Data acquisition

VISATTM has been developed over a period of more than twenty years of active R&D and testing resulting in an extremely positionally precise state-of-the-technology "virtual surveying" mobile (i.e. street-level) data and image acquisition and analysis system.

VISATTM has specifically been developed to provide an answer and a solution to the increasing demand for up-to-date 3D GIS.

VISATTM provides a task-oriented implementation of mapping concepts. Surveying by VISATTM consists of three steps, which are essentially the same as for any mobile mapping system:

  • Data acquisition;
  • Georeferencing of the images using data from the navigation sensors (GPS and SINS);
  • Positioning of objects in a mapping frame using a photogrammetric workstation and two or more georeferenced images

The VISATTM "virtual surveying" system consists of a number of carefully calibrated and integrated modules:

  • Mobile mapping van (MMV) / sensor platform (VISATTM Van)
  • Real-Time Multi-Sensor Data acquisition software (VISATTM Log)
  • Data management, post-processing and distribution software (VISATTM GeoImages Server)
  • Feature extraction, measuring, and analysis software (VISATTM Station)
  • Panoramic street views and virtual street visits (VISATTM Viewer)
  • Automated Road Vector Extraction Engine (VISATTM ARVEE)

VAN

The core hardware components of the VISATTM van are a Strap down Inertial Navigation System (SINS), a dualfrequency GPS receiver, and a cluster of digital color cameras. The primary purposes of these components are - the GPS provides the position of the van, the SINS provides the orientation of the van, and the cameras are used for relative positioning from the van. These components, however, also have important secondary functions.

For the GPS, these secondary tasks include controlling the long-term error growth of the SINS through the GPS/SINS Kalman filter and providing the precise timing base for all data streams.
The secondary tasks of the SINS stem from its ability to be used as a position sensor in addition to an orientation sensor; consequently, these tasks include bridging GPS signal outages, detecting and correcting GPS cycle slips, and precise interpolation between GPS positions.

The latter task - interpolation between GPS positions - is possible because the SINS provide data at 200 Hz, while the GPS positions and velocities are only available at 1-2 Hz.

In addition to the GPS, SINS, and cameras, the VISATTM system also integrates a Distance Measuring Instrument (DMI). The pick-up from the DMI is used to trigger the acquisition of the images from the cameras at constant distance intervals defined by the user and provides longitudinal velocity for helping to georeference the solution.

Currently, the VISATTM imaging component consists of 6 to 12 progressive color digital cameras (2048 x 2048 pixels) which provide a 330 to 360° field of view.

The images are captured at high sampling rates and can be controlled by either time or traveled distance. Images are captured while the van is moving at the highway posted speed (up to 120 km/h). Essentially, all navigation and mapping data streams are synchronized to a common time frame using a high frequency synchronized multi-channel clock. VISATTM has an efficient and robust data logging module which enables the collection of the data with minimum time delay.

The VISATTM logging system also has an expert module for real-time quality control, which communicates with the system's operator and provides useful information such as length of the survey, distance to master station, directions to specific routes, etc.