You are in the Lesson 5 online content now. (That forum can be accessed at any time by going to the GEOG 862 course in Canvas and then looking inside the Lesson 5 module.) To participate in the discussion, please go to the Lesson 5 Discussion Forum in Canvas.
You can also navigate the lecture material via the links in the Lessons menu. Click on the links at the bottom of the page to continue to the next page, to return to the previous page, or to go to the top of the lesson. Read the lecture material for this lesson. Read "A Few Pertinent Ideas about Geodetic Datums for GPS" in Chapter 5 pages 129 to 141 in GPS for Land Surveyors The Overview page is previous to this page, and you are on the Checklist page right now. You may find it useful to print this page out first so that you can follow along with the directions. (See the Calendar in Canvas for specific due dates.) To finish this lesson, you must complete the activities listed below.
#Definition of datum free
(To access the forum, return to Canvas and navigate to the Lesson 5 Discussion Forum in the Lesson 5 module.) While you are there, feel free to post your own responses if you, too, are able to help out a classmate. If you have any questions now or at any point during this week, please feel free to post them to the Lesson 5 Discussion Forum. define the elements of a geodetic datum.recognize the structure of some geodetic coordinate systems.describe a few pertinent ideas about geodetic datums.demonstrate understanding of the basics of geodetic coordinates.ObjectivesĪt the successful completion of this lesson, students should be able to: The next lesson concerns some of the elements of the systems we inevitably use to accommodate the vagaries of assigning coordinates to the results of an earth-centered-earth-fixed positioning system based on signals from satellites. Even with electronic tools that widen the scope and increase the precision of the data, perfection is nowhere in sight. The attachment of elevations to such horizontal coordinates somewhat acknowledges the topographic irregularity of the earth, but the whole system is always undone by its inherent inaccuracy as the area grow large. Even though we have always known that this assumption of a flat earth is fundamentally unrealistic, it provided, and continues to provide, an adequate arrangement for small areas. This rectangular system is used to describe measured positions by ordered pairs, usually expressed in northings and eastings, or y- and x - coordinates.
Plane surveying has traditionally relied on an imaginary flat reference surface, or reference frame (datum), with Cartesian axes. Each projection serves a particular application well, but none of them can represent the Earth without distortion.Īs the technology of measurement has improved, the pressure for greater exactness in the definition of the Earth's shape has increased. There have been a whole variety of map projections developed over the centuries that rely on mathematical relationships between positions on the Earth's surface and points on the map. The dilemma is illustrated by the ancient struggle to represent its curved surface on flat maps. Despite the certainty of the physical surface of the Earth, it remains notoriously difficult to define in mathematical terms.
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