Pratt, D., A Software Architecture for the Construction and Management of Real-Time Virtual World, Dissertation, Naval Postgraduate School, Monterey, CA, June 1993.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....possible image [7] using distance from the viewpoint as a decision metric [36] and using hybrid metric functions [11, 13] None of this work has addressed transparent objects in the scene. Most virtual world or simulation systems use a location based approach to segmenting the terrain model [11, 13, 20, 36, 37]. Typical data structures are grids and quadtrees. The grid approach has a single level structure based on a single resolution. The quadtree approach is based on a recursive subdivision of space, wherein each area is divided into four quadrants recursively until reaching some minimum resolution. ....

Pratt, D., A Software Architecture for the Construction and Management of Real-Time Virtual World, Dissertation, Naval Postgraduate School, Monterey, CA, June 1993.

....entity will be immersed. 3.1 The virtual entities The virtual entity is undoubtedly a central notion in a VE. Unfortunately, its definition can slightly vary from a system to another one. For example, AVIARY [Snowdon et West 1994] implements autonomous and communicating objects whereas NPSNET [Pratt 1993] provides semi automated forces (SAF) and autonomous Agents. We represent virtual entities as a set of modules, each one corresponding to a particular aspect of objects in virtual worlds. The Appearance corresponds to the description of the geometry of the entity. It also refers to any ....

D.R. Pratt. A Software Architecture for the Construction and Management of Real-Time Virtual Worlds. PhD thesis, Naval Postgraduate School, Monterey, California, June 1993.

....of a single node of a virtual reality system. It illustrates the power of the approach for providing simulation results which are applicable to all values of the variables in the system.The model is that of the software running on a single machine of the well known NPSNET virtual reality system [14]. The relationships between the components of the system are illustrated in Figure 5. The interactive performance of the single node is of interest, inter processor communication is modelled very coarsely. The model for this is given in Appendix A.2. The variables D, S and R represent the time ....

David R. Pratt, A Software Architecture for the Construction and Management of Real-Time Virtual Worlds, PhD Thesis, Naval Postgraduate School, Monterey, California, June 1993.

....the scalability of a virtual environment, both in terms of the number and complexity of objects, and number of users. Previous research in this area has increased the scalability of the number of objects within an environment, using techniques such as collision prediction [7] and dead reckoning [5]. Other work on scalability issues include data distribution management [2] aggregation [11] and dynamic multicast groups [4] In addition, recent advances in communications technologies have led to increased bandwidth, using higher bandwidth links, compression hardware and faster routers. ....

D. R. Pratt, "A Software Architecture for the Construction and Management of Real-Time Virtual Worlds", PhD Thesis, Dept Comp. Science, Naval Postgraduate School, CA, 1996.

....Since finer details are less pronounced, they need not be rendered and may be left out of the model thereby putting fewer polygons into 6 the graphics pipeline, allowing for higher frame rates. Important to note is that when polygons transform to less than one pixel, they effectively combine [DRPRATT1]. As distances increase, this natural occurrence aids in reducing visual detail and supports the use of LOD models. Several factors should be considered when rendering visual icons. Environmental effects such as clouds, fog, smoke, and haze will further reduce a viewer s perception of an icon and ....

....is the same. As shown in Figure 2, the icon rendered, i.e. high LOD, medium LOD, or low LOD, Eye Far Clipping Plane Point Constant sized objects in world coordinates Increasing distance from view point 7 is chosen based upon which bin the distance from the view point to the icon falls [DRPRATT1]. Figure 2. Level of Detail Ranges Although this appears to be a simple switch based upon distance, there is no exact algorithm to determine where or when the switch should occur. Trial and error seems to work best. There are some rules to follow to help in this determination. Most important High ....

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Pratt, David R., "A Software Architecture for the Construction and Management of Real-Time Virtual Worlds," Dissertation, Naval Postgraduate School, Monterey, CA, June 1993.

.... as shown in Figure 11,are the vehicle mock up with individual crew stations, a low resolution (by 1995 standards) Computer Image Generator (CIG) a static scene database (e.g. terrain) a host computer for display list generation and processing the simulation application, and an Ethernet network [109]. These elements have been adopted by a number of VEs and continue to be standard architecture in the DIS world. Commercial VR arcade systems, like Battletech, have adopted the LAN networked architecture [80] The principles of SIMNET are: No central computer is used for event scheduling. Each ....

....last update (nominally five seconds) When the updated posture (location and orientation) and velocity vectors are received by the Ghost object, the Ghost s is corrected to the updated values and resumes dead reckoning from this new posture. Figures 12 to 17 demonstrate how dead reckoning works [109] [59] The primary purpose of the Ghost concept is to reduce network traffic by minimizing updates at the cost of extra computation by the host system. Analysis of this method has confirmed that it works well with a wide variety of simulated vehicles with different performance characteristics, ....

Pratt, David R., A Software Architecture for the Construction and Management of Real Time Virtual Environments, Dissertation, Naval Postgraduate School, Monterey, California, June 1993.

....significant variances depending on scene complexities, levels of details of objects, rendering algorithms used, etc. This variance, if uncontrolled, may result in jerky movements during certain sequences of simulation, and could give the users so much confusion about the current simulation state[9]. We summarize this problem as follows. Problem 1 (Intra platform frame rate variance) Large variance of frame rates makes a user out of synchronization with the virtual world. To partly cope with this problem, many previous VR games on PC, e.g. id Software s DOOM[4] defined the worlds with a ....

....when users lists maintained by all hosts are nearly the same dif4 Figure 6. a) Message format (b) Message exchange protocol fered by only small fraction of time interval. To keep them synchronized, all host must broadcast the updated information of local user in a packet format like Figure 6(a)[9]. Connection between hosts are established by a simple handshaking procedure to correctly include the new participant to the users list. After the session is established, update messages are continuously exchanged to inform change of user information (Figure 6(b) When a brute force broadcasting ....

D. R. Pratt. "A Software Architecture for the Construction and Management of Real-Time Virtual Worlds". PhD thesis, Naval Post Graduate School, 1993.

....In addition to the standard Performer structure outlined above, NPSNET forks two additional processes to run in parallel with the Performer application, the Flight Control Stick (FCS) input process and the network communications process. A more detailed description of NPSNET can be found in [PRAT93][ZYDA93] C. RECENT RESEARCH Research associated with the NPSNET project is as varied as the backgrounds of the students involved, which span multiple armed service branches, and multiple warfare 7 specialties within each branch. One recent accomplishment has been the development of real time ....

Pratt, David R., "A Software Architecture for the Construction and Management of RealTime Virtual Worlds," Doctoral Dissertation, Naval Postgraduate School, Monterey CA, June 1993.

.... research with previous versions of NPSNET has also caused us to conclude that the development of a software architecture for a real time distributed environment requires a multifaceted approach to tackle these issues while adding an additional goal: reducing the per person cost of the simulation [Pratt93] C. Software Testbed for Solutions The NPSNET IV networked virtual environment, developed at the Computer Science Department of the Naval Postgraduate School (NPS) in Monterey, California [Zyda94] is our primary experimental testbed in this effort. Furthermore, we have been exploring new ....

Pratt, David R., A Software Architecture for the Construction and Management of Real Time virtual environments, Dissertation, Naval Postgraduate School, Monterey, California, June 1993.

....were locally designed to transmit information. They were in ASCII format so packet lengths were disproportionately long for the amount of information they contained. This did not present a problem for a distributed simulation on a very small scale. This scheme was used in NPSNET Versions 1 and 2 [Prat93]. The protocol did not require privileged access, but it did not comply with any standard, therefore it restricted use of NPSNET to the local LAN segment. Another developmental effort of NPSNET was the NPSStealth. NPSStealth is a version of NPSNET that integrated a translator for the SIMNET ....

....that a simulation host used at peak packet transmission rates. Packet transmission rates and, thus, offered load depends on the number of hosts, the number and type of entities, the scenario, the dead reckoning algorithm and thresholds, and the activities in which entities are engaged [IST93c][Prat93]. Our simulation hosts were used for man in the loop and semi autonomous simulations. Man in the loop simulation hosts model a single high performance aircraft and its weapon systems (gravity bombs, missiles, and guns) The aircraft models were not physically based and, thus, were capable of ....

Pratt, David R., A Software Architecture for the Construction and Management of Real Time Virtual Worlds, Dissertation, Naval Postgraduate School, Monterey, California, June 1993

....in networked games and multi user domains (MUDs) the server manages all the connections and rapidly becomes an input output bottleneck. Dead reckoning The networking technique used in NPSNET IV, evolved from SIMNET, and embodied in DIS follows the players and ghosts paradigm presented in [1][7]. In this paradigm, each object is controlled on its own host workstation by a software object called a Player. On every other workstation in the network, a version of the Player is dynamically modeled as an object called a Ghost. The Ghost objects on each workstation update their own position ....

Pratt, David R. "A Software Architecture for the Construction and Management of Real Time Virtual Environments". Dissertation, Naval Postgraduate School, Monterey, California (June 1993).

....in Computer Science, military operations from battle to replenishment can now be simulated on computers, and personnel can complete many phases of training in simulated battlefields, thus mitigating the expense of engaging in the real world environment. One such simulated battlefield, NPSNET [PRAT93], has been developed by the Computer Science Department of the Naval Postgraduate School (NPS) NPSNET is a lowcost, distributed, interactive, virtual 3D world for simulation and training. Personnel in the simulated environment interact with each other as if they were on a battlefield. They can ....

Pratt, D., A software Architecture for the Construction and Management of Real-time Virtual Worlds, PHD Dissertation, Computer Science Department, Naval Postgraduate School, Jun, 1993.

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Pratt, David R., "A Software Architecture for the Construction and Management of Real Time Virtual Worlds," Dissertation, Naval Postgraduate School, Monterey California, June 1993.

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