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LINK
EPSG website
Here, for example is the conversion of a point at 30 degrees North latitude and 70 degrees West Longitude from NAD 27 to NAD 83.
Latitude
Longitude
NAD 27 datum values: NAD 83 datum values:
30 00 0.00000 30 00 1.15126 1.15126 (secs) 35.450 (meters)
70 00 0.00000 69 59 57.30532 -2.69468(secs) -72.222(meters)
NAD 83 - NAD 27 shift values:
Magnitude of total shift:
80.453(meters)
Points to Ponder
The most important lesson from this is that conversions from one map system to another are complex and require specialist knowledge and accurate input parameters. Mistakes in this area may be undetectable on site and entire databases have been known to be wrongly converted resulting in very expensive consequences. This is certainly not a job for a casual spreadsheet.
The main consideration here is that it is essential that when positioning a well, the geoscientists, the operator and the drilling contractor are all working on the same map system on the same datum as the shift in position can be enormous and frequently far bigger than the well target tolerance.
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