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INTEGRATING DIFFERENTIAL GPS WITH AN INERTIAL NAVIGATION SYSTEM (INS) 
AND CCD CAMERAS FOR A MOBILE GIS DATA COLLECTION SYSTEM 
El-Sheimy N. and K. P. Schwarz 
Department of Geomatics Engineering, The University of Calgary 
2500 University Drive, N. W. , Calgary, Alberta, Canada T2N 1N4 
ISPRS Commission II, WG II/1 
KEY WORDS: Highway survey system, Sensor integration, Geographical information system (GIS) , CCD cameras, Inertial 
navigation system , Differential Positioning with GPS. 
ABSTRACT 
The creation of a Geographic Information System (GIS) for road networks requires large amounts of data which currently are 
obtained by manually digitizing existing maps with some update from conventional photogrammetric and surveying 
techniques. In order to collect digital data faster, the use and integration of digital sensors is required which work in kinematic 
mode, i.e. from a moving vehicle. The University of Calgary has developed a precise mobile survey system for road inventory 
and general GIS applications. The system integrates a cluster of CCD cameras, a GPS receiver, and an Inertial Navigation 
System (INS), to automatically collect data in a road corridor at velocities of 50 - 60 km/h and to store this data in a GIS 
system format. The updated GPS/INS information is used to geometrically correct the images collected by the CCD cameras 
which record all details along the highway within a corridor of about 50 m. The shutters of the cameras and the output of the 
INS system are synchronized by the clock of the GPS receiver. 
In this paper an overview of the sensor integration and the mathematical transformations required to convert the image 
coordinates into 3-D coordinates will be given. Also, some data storage, merging and manipulation problems will be 
addressed. Special emphasis is given to the contribution of each subsystem to the overall error budget of the derived 3-D 
coordinates which have been assessed using test results recently obtained. 
1. INTRODUCTION 
During the last decade, the demand for GIS in management 
and design applications has greatly increased. The 
realization of a GIS in many application areas still suffers 
from data acquisition problems. To be of value to the user, a 
GIS must be updated regularly, so that the information in the 
data base correctly represents the real world. However, the 
acquisition of up-to-date GIS data by conventional survey 
techniques is prohibitive in cost and has therefore limited 
the applicability and usefulness of GIS to potential users. 
Described in this paper is an attempt to overcome this 
problem. 
A data acquisition system has been designed and 
implemented at The University of Calgary (U of C) that can 
be used to selectively update GIS data bases very quickly and 
inexpensively. The system integrates a cluster of Charged- 
Coupled-Devices (CCD) cameras, an Inertial Navigation 
System (INS), and satellite receivers of the Global 
Positioning System (GPS). Figure 1 shows the system in 
schematic form. The overall objective was the development 
of a precise mobile highway survey system that could be 
operated at a speed of 60 km per hour and achieve an accuracy 
of 0.3 m (RMS) with respect to the given control and a 
relative accuracy of 0.1 m (RMS) for points within a 50 m 
radius. This accuracy is required in all environments 
including inner cities, 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 transfer into a GIS system. The new system is 
named VISAT and derives its name from the fact that it 
utilizes Video images, an INS system, and the GPS Satellite 
system. For further details on the design of the VISAT 
system, see Schwarz et al (1993a) and El-Sheimy and 
Schwarz (1993); for the workstation design, see Li et al 
(1994). 
This paper gives an overview of the most important 
components of the VISAT system, discusses the underlying 
principle of extracting three dimensional (3-D) coordinates 
from the video images through the use of INS/GPS data, 
highlights some of the integration problems, and analyses 
results recently obtained in field and laboratory tests. 
2. SYSTEM CONCEPT AND FUNCTIONALITY 
The hardware component of the VISAT system consists of 
three sensor systems, two ASTECH PXII GPS receivers, a 
LTN 90-100 strapdown INS, and two COHU 4912 CCD 
cameras. 
The GPS is capable of providing very accurate position and 
velocity under ideal conditions. However, such conditions 
do not often exist. Independent GPS navigation requires at 
least four satellites. To reach the accuracy required for the 
VISAT system, it has to be used in differential mode, e.g. 
using double differencing techniques. The major drawback of 
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