Point of Beginning


December 8, 2008

Posted By Paul Montero on 12/6/2008 at 1:59 PM

Good afternoon,

Say your task is to assemble data for a GIS (Geographic Information System) comprising an entire town. Geodetic control is all NAD29 (horizontal) and NAVD88 (vertical) for monuments in the town’s area.

Published values for all of the horizontal control monuments are in NAD29 U.S. Survey feet only. There are approximately twenty (20) horizontal 2nd and 3rd order monuments in the town. Published values for all of the vertical control monuments are in NAVD 88 meters only. There are approximately forty (40) 1st and 2nd order vertical control monuments in the town.

Information available from other sources include digital rectified aerial photographs, digitized topographic maps, wetland delineations and other essential information are published in NAD83 meters. How do you proceed? Do you…

A) Convert the values of the NAD29 horizontal control to meters.

B) Make new observations of the NAD29 monuments in meters.

C) Use the NAD29 datum and recalculate the bench marks to U.S. feet.

D) Other suggestions.


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