Jim Cain and John Stigant of the Americas Petroleum Survey Group held a half day workshop on Geodetics, Datums and Projections as applied to the oil industry. Cain laid down the basics of geodetics for geodetically-naïve end users or programmers. Cain’s clear message is ‘latitude and longitude are not a unique representation of a point on the earth’s surface—but vary according to the geographical coordinate reference system used’.
Lost in space!
Or, putting it in plain English, ‘given latitude and longitude, you do not know where you are’. Errors of the order of a hundred meters or more can come from misunderstandings of geodetic datum. Other pitfalls await the unwary when 3D data is projected onto a 2D map. Stigant ran through the plethora of map projections available—with case histories of projection disasters. ‘People get it wrong all the time—there is a constant need for education, you should always re-check software to make sure that scale factor and declination have been handled properly.’
Beware of software that allows ‘unknown’ datum—a geodetic anathema. Wells pose a delicate problem—a deviation survey records a vast amount of metadata which may or may not be available in a trade context. One recurrent problem is the over zealous re-application of a correction—stressing the need for audit trails.
Pipelines pose another type of mapping problem—accurate knowledge of ellipsoid height and height above mean sea level is required to avoid pumping uphill at unexpected pressure! Another scare story involved the building of a production facility accidentally located on a neighboring property— resulting in a $12 million windfall for the owner! Stigant advises checking and double checking your survey data. If in doubt – get help! Done well, geodetics can be a low cost, high competitive advantage activity. Done badly, they have huge risk potential. The APSG (www.apsg.info) is ready to give this presentation to corporations on request.
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