A Puzzle from the Age of the EDM and Theodolite

Kent McMillan · 2011-03-08T04:55:51Z

Here's a puzzle of somewhat more modern origin. On one day in August of 1981, a surveyor set up a one-second theodolite and AGA EDM on the above 60d nail control point that he had connected by traverse to various original survey corners that he used to construct the lines and corners of one particular survey that had originally been located entirely on paper as described in field notes filed at the Texas General Land Office in 1886. His field book indicates that he set up on this control point and proceeded to stake out four corners on the West line of the originally protracted survey as computed by him, marking each with a 1/2-inch rebar with plastic cap imprinted with his professional identification and building a rock mound around eachNaturally, he measured horizontal angles and slope distances with zenith angles to the markers he set out. The reductions to horizontal in his field book check arithmetically. So, his field record was that from this nail he set rod and cap markers in rock mounds at these astronomic azimuths and horizontal surface distances:100...175°56'31".Az...2887.79 ft.64....333°38'51".Az....672.46 ft.68....352°49'18".Az...2388.84 ft.Three 1/2-inch rebars in rock mounds are recovered, none of which have the plastic cap remaining on them and are found to lie at these grid azimuths and horizontal distances from this nail as computed from GPS vectors.100...178°38'31".Az...2387.98 ft.64....336°21'16".Az....672.50 ft.68....355°31'04".Az...2388.91 ft.Yes, the distance to iron rod 100 is definitely 499.81 ft. shorter than the distance that was recorded clearly and unambiguously in the field book of the surveyor in 1981.At the nail, the relationship between grid azimuth of the applicable zone of the Texas Coordinate System and geodetic azimuth : Geodetic Az. = Grid Az. - 2°34'29"The difference between Geodetic Az. and Astronomic Az. at the nail is only about 0°00'04".There is no record of a recovery of any marker at the position where the 1981 surveyor's records plainly show that he set one.So, with the available information mentioned above in hand, how might a surveyor go about proving or disproving that the Rod and Rock Mound No. 100, 499.81 ft. from the position in which the surveyor's record notes that he set a marker, is actually what is left of the 1981 surveyor's rod and cap or not?(PS: It's true that the rod and rock mound in question is 13.4 ft. South of an old pasture fence, but this is Texas and that fence is a casual fence with no relationship to any boundary.)

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Kent, I don't practice in Texas. But my off the cuff answer is to call it a blunder. Set the correct corner, and go home.

I mean, if a doctor makes a blunder this big, and his patient is still alive, he would want it to be corrected, if he cared about his patient!

Posted : October 18, 2012 6:58 am

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A Puzzle from the Age of the EDM and Theodolite

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