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In order to perform precise positioning, it is necessary to
calibration the entire system. The camera geometry, the
lens distortions, the relative orientation parameters and the
offset between the stereo vision system and GPS/INS
system must be determined. The camera geometry may be
constant for long time, but the relative and rotation offsets
may change between the different missions. The entire
system calibration are divided into two parts. The first part
is the calculation of camera parameters using known
control points in a test-field, the second is the calculation
of the relative orientation and rotation offset based on the
coplanarity equation and constraints. In the second part,
the position and rotation parameters of an image pair is
used. No additional controls are required. This is well-
suited for the mobile mapping system.
Data from the GPSVision are converted into a format
directly acceptable for entry into a GIS. After the
information is analyzed, highway officials or utility
companies use it to support management decision making.
The GPSVision is an ideal platform for cost-efficient
multimedia collection of the spatially-referenced digital
data that is highly accurate, current, homogeneous and
consistent, and therefore, well-suited for the generation of
a land-based geographic information system.
2. System Configuration
The hardware component of the first generation of the
GPSVision consists of three major components: a Trimble
ProXL code-phase GPS receiver, a Liton LN-200 inertial
navigation system and two color CCD cameras. The
GPSVision is a very flexible system, many different types
of GPS receivers or cameras are also used in the
GPSVision system depending on the application
requirement, e.g. The Trimble SSI GPS receiver is used to
achieve the point accuracy for 10 to 20 cm. The other
important feature is its independence with the moving
platform, it is portable and can be mounted on different
vehicles. Fig. 1 shows the GPS receiver, the left camera
and the INS system which are inside the box.
Fig. 1 The GPS, INS and left camera of
the portable GPSVision system
À PC-computer provides for the overall control, storage,
display and operator interaction during the data
155
acquisition. It is constructed on a passive backplane
chassis and mounted in a rugged industrial chassis with a
single board CPU. The single board CPU is a 486
DX/66MHz PC executing a standard multi-tasking
operating system. The backplane also has an INS interface
consisting of a SDCC digital interface, Built-In-Test (BIT)
board, and a timing interface board. In addition to the
boards, the chassis will also contain a solid state or
standard storage device and a boot device.
The Built-In-Test Diagnostic System provides hardware
status of all sub-systems to the operator and warns of
pending maintenance action or failure. The BIT consists of
a digital I/0, a digital to analog converter and an analog to
digital converter board for monitoring each subsystem
The GPS unit provides the system computer with GPS
timing, distance measurements, satellite data and satellite
status information. The solid state INS provides changes
in direction and speed data. The GPS time is unique and
all collected data are correlated on the GPS time. All data
are stored in a binary format and used in post-processing
software.
The vision system consists of two high resolution color
CCD cameras that provide overlapping stereo images, two
digital frame buffers and an optical disc recorder. The
cameras are progressive scan CCD units with auto IRIS
wide angle lenses. The image capture of stereo image pairs
is user configurable by distance or time. For example, a
stereo pair of images can be captured at an interval of 16
meters.
The operator interface consists of a laptop computer
running Microsoft DOS / Windows. The laptop is
connected to the PC-computer through a network device.
It acts as a terminal for control and a digital storage
device.
3. Positioning
The Positioning procedure of the GPSVision consist of
two steps: determining the position and rotation of the
image pair in a global coordinate system and the
positioning of an object from an geo-referenced image
pair. The first step is to combine the GPS and INS data
using the kalman filter method and determine the 6
necessary parameters (three position parameters and three
rotation parameters) of the GPSVision at the time when
an image pair is taken. The second step determines the
three-dimensional coordinate of an object by a
photogrammetric triangulation and transfers it into the
global coordinate system.
In the GPSVision system, the GPS receiver, INS and two
CCD cameras are mounted on a stationary platform. Their
relative position is stable during a survey. Once the camera
parameters and the relative orientation parameters are
known, a three-dimensional local coordinate of an object
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
