GPS and WGS84 _ 1

28.10.2004

Submission:

Concerning the matter, in my opinion, the ICAO Doc 9674 - WGS-84 Manual (second edition 2002) is a very good guidance material. The Chapter 4 of the above mentioned document is entitled "A guide to obtain WGS-84 co-ordinates" and gives the steps necessary, depending on the existence and the quality of aeronautical data, to get these co-ordinates. There are described different scenarios based on the question : Are co-ordinates in a local reference system (in the required accuracy) available or not ? If not (Scenario 2 - paragraphs 4.3.1 and 2) are given the "best technique(s) for new field survey depending of the areas to be surveyed (small, large or obstructed). In conclusion, an answer for you would be in the Note at the end of para., 4.3.2:

"Note: There is no doubt that a complete resurvey of the point using differential GPS satellite surveying techniques (relative to a known station with WGS-84 co-ordinates) is the most accurate approach for determining precise WGS-84 co-ordinates "

Of course, it's also a matter of resources and costs (!)

Sorin Onitiu - FIDesign - Jeppesen