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Return to The Elements of Geodesy: The Vertical Datum

Similar to the survey markers used to identify positions in the horizontal datum, round brass plates mark positions in the vertical datum. The markers are embedded in concrete or bedrock to maintain their positions and, therefore, the integrity of the geodetic control point. Here we see how the position of a vertical survey marker in Louisiana has been upset due to significant subsidence (sinking) of the surrounding area.


Brass monument in the midst of a subsidence area.

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