grant ECD-88-11111, and NSF Grant CDA-92-23009.

References

MacIntyre, B and S. Feiner. "[Language-level support for exploratory programming of distributed virtual environments." In Proc. UIST '96 (ACM Symp. on User Interface Software and Technology), Seattle, WA, November 6-8, 1996, 83-95.