VRSG Radar

MetaVR VRSG Radar enables the simulation of a radar system to be built upon the VRSG rendering engine, using Metadesic terrain tiles and moving models. VRSG Radar takes advantage of the capabilities of modern commercial graphics accelerators to solve real-time radar simulation problems that historically have required extensive custom hardware and software, at great expense.

VRSG Radar is suitable for building radar simulations such as the F16 Digital Radar Land Mapping System (DRLMS), synthetic aperture radar (SAR) displays for Unmanned Aerial Vehicles (UAV) or other such equipped platforms.

The image above shows MetaVR's DRLMS Radar Host example application, in which the simulated Radar uses a 60 degree sweep angle, a range of 20 nautical miles, at an elevation of 8200 feet. VRSG Radar is running on MetaVR's North America terrain consisting of with 3 arcsecond elevation data and .3, 1, 5, and 15 meter imagery covering a 10,480-geocell area. Also in this example, Radar Host and VRSG Radar are running at 120 frames per second, using commercial off-the-shelf personal computers.

VRSG Radar assists users in constructing a radar simulation by modeling the processes of the real radar system. Developers can create a radar host system that collects the raw radar return data from VRSG Radar and presents the data in a format suitable for the system being modeled. VRSG Radar handles the complexity of modeling the beam as it travels through space, impacts objects, and simulates the amount of energy that would be returned to the radar antenna.

Requirements

The hardware requirements for running VRSG Radar are similar to that of VRSG itself; it requires a DirectX 9-capable video card with a 32-bit per color pixel pipeline such as the ATI Radeon X1900 XTX, or the nVidia GeForce 7900 GTX cards. MetaVR recommends the Radeon X1900 XTX card as it has greater performance and has been tested more extensively.

VRSG Radar can run any set of Metadesic terrain tiles that you can run with VRSG. You can run the Radar Host on the same computer as VRSG Radar, but for best performance you should run it on a separate computer. The Radar host computer does not need to be a high-end system; it requires only basic 3D capabilities.

VRSG Radar uses the same visual database as the out-the-window channels, enabling perfect correlation with visual display. You can modify certain textures to augment their reflectivity in the radar spectrum, but the databases will remain perfectly geometrically correlated.

The image above shows VRSG Radar used in Zedasoft's simulated multifunction radar display in their cockpit application for Lockheed Martin's F-16 simulator. Image courtesy of ZedaSoft, Inc.

How VRSG Radar works

VRSG Radar works in conjunction with a user-developed Radar Host. The Radar Host models the position and orientation of the radar system, and the orientation of the beam relative to the platform hosting the radar system. As the Radar Host sweeps the beam in azimuth, it sends a request to VRSG Radar for the returned raw radar data corresponding for the current radar position, orientation, beam azimuth, beam dimensions, and maximum range. VRSG Radar responds with the set of summed intensities across the quantized range space. The Radar Host in turn processes this raw radar return data for display purposes.

The Radar Host must quantize the beam sweep in azimuth into discrete “looks” it sends to VRSG Radar for processing. Thus the fidelity in azimuth is related to the beam sweep rate, and the speed in which VRSG Radar and the radar host can process each look. VRSG Radar can typically support frame rates up to 300 Hz using modern PC hardware, so a beam sweep rate of 6 degrees per second can yield an azimuth resolution of as fine as 0.02 degrees per look.

For each radar look requested by the Radar Host, VRSG Radar quantizes the beam's vertical field-of-regard (FOR) into 131,072 samples. VRSG Radar casts 131,072 rays out into the scene distributed across the beams FOR and intersects these rays with database and moving model geometry, as shown in the diagram above.

At the first point along the ray where the terrain tiles or model geometry is intersected, VRSG Radar calculates the amount of energy that would be returned; it does so by considering the incident angle of the beam with respect to the local surface normal, in conjunction with the reflectivity of the intersected material. All these things are taken into consideration in simulating the amount of energy that would be returned to the radar antenna.

The range interval requested by the radar host is quantized into a set of range bins. The Radar Host requests the number of range bins using the Radar ICD. The number of range bins can vary from 256 to 4098 depending on the application. VRSG Radar returns to the host an array of intensities, where each entry represents the summation of all intensities of all the 131,072 samples that fall into that particular range bin. It is this array of summed intensities that the radar host processes into a displayable form. Because this approach mimics how a real radar system works, subtle radar characteristics such as shadows and bright spots on front-facing objects are a natural byproduct of the implementation.

Quantizing 131,072 samples 300 times per second is over 40 million rays cast per second. Although this might seem to be an unachievable amount of processing, VRSG takes advantage of the power of DirectX 9 programmable vertex and pixel shaders to make this possible on a low-cost Windows PC platform.

Example Radar Host applications

MetaVR provides two example Radar Host applications with full source code which illustrate how to communicate with VRSG Radar and prepare returned Radar data for display. You can use these applications as starting points for new applications or as examples for how to embed the funtionality into existing applications.

The DRLMS example illustrates the simulation of a radar system similar to that used by the F16 digital radar land-mapping system. The image at the top of the page is an actual screen capture of the DRLMS example Radar Host in action.

The SAR example application illustrates how you could create a real-time waterfall SAR display. Unlike the DRLMS example where a beam is swept left to right as the aircraft flies about, the SAR example holds the beam fixed to the airframe 90 degrees off-axis from the line of flight and collects data as it flies forward. Each new frame creates a scan line in a scrolling image, moving the old scanlines upward. This process creates the waterfall SAR display.

The image above is an example of the SAR example host in action, where the SAR example host is pointing the beam towards an airfield while flying forward. The building, fence, aircraft, and grid of tanks create shadows in the opposite direction of the beam. Also shown in this image, and most visibly on the building and aircraft, the faces that face the beam are brighter than those that do not.

The full source code provided with the example applications use Microsoft Foundation Classes for the graphical user interface and DirectX 8 for the Radar display. Although Direct3D is used for the graphical display in the example application, the VRSG Radar architecture is graphics-API independent. You can construct a Radar host on any platform using any graphics API.

The documentation for VRSG Radar is included in the MetaVR VRSG User's Guide.