Technical data

Introduction 1

Introduction

Although difficult to believe, it has been nearly 20 years since precise positioning

using the Global Positioning System (GPS) was demonstrated. In a relatively

short time, this capability was put to commercial use with the introduction of the

Macrometer V-1000 GPS receiver. Although the Macrometer was unwieldy,

temperamental, and very expensive ($150,000 each), its ability to geodetically

position points at an accuracy of 1-2 parts-per-million of point separation (1mm

per 1 kilometer), without the benefit of line-of-sight between the points, was a

tremendous asset. This was the birth of surveying with GPS.

From its beginning in the early 1980s to the mid 1990s, GPS surveying went

through a tremendous evolution. Equipment become much more affordable,

reliable, and manageable in size and weight. But through this entire period, two

important characteristics remained the same; accuracy and the surveying method

used to achieve this accuracy. The method was post-process GPS surveying.

With post-process GPS surveying, data is collected and later processed on a

computer to produce the final results, i.e. positions of all points surveyed. This

method can be equated to using a conventional theodolite and EDM to collect a

sequence of angles and distances between points, later computing the

coordinates of the surveyed points.

Until the mid 1990s, post-process was the only method available to determine

survey-grade positions using GPS. A new method was then introduced call Real-

Time Kinematic (RTK). With the RTK method, point positions are determined

immediately during data collection. This method can be equated to using a total

station to collect a sequence of angles and distances between points, with the

total station computing the coordinates of these points as the data is collected.

RTK GPS surveying has a number of advantages. The results of your survey are

known immediately. Also, with the ability to determine your position in real-time

comes the ability to stakeout. Balancing the advantages of RTK are some

disadvantages. RTK-enabled GPS systems are more expensive, in some cases

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