MetaVR's MDX 3D Terrain Database Format

MetaVR's first 3D visual terrain database format, initially developed in 1996 for its Virtual Reality Scene Generator (VRSG), was one of the first demand-paged visual database formats for PC-based image generators. The format's demand-paging allowed for the first time large-scale databases of high geometric density to be visualized on a personal computer at interactive frame rates; visualization of such high geometric density has long been a requirement of training simulations where terrain correlation is a critical requirement. Before VRSG and MDX were introduced, the real-time visualization of these databases required proprietary image generators costing hundred of thousands of dollars.

Real-time 3D visualization of MetaVR's virtual Baghdad, rendered in VRSG.

VRSG and MDX database technology enables training and simulation users to benefit from the rapid improvements in low-price PCs and PC 3D graphics accelerators. Within this customer base VRSG systems have been fielded as both "stealth" viewers and as out-the-window and sensor visuals for person-in-the-loop simulators.

MDX was developed specific to meet the requirements of mission-rehearsal simulations. Such simulations need the ability see long distances (that is, far horizon) and process massive amounts of geospecific imagery draped upon terrain elevation data.

MDX features

The MDX format and associated VRSG runtime software offer the following features:

• Demand-paged terrain geometry
• Demand-paged texture - MDX uses a tri-tiered virtual texture memory architecture, which allows asynchronous texture streaming from disk. Textures are swapped in from disk without a noticeable degradation in frame rate. This allows for databases with literally gigabytes of geographically specific imagery to be quickly loaded, rendered in real time, and traversed at fixed-wing aircraft rates using commercial graphics accelerators.
• Multiple terrain geometry levels of detail (LOD) allowing for DTED level one resolution databases to be visualized at 60HZ with up to a 40Km far clipping plane.
• Fully continuous terrain with vertex-by-vertex non-linear inter-LOD morphing technology. There are no distracting discrete changes in terrain LOD's. Terrain geometry morphing is undetectable while traversing the database at speeds of fixed-wing aircraft.
• Multiple texture LOD's for efficient utilization of texture memory and reduced swapping.
• Support for detail textures (microtextures) - Lower resolution geographically specific imagery may be modulated with very high-resolution geographically typical imagery for improved depth perception and sense of motion.

How MDX databases are produced

The MetaVR WorldPerfect virtual world creation application can output databases in MDX, OpenFlight, and ModSAF CTDB formats. The advanced features of the MDX are only available with the MDX output however. Elevation data is provided in DTED, ERDAS and several other formats. The 3D elevation data can optionally be fused with 2D imagery which can be either geographically specific (such as satellite or aerial photography), or geographically typical (theme-oriented textures repetitively tiled about the terrain). Imagery is input to WorldPerfect using the Windows BMP format as a standard imagery interchange format. This is due to the wealth of tools for personal computers capable of editing BMP images. Cultural features such as buildings and trees are easily added to the terrain.

Imagery from National Geospatial-Intelligence Agency (NGA, formerly NIMA) sources may be easily converted into BMP format by the GOTS freeware tool-set, NIMAMUSE. MetaVR technology is fully compatible with this freeware tool which may be downloaded directly from the NGA's Web site.

The NIMAMUSE Raster Importer program is used to extract imagery for input directly into WorldPerfect.

The following diagram illustrates the data flow to produce a geographically specific terrain database from the NGA NIMAMUSE products using MetaVR's rapid terrain creation and visualization technology:

MDX API

MetaVR provides to system integrators, on request, a free MDX Application Programmers Interface (API), which enables them to build their own databases for use with VRSG. Object files and a free example oflt2Mdx OpenFlight application executable with source code are provided free of charge. This library and any code it is linked with may not be redistributed without prior arrangement and permission from MetaVR. However, any MDX databases created with this API may be freely distributed without restriction or license from MetaVR.