Coordinates

Jan Van Sickle, P.L.S.

Course Outline

This online course discusses the processes and procedures involved in handling coordinates in surveying, mapping and GIS. Since most, if not all, of these processes and procedures are now computerized the need for understanding them is not always immediately apparent. However, without that understanding the user can be led astray, quickly and disastrously by the same computer programs that make coordinate manipulation so automatic. Incorrect coordinates can, at a stroke, dramatically erode confidence in an entire body of work.

The development of GPS and the almost universal use of this utility also brings and understanding of coordinates to the fore. When GPS is used as a measurement system it is not possible to avoid geodetic considerations.

This course not only provides the foundation of basic geodesy, it also explains how those ideas are pertinent to everyday work. There are no complex mathematics in this course. The relationships that are incorporated for the illustration of the ideas discussed. Those ideas, those concepts, are the heart of the course.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

• Immediately recognize some of the most common problems with coordinates;
• Realize the significant differences between North American Datum 1927 (NAD27) and North American Datum 1983 (NAD83);
• Know the distinctions between State Plane Coordinates 1927 (SPCS27) and State Plane Coordinates 1983 (SPCS83);
• Learn the procedures for converting heights from GPS (ellipsoidal heights) to orthometric heights;
• Be aware of the four processes commonly used in coordinate transformation;
• Recognize three different sorts of Geographic coordinates (Latitude and Longitude) and their significance;
• Understand the Geoid model at the foundation of orthometric heights;
• Be acquainted with the decisions that led to the establishment of the North American Datum 1983 (NAD83) and the pertinence to everyday work;
• Know the underlying fundamentals of Geographic coordinates (Latitude and Longitude);
• See the limitations of the concept of Mean Sea Level;
• Understand coordinates of the International Terrestrial Reference Frame (ITRF) and their place in today's work;
• Be aware of the different processes used to attach Reference Ellipsoids to the real Earth in the past and today;
• Be conversant with the procedures for realizing Geodetic Datums;
• Be familiar with the decisions that led to the establishment of the North American Vertical Datum 1988 (NAVD83) and the pertinence to everyday work;
• Recognize the implications of today's geocentric datums;
• Be informed about map projections and their place in State Plane Coordinates systems;
• Understand Dynamic heights;
• Learn the distinctions between Geodetic lengths and Grid lengths in State Pane Coordinate systems and UTM;
• See the process of converting Geodetic Azimuths to Grid Azimuths and vice versa;
• Have knowledge of the procedures used to build Grid, Scale and Combined factors for conversion in State Plane Coordinate systems;
• Be aware of some free online sources for coordinate conversions;
• Be well-versed in procedures used to construct Reference Ellipsoids;
• Understand the Deflection of the Vertical and its pertinence;
• Be knowledgeable in procedures used by the International Earth Rotation Service (IERS) for the maintenance of ECEF systems; and
• Recognize Cartesian and Polar coordinates and the differences between them.
  
  

Intended Audience

This course is intended for land surveyors, GIS professionals and engineers.

Benefit to Attendees

Attendee of this course will be able to handle coordinates with confidence, recognize bad data quickly and know what to do about it when it occurs.

Course Introduction

Coordinates are not nearly as stable as they sometimes appear. Coordinates are not certain, even if their figures are precise. A latitude of 40º 25' 33.504"N with a longitude of 108º 45' 55.378"W appears to be an accurate, unique coordinate, but it could correctly apply to more than one place. This very latitude and longitude once pinpointed a control point known as Youghall. Youghall is a bronze disk cemented into a drill hole in an outcropping of bedrock on Tanks Peak in the Colorado Rocky Mountains, its not going anywhere. But its coordinates have not been nearly as immovable as the monument. In 1937 the United States Coast and Geodetic Survey set Youghall at latitude 40º 25' 33.504"N and longitude 108º 45' 55.378"W. You might think that was that, but in November of 1997 Youghall suddenly got a new coordinate, 40º 25' 33.39258" N and 108º 45' 57.78374" W. That's more than 56 meters, 185 feet, west and 3 meters, 11 feet, south of where it started. But Youghall hadn't actually moved at all. Its elevation changed too. It was 2658.2 meters in 1937. It is 2659.6 meters today. It rose 4 ½ feet.

Of course it did no such thing, the station is right where it has always been, its datum changed. The 1937 latitude and longitude for Youghall was based on the North American Datum 1927 (NAD27). Sixty years later, in 1997 the basis of the coordinate of Youghall became the North American Datum 1983 (NAD83). How and why did that happen?

Course Content

The link to the course content is as follows:

Coordinates (PDF file 2.8 MB)

You need to open or download the above document to study this course.

Course Summary

Computers are excellent at doing exactly what they are told to do. They are very good at repetition. They are ideal coordinate generation and manipulation tools, but they are very bad at interpretation. People, on the other hand, are excellent indeed at interpretation of coordinate data, that is if we have the information to understand what we are interpreting. This course was about providing some of that information.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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