The increasing demand The increasing for up-to-date 3D Geographic Information Systems (GIS) databases in many applications, such as town planning, transportation, and utility management, poses significant challenge to the Geomatics community. The data acquisition is one of the core problems for building and maintaining such databases. The information needed is expensive to obtain by conventional methods such as aerial photogrammetry and terrestrial surveying. These methods are, therefore, not well suited for rapid updating. The VISAT™ system provides a new avenue to meet this challenge. The VISAT™ system represents an innovative and disruptive technology for creating and updating 3-D GIS databases very quickly and inexpensively.

This VISAT™ system integrates a cluster of digital cameras, receiver of the Global Positioning System (GPS), an Inertial Navigation System (INS), and Distance Measuring Instrument to collect panoramic views along roadways throughout the project area. The VISAT™ system implements the idea of storing georeferenced digital images as the basic unit and of combining an arbitrary number of such image units (which may be from different time periods) to obtain the specific information required. The system can be used to selectively update GIS databases precisely, quickly, and inexpensively. The VISAT™ system operates at normal roadway speeds (up to 110 km/h) and easily achieves sub-meter accuracy for features captured in the images. This accuracy is achievable in all operational environments including obstructed areas where a stand-alone GPS is not reliable. Sensor integration has been optimized to reach the requirements of the survey market. The data flow has been streamlined to facilitate the subsequent feature extraction process and data transfer into a GIS system.

VISAT™ Navigation Component

The system’s data acquisition components include a Strapdown INS system, L1/L2 GPS receiver, 6 to 12 digital cameras, and an integrated DMI hookup on the speed sensor of the vehicle, and the VISAT™ system controller. The function of each component can be subdivided into primary and secondary tasks.

In terms of primary functions, the camera cluster provides up to 330-degree field of view with respect to the VISAT™ reference, which in most cases is the perspective center of one of the cameras. The position of this reference with respect to the existing control is determined by differential GPS, while the INS provides the camera orientation in three-dimensional space. The DMI provides the van traveling distance to triggers the cameras at constant intervals. The data-logging program VISAT™ Log allows for different camera configurations and different image recording distances or trigger the camera by time if necessary (both can be changed in real-time).

In terms of secondary functions, the camera cluster provides redundancy, i.e. more than two images of the same object. The GPS controls the INS error propagation. The INS, when used in positioning mode, bridges GPS outages, corrects GPS cycle slips, and gives precise interpolation between GPS fixes. The DMI data can be used to update the INS data if the GPS signal is blocked for periods longer than the INS bridging level required to fix the GPS integer ambiguities. The VISAT™ integrated navigational components can achieve accuracies of 0.1 - 0.3 m in urban or highway environment while operating at speeds of up to 110 km per hour. The combination of advanced technologies to achieve this accuracy level is what makes VISAT™ a very unique system.

VISAT™ Vision Component

In standard configuration, the VISAT™ Van includes 6 to 12 cameras offering an overlapped panoramic view of the area surveyed.   The cameras can be arranged in different configuration to provide all necessary viewing point for specific application.  The standard 6 cameras configuration offer a panorama to extract any road features like road signs, traffic lights, manholes, water valves, fire hydrant, and commercial signs.  The images are captured at programmable interval to create forward looking overlap of image sets.  The standard interval used is 5 meters so the same objects can be located in 3 or more overlapping images.  These high speed cameras can use a shutter speed from 60μs to 5 seconds.  The lens have remotely adjustable iris that are adjusted by the logging application that analyzes each images and set the iris to maximize the saturation level for best visual qualities.  The cameras are installed in a sealed enclosure with high quality and low distortion photogrammetric glass to protect them from the environment.

 VISAT™ System Controller

The heart of the system is the VISAT™ controller.  The controller is a powerful computer with high bandwidth bus taking full advantage of the 64 bits PCI-X interfaces for high traffic application. Several subcomponents are installed in the controller: a multi-channel real-time clock board (RTC) that registers synchronization information from all the sensors for a tight integration of the data, a frame grabber that receives images from all the cameras at high rate for maximum flexibility of frame rates, dual channel RAID SCSI adapter capable of storing images as fast as they are received, a 32 channels analog output board to interface with the lens, and all the other normal components found in a personal computer.

The RTC has multiple synchronized channels to synchronize the information at high precision.  The RTC uses an onboard clock running at 100 KHz to precisely maintain all the information synchronized.  It is also used to trigger the cameras on one channel following the configuration selected in VISAT™ Log, either distance-based using the information received from the DMI to trigger the cameras at fixed intervals, or time-based to trigger the cameras at a predefined rate.

The storage capacity of the controller is enough to store between 150km to 600km of images depending on the number of cameras and the storage options selected. The power supply control panel provides the DC power to all the sensors that can be selectively be powered on depending of the type of survey or optional sensors installed.  Bright lighted switch indicates which device is on and if the fuse is still intact to accelerate the troubleshooting of hardware failures.  

VISAT™ Log VISAT™ Log is the brain of the system which controls the operations of the survey and guides the survey crew to achieve the optimal outcome from the system.  Each sensor and device is an autonomous multithreaded component-based server that is controlled and coordinated by VISAT™ Log rich GUI main application. VISAT™ Log is not just a common passive data logger that save data coming from the sensors but rather take an active role in the process of creating georeferenced information to maximize the productivity and quality of the end results.  One example of such function is the Navigation Monitor which analyzes in real-time the incoming data of the navigation sensors and makes an assessment of the state and quality of the data, then provides visual indicators and recommendations to the operator. All the data logged during a survey are logged in its native format without any filtering or conversion so that the data can be post-processed using the manufacturer’s application for the sensor or by using GeoPROC™ for a complete post-processing cycle of creating georeferenced images. The information displayed to the user is grouped together in a tabulated control that allows selecting a specific page of interest.  Device Page This page displays the running devices and for each of them a general health indicators which allow the user to review normal operation messages, warnings, and critical errors. Real-Time Clock Page This page displays the states of all the active clocks and counters along with the DMI velocity.  Map Page This page displays the trace of the vehicle and the areas with images, the positions of static periods, and the location of the Master Station.  All this information is overlaid on top of a virtual road map that can be zoomed in and out to any scale. It maintains the current location of the vehicle visible to the operator at all time.  The map coverage includes all streets, road and highways in North America and Western Europe. Navigation Page This page displays the GPS position, GPS satellite constellation, and the INS data. A navigation data histogram is displayed to provide a global representation of the data.  Camera Views Page This page displays in real-time the images being captured to verify the quality of the images and to make sure the glass in front of the cameras are not obstructed by dirt or a bug.

Auto-Iris Page

This page displays the image histogram of each camera in real-time. The auto-iris controls assess the saturation level of the images and automatically adjust the iris to maximize their visual qualities.

Camera Devices Page

This page displays the actual state of the camera devices.

Image Queues Page

This page displays the 4 components that handle the images: the Raw Image Queue that receives the images from the cameras and store them on the RAID, the Processing Image Queue that streams the image to the Image Processing Engine then save the image on the removable disk, the Image Processing Engine that converts, adjusts the white-balance, sharpens, and compress’ the images, and finally the CD/DVD Burning Engine that automatically burns on the fly the image files that are splitted in media size (CD 650MB, DVD 4.7GB or 9.4GB) for easier handling.  All these components work in conjunction and are totally automated without any user interactions.

The Control Side Bar

The control side bar is located on the left pane of the application and contains the indicators of the Survey Monitor and the controls to select the trigger mode, enabling/disabling saving the images, and the control for the saturation levels that is used by the auto-iris module.

Copytight © AMS Inc. 2006
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