Pennsylvania Society of Land Surveyors Newsletter The
Pennsylvania Surveyor Summer 2017
A Land Surveyor’s Look at Geodesy and Datums
By: William Henning, PLS
Because the average age of Land Surveyors in the USA is around 57, many will remember their experience with creating a datum. That’s right –two hubs driven into the ground near the edge of the road and a PK nail smacked into a power pole. Your project datum was then, as a result of intensive computations, loaded into your field book, noting that your “origin” point was 5000.000 North and 10,000.000 East and the azimuth on your project “standard parallel” was 90° (quite coincidentally due east). Your vertical datum (in the North American Damfino datum), as a result of spherical harmonics, removal of free air anomalies and reduction of a Fourier series, was found to be exactly 100.00 feet on the PK nail. Well, good things don’t last forever. With the beginning of the Acronym System, containing GIS and GPS, everything needed to fit together (GIS) and the means to do it (GPS) became ubiquitous. Now the land surveyor entered into the cob-webbed realms of geodesy and geodetic datums. Suddenly the surveyor found out that an inverse between monuments with State Plane Coordinates Continued on Page 6
Inside... Cover Feature: Geodesy & Datums President’s Message...3 NSPS Report...4 NSPS Foundation ...5 Timeless Wisdom… 9 Sustaining Firms…12 The Snake...15 PLS Foundation Firearms Raffle...16 Member News & Events...19 Conference Venue Report… 20 On the Lighter Side...22