Space-time imaging for secure environments.

October 99 News & Events

Intervid ,a recently listed company has focused on providing customised digital visual information systems to Lonrho Platinum Mines,Illovo Sugar and Johannesburg International Airport amoungst several others.Techtrix International,based at the University of Natal,s Innovation centre has joined forces with Intervid in a bid to fast track the development of novel technologies developed through several government initiatives in close collaboration with industrial partners.Here we describe some features which are finding wide application in security and environmental monitoring projects.

This report describes techniques developed for the secure management of both indoor and outdoor environments. These new technologies are impacting on machine vision applications across the board, from large-scale aerial imaging and security, down to novel gene scanning applications on the micro scale. Some of these technologies have already been deployed along South Africa's KwaZulu-Natal coastline and have been commissioned for deployment in Lonrho's platinum mines. The novelty of these projects is all the more remarkable in the light of cost-effective applications spanning the industry. It is interesting to note, that just as many of the significant developments in the industry stem from the integration of IT and security solutions, this multi-disciplinary approach is having a similar impact on solutions combining both environmental monitoring and security requirements.

Space-time imaging techniques

Objective measurements of environmental change over large areas can be cost effectively achieved using web enabled digital imaging techniques. Images can be projected onto detailed floor-plans for indoor applications or DTMs (digital terrain models) where secure coverage is required outdoors. These developments have led logically from the old aerial survey and mapping applications where the camera looked straight down. Now MapLock technology rapidly solves the more general case where any camera view is projected onto a 3D surface. This makes it possible to project images as well as various optical signatures and alarm conditions onto a map or geographic information system (GIS).

"It is interesting to note, that just as many of the significant developments in the industry stem from the integration of IT and security solutions, this multi-disciplinary approach is having a similar impact on solutions combining both environmental monitoring and security requirements."

Techtrix International has developed 3D imaging techniques that use multiple cameras to scan stationary or moving objects. One can, for example, unwrap the surface of an object to view both the front and back of the object at the same time. In the image below we have unwrapped a 2500-year-old vase and displayed it using a convenient projection. These techniques have been extended to security applications and public events. Even fashion shows where models are unwrapped and projected onto large screens above the ramp have recently received full-page newspaper exposure.

The relevance of the above montage or image mosaic becomes clear when one considers a continuous vigil from a camera mounted on a high point. Instead of rotating the object one can rotate the camera to create a 360° panorama or, by merely leaving it stationary, one can scan the evolution of a portion of any scene. This has been illustrated for a coastal view in Figure 2 tracking a set of swells approaching the coast. Wave period, approach angle and speed can be measured from these space-time images, sometimes known as a keogram. These systems have been deployed for both SAPREF and Sappi Saiccor while multi-million rand pipelines are being extended several kilometres into the ocean in order to warn engineers about dangerous sea conditions.

Environmental monitoring systems have been extended to include ship tracking near the Durban harbour entrance. By generating simultaneous orthogonal space-time plots (or keograms) one can measure both the horizontal and vertical positions of vessels as they approach the harbour. In the image below a tug crosses the bow of an approaching vessel. The wavy bow tracks the magnitude and period of vertical movement while the second keogram (immediately below the first) tracks the apparent size of the vessels and location of the tug. This is followed in the next image by a very clear measure of ship yaw. These records, like the black box in an aircraft, are very useful for scrutinising events should an accident occur.

Wide application in CCTV security systems

Surprisingly these technologies have wide application in CCTV security systems and have led to the development of SmartCam security systems. Significant movements, sometimes barely visible, are captured but these systems due to their ability to learn on the fly. SmartCams only take a few minutes to learn where activity occurs in the scene under video surveillance. After three minutes learning SmartCam will not only alarm on unusual activity, but will continually update where the scene under surveillance is relatively quiet and where it is busy without false alarming.

This means that even outdoor scenes with trees blowing in the wind and clouds casting shadows passing through the field of view, SmartCam systems adapt to changing activity levels without sensitivity to movement where security is concerned being affected. There is no tedious system set-up, no need to highlight foreground and background or areas of special interest - just a single click on the start detection button and the program will run in the background, only popping up when security related movement takes place.

Whenever this happens a short video clip including the run-up to the event is stored in your personal digital album. This time stamped visual evidence is then available for inspection both during and after the event. Hundreds of video clips are stored in the album with each being easily replayed or displayed frame by frame with a mouse-click on the album's thumbnail images.

Future impact of space-time imaging

In closing it is interesting to touch on the impact these technologies are having on the future. The image below includes a large scale model of the proposed Coega harbour intended for construction NE of Port Elizabeth. This model, built by the CSIR in the southern hemisphere's largest model hall uses wave generators for testing rival harbour designs to breaking point.

Realistic 1-in-50 year storms are generated to test proposed breakwaters and other coastal structures to their design limit. FlickerOptics techniques (see Figures 4b and c) have been used to record displacements of any of the 27 000 odd dolosse (the South African invention used the world over as concrete armour units in coastal structures).

Techtrix International has also recently tracked ship movement so as to select designs that are not only robust to major storm action, but which reduce the impact of wave action through the mouth more than alternate designs.

This imaging technology, used to measure all six degrees of motion for moored vessels (roll, pitch, yaw, heave, surge and sway) in the 100:1 scale model of Coega harbour at the CSIR's model hall. This work is now being extended to tracking ship movement in the vicinity of the Durban harbour where strong current gradients (both vertical and horizontal), coupled with large swells crossing the ships path during its final approach to the harbour entrance, are a concern to pilots and port engineers. In Figure 5 the cross current is measured from over two nautical miles from the Durban harbour entrance. These remote surface current measurements compare the position at which the bow passes a given point with the position of the ships wake three minutes later.

In the case illustrated here we have tracked the cross current displacing the wake of a ship. This keogram has been generated from 933 images recorded over 3 min 43,92 s, starting on the left hand side of the image, as the ship's bow passes through the sampling region, followed by the bulk of the ship silhouetted against the rising sun. Although the ship was over two nautical miles from the camera, both port and starboard bow shocks and associated waves are visible. The longer ocean swells can be clearly distinguished from the sea chop and the extent to which the wake has been displaced by a south bound cross current can be measured after known intervals as highlighted by the yellow line which has a slope of 0,4 m/s. This sea state information can be easily extracted by eye or by using 2-D fast Fourier transform techniques. Around the clock requirements are provided by radar based systems which work just as well after dark.

Clearly, real opportunities exist for adding intelligence to existing imaging systems and integrating both the environmental monitoring and perimeter security requirements when designing new generation digital solutions. It is interesting to think back a generation or two, when the suburban environment almost always had a record of events. Housewives could be relied on to keep a vigilant eye on events. Today with many double income families the home is often empty which means that not only is there more in today's crime conscious environment, but witnesses are often hard to come by, and few are willing to follow criminals to the dock ensuring due legal process. What is being outlined here is the inevitable role which intelligent imaging will play in bringing evidence to bare on personnel movement in the vicinity of a crime.

Solving problems associated with computer vision key to providing workable solutions

The central problems of computer vision, such as segmentation, stereo perception, recognition and so forth, have frustrated researchers for years. Solutions usually work only under highly constrained conditions, and even then are generally not computationally efficient, taking several seconds of computer time, and sometimes much more, to process a single image.

What hope is there then for frame rate processing?

Can nontrivial computations be done in real time to a video stream?

A quick calculation is depressing. One second of PAL video contains 25 frames of 768 x 576 pixels, roughly 11 million pixels. By today's standards, a desktop PC with a 330 MHz clock speed is considered reasonable. Such a PC would be able to devote 30 clock cycles to each pixel which is enough for a few simple operations, maybe a small convolution followed by a threshold, but not much more.

One approach is to use special chip sets that are optimised for common image processing operations, such as the fast Fourier Transform (FFT) or Wavelet image compression. These generally work very well and offer substantial speedups, but sometimes more flexibility is required.

Another approach is to reject the single CPU model. Computer vision is ideally suited for parallel processing, but there are still no parallel computers available that are cheap, easily programmed, and compatible with a wide range of hardware and software.

A simple strategy

A simple but effective strategy that can enhance any of the above approaches is to process only some of the pixels in each frame. Computation can be restricted to a region of interest, which might change size or location (or even shape) during the course of processing.

SmartCam has developed intelligent imaging systems to determine which portion of the field should be subject to space-time analysis. Once SmartCam has selected the regions of interest an image pyramid can be constructed, concentrating processing to higher levels of the pyramid, which have far fewer pixels. This allows computation intensive techniques to resolve complex features emerging from the scene.


These developments have extended beyond software development to the manufacture of new digital imaging systems. Space-time imaging techniques have led to the development of specialised panoramic imaging systems achieving 25 times the resolution of conventional cameras, opening the way for high resolution applications where detail and recognition are important. These include the new Skydar Systems available through InterVid and the High-Tec GeneScan systems being developed currently.

For further information contact Gavin Hough, tel: (031) 764 1285, e-mail: techtrix@

"SmartCam has developed intelligent imaging systems to determine which portion of the field should be subject to space-time analysis .... This allows computation intensive techniques to resolve complex features emerging from the scene."

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