Abstract
Since the 1990s, the integration of GPS and GIS has become more and more popular and an industry standard in the GIS community worldwide. The increasing availability and affordability of mobile GIS and GPS, along with greater data accuracy and interoperability, will only ensure steady growth of this practice in the future. This chapter provides a brief background of GPS technology and its use in GIS, and then elaborates on the integration techniques of both technologies within their limitations. It also highlights data processing, transfer, and maintenance issues and future trends of this integration.
TopBackground
Need for GPS Data in GIS
When people try to find out where on earth they are located, they rely on either absolute coordinates with latitude and longitude information or relative coordinates where location information is expressed with the help of another location (Kennedy, 2002). GIS maps can be created or corrected from the features entered in the field using a GPS receiver (Maantay and Ziegler, 2006). Thus people can know their actual positions on earth and then compare their locations in relation to other objects represented in a GIS map (Thurston et. al, 2003; Kennedy, 2002).
GIS uses mainly two types of datasets: (a) primary, which is created by the user; and (b) secondary, which is collected or purchased from somewhere else. In GIS, primary data can be created by drawing any feature based on given dimensions, by digitizing ortho-photos, and by analyzing survey, remote sensing, and GPS data. Using GPS, primary data can be collected accurately and quickly with a common reference system without any drawing or digitizing operation. Once the primary data is created, it can be distributed to others and be used as secondary data. Before using GPS as a primary data collection tool for GIS, the users need to understand the GPS technology and its limitations.
Key Terms in this Chapter
Datum: The reference specifications of a measurement system, usually a system of coordinate positions on a surface or heights above or below a surface.
DGPS: The Differential GPS (DGPS) is used to correct GPS signal data errors, using two receivers, one stationary (placed at a precisely known geographic point) and one roving (carried by the surveyor). The stationary receiver sends differential correction signals to the roving one.
Coordinate System: A reference framework used to define the positions of points in space in either two or three dimensions.
GPS Segment: GPS consists of three segments: (i) space segment – the GPS satellites, (ii) user segment – the GPS handheld navigator, and (iii) ground control segment – the GPS monitoring stations.
Projection: A method requiring a systematic mathematical transformation by which the curved surface of the earth is portrayed on a flat surface.
WAAS: The Wide Area Augmentation System (WAAS) is a system that can increase the GPS signal data accuracy to 1 to 2 meters horizontally and 2 to 3 meters vertically.
Scale: The ratio between a distance or area on a map and the corresponding distance or area on the ground, commonly expressed as a fraction or ratio.