Representation of crime scenes as virtual reality 3D computer displays promises to become a useful and important tool for law enforcement evaluation and analysis, forensic identification and pathological study and archival presentation during court proceedings. Use of these methods for assessment of evidentiary materials demands complete accuracy of reproduction of the original scene, both in data collection and in its eventual virtual reality representation. The recording of spatially accurate information as soon as possible after first arrival of law enforcement personnel is advantageous for unstable or hazardous crime scenes and reduces the possibility that either inadvertent measurement error or deliberate falsification may occur or be alleged concerning processing of a scene. Detailed measurements and multimedia archiving of critical surface topographical details in a calibrated, uniform, consistent and standardized quantitative 3D coordinate method are needed. These methods would afford professional personnel in initial contact with a crime scene the means for remote, non-contacting, immediate, thorough and unequivocal documentation of the contents of the scene. Measurements of the relative and absolute global positions of object sand victims, and their dispositions within the scene before their relocation and detailed examination, could be made. Resolution must be sufficient to map both small and large objects. Equipment must be able to map regions at varied resolution as collected from different perspectives. Progress is presented in devising methods for collecting and archiving 3D spatial numerical data from crime scenes, sufficient for law enforcement needs, by remote laser structured light and video imagery. Two types of simulation studies were done. One study evaluated the potential of 3D topographic mapping and 3D telepresence using a robotic platform for explosive ordnance disassembly. The second study involved using the laser mapping system on a fixed optical bench with simulated crime scene models of the people and furniture to assess feasibility, requirements and utility of such a system for crime scene documentation and analysis.
The use of conventional video cameras at standard broadcast rates permits 30 frame per second videocapture and recording. Even when moving events are recorded with fast shuttering to preclude blurring (e.g. 1000th second) each recorded consecutive stopped action still has a 33 millisecond interval between them. The reason for this is the finite time necessary to serially dump recorded information from the microchip sensor, and reinitialize the sensor for the next capture event. By designing a parallel video chip with multiple, independently capable segments for sensor input/output/re-initialization, the duration of the interval required for unloading and resetting the entire sensor is decreased by the number of discrete segments in the chip, and the number of unloading ports to transfer data. Silicon Mountain Design, Inc. (SMD) developed a 16 parallel channel output 512 by 512 by 8 bit digital video camera, and a suitable memory buffer to absorb 256 full images. This camera has the uniquely advantageous feature that no image data is absorbed while the camera discharges its image to the parallel output ports. With this parallel video camera it is possible to record events at 1000th second (or faster) continuously, or at least until the memory buffer fills. The use of structured light stereo numerical camera technology requires the collection of a series of video images, each video-image containing a different 'exposure' of an object with a different pattern of structured laser beams projected onto it. The complete series of images creates a temporal-spatial encoding of the laser beams necessary to calculate a 3-D numerical recreation of the object. By using a parallel video camera, the collection of a complete series is limited by the time it takes to expose each video-image, plus the time it takes to change the light pattern being projected. Using a rapid ferric liquid crystal electro-optic modulator with a 1 millisecond cycle time, and an SMD parallel video camera cycling at 1 millisecond, each pattern is projected and recorded in a cycle time of 1/500th second. An entire set of patterns can then be recorded within 1/60th second. This pattern set contains all the information necessary to calculate a 3-D map. The use of hyper-speed parallel video cameras in conjunction with high speed modulators enables video data rate acquisition of all data necessary to calculate numerical digital 3-D metrological surface data. Thus a 3-D video camera can operate at the rate of a conventional 2-D video camera. The speed of actual 3-D output information is a function of the speed of the computer, a parallel processor being preferred for the task. With video rate 3-D data acquisition law enforcement could survey crime scenes, obtain evidence, watch and record people, packages, suitcases, and record disaster scenes very rapidly.
KEYWORDS: Robotics, 3D acquisition, Video, 3D displays, Data archive systems, Video surveillance, Data acquisition, Virtual reality, 3D image processing, Inspection
We describe a system for rapid and convenient video data acquisition and 3-D numerical coordinate data calculation able to provide precise 3-D topographical maps and 3-D archival data sufficient to reconstruct a 3-D virtual reality display of a crime scene or mass disaster area. Under a joint U.S. army/U.S. Air Force project with collateral U.S. Navy support, to create a 3-D surgical robotic inspection device -- a mobile, multi-sensor robotic surgical assistant to aid the surgeon in diagnosis, continual surveillance of patient condition, and robotic surgical telemedicine of combat casualties -- the technology is being perfected for remote, non-destructive, quantitative 3-D mapping of objects of varied sizes. This technology is being advanced with hyper-speed parallel video technology and compact, very fast laser electro-optics, such that the acquisition of 3-D surface map data will shortly be acquired within the time frame of conventional 2-D video. With simple field-capable calibration, and mobile or portable platforms, the crime scene investigator could set up and survey the entire crime scene, or portions of it at high resolution, with almost the simplicity and speed of video or still photography. The survey apparatus would record relative position, location, and instantly archive thousands of artifacts at the site with 3-D data points capable of creating unbiased virtual reality reconstructions, or actual physical replicas, for the investigators, prosecutors, and jury.
The use of image processing is becoming increasingly important in the evaluation of violent crime. While much work has been done in the use of these techniques for forensic purposes outside of forensic pathology, its use in the pathologic examination of wounding has been limited. We are investigating the use of image processing and three-dimensional visualization in the analysis of patterned injuries and tissue damage. While image processing will never replace classical understanding and interpretation of how injuries develop and evolve, it can be a useful tool in helping an observer notice features in an image, may help provide correlation of surface to deep tissue injury, and provide a mechanism for the development of a metric for analyzing how likely it may be that a given object may have caused a given wound. We are also exploring methods of acquiring three-dimensional data for such measurements, which is the subject of a second paper.
The use of image processing is becoming increasingly important in the evaluation of violent crime. While much work has been done in the use of these techniques for forensic purposes outside of forensic pathology, its use in the pathologic examination of wounding has been limited. We are investigating the use of image processing in the analysis of patterned injuries and tissue damage. Our interests are currently concentrated on 1) the use of image processing techniques to aid the investigator in observing and evaluating patterned injuries in photographs, 2) measurement of the 3D shape characteristics of surface lesions, and 3) correlation of patterned injuries with deep tissue injury as a problem in 3D visualization. We are beginning investigations in data-acquisition problems for performing 3D scene reconstructions from the pathology perspective of correlating tissue injury to scene features and trace evidence localization. Our primary tool for correlation of surface injuries with deep tissue injuries has been the comparison of processed surface injury photographs with 3D reconstructions from antemortem CT and MRI data. We have developed a prototype robot for the acquisition of 3D wound and scene data.
In 1979 we first reported progress on a unique 3-D quantitative mapping structured light method to rapidly and remotely interrogate an unknown surface with an array of laser beams and to observe and measure the 3-D surfaces off-axis with one or more videocameras. -''2 Significant progress has occurred recently to make this method practical and cost-effective. The system consists of: 1) at least one passive sensor typically a 512 X 512 square pixel lowlight-level CID image intensified progressive scan videocamera operating at 30 Hz 2) an off-axis active structured laser projector using a 532nm doubled YAG solid state polarized laser beam formers and a prismatic optic to simultaneously generate a 128 X 128 square laser beamlet array 3) a spatially programmable light modulator to block or transmit selected sets of 128 rows (or 128 columns) of laser beams (corresponding to the generated array) at millisecond frame rates 4) optics to project the structured light sets onto the object 5) optics at the sensor end 6) positioning equipment to manipulate the object as required 7) suitable image processors array processors and computers for signal and image processing calculation of tables of X numerical data interactive display and archiving 8)interfaces to other CAD/CAM systems for the replication of surfaces or the reconstruction of multiple surfaces into geometric forms. .
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