No Formulas Needed

摘要

In June 2015, CRS Press released the 4th edition of GPS for Surveyors written by Jan van Sickle. The 2nd edition was published in 2001 and the 3rd in 2008. Apparently the revision cycle is seven years. The 4th edition starts with a chapter on the main features of the GPS signals which are broadcast in the microwave part of the electromagnetic spectrum. Page 1 gets straight to the point: "Millions of GPS receivers may monitor the satellite's signals without danger of overburdening the system." This distinct pro is accompanied by the burden that GPS positioning necessitates the gathering of abundant signals and advanced processing. After understanding the signals and how pseudoranges, ranges and positions are related to phases and codes, Chapter 2 clarifies that all this know-how is of little value when the surveyor does not grasp the bunch of errors introduced by satellite orbital biases, clock offsets, ionospheric and tropospheric delays, multipath and receiver noise and how to manage and (partly) eliminate these. Surveyors may complain that new technologies enable laymen to do the job, thus jeopardising their profession, but Chapter 2 elucidates that the profession is shaped not by technology but rather by knowledge and skills.