Abstract

Orthometric Heighting with GPS
Track: Training
Authors: Thomas Meyer

In today's world, GPS is becoming more and more commonly used for vertical control. GPS heighting can be attractive from a cost perspective because it offers the possibility of reducing or eliminating the need for leveling runs and trig-heighting, which are very costly. Although GPS is not a panacea, the prospect of establishing high-quality vertical control in a remote site without running levels to distant bench marks is very attractive.

Unfortunately, traditional training in leveling does not adequately prepare a surveyor to perform GPS heighting because the two techniques are nearly completely different. For example, different instruments are used for each technique; the concept of a leveling route does not exist in GPS heighting; they have different error budgets; they reference different vertical datums; and they are even based on different conceptualizations of height itself. Therefore, the goal of this seminar to try to bring these worlds together; to help prepare participants to perform survey-quality GPS heighting.

This seminar presents both conceptual and practical material to meet this goal. The participant will learn concepts such as reference ellipsoids, vertical datums, mean sea level, level surfaces and the geoid, gravity and potential, and orthometric vs. geometric vs. ellipsoid heights. From these concepts come applications such as why some reference ellipsoids are suitable as vertical datums while others are not; what is a GPS really doing when used for heights, how to integrate its measurements with those of a spirit level, and what is an orthometric correction. Finally, a section on practical aspects of GPS heighting will be covered based on suggested practices given by the National Geodetic Survey in light of its height modernization program. This section will consider network design, the role and application of geoid models, the integration of leveled heights with GPS-determined heights, and end with an extensive, real-world example survey.