Full text: Systems for data processing, anaylsis and representation

M. Elizabeth Cannon 
Department of Geomatics Engineering, The University of Calgary, 
2500 University Drive N.W., Calgary, Alberta, T3H 1Z2, Canada 
KEY WORDS: GPS, GIS, surveying, georeferencing, receiver, static, kinematic 
The use of GPS for georeferencing has entered a new age with the operational capability of GPS system as 
well the developments in GPS receiver technology and processing strategies. The current status of GPS 
methods and accuracies are reviewed in the context of GIS applications. Trends in GPS hardware are also 
presented. Several applications of GPS for the acquisition of spatially-related data are discussed. These 
include applications in the agricultural sector for salinity mapping and variable fertilizer spreading. 
Other applications in urban environments are also presented where shading problems may limit the 
achievable accuracy and availability of GPS. The paper concludes with a discussion of the trend in GPS 
processing developments, especially high precision real-time positioning, and its impact in the GIS field. 
The Global Positioning System (GPS) has already 
made a major impact into the fields of surveying 
and georeferencing. With the completion of the 
satellite constellation, the reduction in receiver 
costs, as well as improvements in processing 
algorithms and related software, the growth in 
applications is expected to continue. Most recently, 
the GIS field is embracing the use of GPS for 
moving platform applications, the so-called 
kinematic approach where large amounts of data 
can be collected in a cost-effective manner. The 
following papers focuses on the current state of the 
GPS system, the options for receiver hardware 
selection, the numerous modes of data collection as 
well as a cross-section of kinematic GPS 
applications for the land, marine and airborne 
GPS is entering a new era now that the system is 
nearing completion and moving to the operational 
phase. There are currently 26 satellites in orbit of 
Which 3 are prototype Block I. Under this 
constellation, the geometry is effectively 
consistent throughout most of the day as evidenced 
by the Position Dilution of Precision (PDOP) 
Which is given in Figure 1 for satellites in view at 
Calgary in March, 1994. The PDOP is a figure of 
merit for the satellite geometry and a value below 
three can be considered good. Since the satellite 
Coverage is generally below three for most of the 
day, detailed mission planning is not as important 
as in the past except when satellites become 
unhealthy which may cause outages. Another 
Block II satellite is expected to become operational 
in mid-March, 1994 which will further enhance 
the current coverage. 
A er 
d Al 
mann nt — 
0 4 8 12 16 20 24 
Time (Hr) 
Fig. 1: Position Dilution of Precision (PDOP) for 
Calgary in March, 1994 
With the availability of continuous GPS coverage, 
the use of the system for a wide range of 
applications is increasing at high rate. In order to 
meet these range of applications, GPS receiver 
manufacturers currently offer a wide range of 
products that vary in size, cost, performance and 
capabilities. Table 1 gives a list of some of major 
classes of GPS receivers. The first is the 
Coarse/Acquisition (C/A) code engine which is a 
GPS receiver on a circuit board having dimensions 

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