Underground mark only

[Bill93]

GH55 and I were in our home town last weekend for the annual celebration, and as we have done in some prior years we did a team hunt. This time it was for the triangulation station LE0530 that bears the name of the town. Not really old, just 1928, but the name made it more interesting.

 

I thought I'd post it because of some recent discussion about triangulation stations where the surface mark was gone.

 

I had previously scouted out the area to find RM3, and the AZ mark that is no longer directly visible, but had failed (in the rain) to measure carefully enough to find RM4. The land owner told us the chunk of concrete at the corner was the station (disk is gone), which he had plowed out many years ago (maybe due to the ridge getting flattened by farming and regrading with road construction).

It seemed that the underground mark should still be there, originally 5 ft down but now enough shallower that the surface mark had been within plow depth. Still, it was going to be at a depth the metal detector would not work, the ground would be very hard to probe to sufficient depth, and we didn't want to dig a wide hole.

 

So, expecting that we only had RM3 to work with, I calculated angles from the town water tank which is an intersection station, and loaded up my GTS-2B semi-total station (i.e. transit).

 

Gary actually found RM4 right away, so we could have found the spot by measuring from the two RMs. Not sure how accurately with a cloth tape in the wind. I wanted to go ahead and play with the total station, so I set up on RM3 and turned the angle to the tri-station. We set a reflector on that line and moved it to get the required distance, and marked the spot to dig.

The disk was actually 2 ft 5 inches down and well within the post hole we dug.

We had a lot of trouble cleaning it off while working at arm's length. They probably used some kind of tarry material to separate the underground mark and the concrete of the surface mark, and it took a lot of scraping with a wooden stake to get off. We could have done a better job for the picture, but stopped when we could clearly read the stamping.

 

The owner and his son were interested enough to drive out and look. He said "yup, that's about where I hit it."

 

I took some measurements of angle and distance between the station and RM's but must not have fussed enough with centering the instrument and positioning the freflector's plumb line (in the breeze). I thought I would be able to check within 1/4 inch of the box score values but the measurements came out 1/2 to 1 1/2 inch off, not consistent enough to say one of the disks was off.

Edited August 10, 2009 by Bill93

[Difficult Run]

Great story Bill,

 

One of the best recoveries I've read in recent memory!

 

~ Mitch ~

[topflitejr1]

Awesome! persistance payed off! I like that an Intersection Station was used to help find the Mark. Take that you IS haters!