Chapter A. Introduction
Geodesy Is...
According to the Geodetic Glossary, geodesy is:
- The science concerned with determining the size and shape of the Earth.
- The science that locates positions on the Earth and determines the Earth's gravity field.
- The branch of surveying in which the curvature of the Earth must be taken into account when determining directions and distances.
That covers a lot of territory. The Glossary subdivides geodesy into eight general specializations or applications:
- astronomical
- geometric
- gravimetric
- intrinsic
- marine
- physical
- satellite
- three-dimensional
There is quite a bit of overlap because fundamental concepts are the same for each specialization.
The science of geodesy has evolved since the last edition of the Glossary (2001). Instrumentation and measurement technology have become more sophisticated causing even more overlap between specializations so as to totally blur division lines.
Prior to the common use of digital total stations (c1980s) and GPS receivers (c2000s), geodesy was strictly for geodesists. Once the everyday surveyor was able to measure distances that stretched the limits of plane surveying, geodesy became more mainstream. Until NAD 83 (covered in a later chapter) and GPS came along, surveyors only dealt with a single vertical distance: elevation. Technology required understanding what a geoid is, ellipsoidal heights, geoid heights, etc. GPS alone has exposed surveyors to more geodesy in the last 20 years than the previous 200.
The surveying profession is in the midst of a major positional reference framework paradigm shift. Horizontal and vertical surveys were once separate operations with procedural requirements often at odds with each other. Each had its own reference datum, updated as technology and measurements evolved. The move to 3D measuring systems requires a unified reference datum currently (2024) under development by the NGS. Along with that will come new coordinate systems including Low Distortion Projections.
This Topic merely touches on geodesy to provide a general framework. The NGS has a huge library of published materials in pdf form, live and archived presentations, and other educational resources. Visit their website at https://www.ngs.noaa.gov and select the Science & Education menu item.