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Points to Ponder
The most important lesson from all this is that a latitude and longitude coordinate do not uniquely define a point in space unless the datum name is included as part of the description! Please also note that knowing the name of the ellipsoid is not enough. An ellipsoid is a shape in space and the same ellipsoid can be attached to the Earth at an infinite number of places. Each time an ellipsoid is attached to another place it represents a different datum. Particular examples occur in West Africa, where many countries use the Clarke 1880 ellipsoid but set up as a different astro- geodetic datum in each case, and in Brazil where three datums use the International ellipsoid of 1924.
Ten Things to Remember about Geodesy and References:
1. Latitude and Longitude are not unique unless qualified with a Datum name. 2. Heights/Elevations are not unique unless qualified with an height/elevation reference. 3. Units are not unique unless qualified with unit reference. 4. Orientations are not unique unless qualified with a heading reference. 5. Most field data of all types are acquired in WGS 84 using GPS. 6. Every time data are sent somewhere there is a chance someone will misinterpret the references. 7. Most datasets have an incomplete set of metadata describing the references. 8. All software applications are not created equal with respect to tracking and maintaining metadata. 9. Data can be obtained by anyone from anywhere – h do sn’ m k gh ! 10. Most people do not understand geodesy - if you are in doubt – check with someone who knows!
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