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Wintertime

What Do These Sidewalk Markings Mean?

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Okay, I cheated a bit on the topic title and description. ;-) I snuck in two topics, but they're both related to the same benchmark.

 

I went looking for HT1213 yesterday. I found the transmission tower, but couldn't get near it due to construction fencing--the same construction that now puts the benchmark in a parking area for cement trucks. So I couldn't get near the tower to look for the mark, but it probably would have been fruitless anyway.

 

On my way out, I spotted the following in the sidewalk (actually, part of the Stevens Creek Trail for walkers, joggers, and cyclists):

 

TCG.jpg

 

The triangle appears to be pointing SW of the transmission tower; i.e., just where the benchmark should be. Does anyone know what the "TCG 62" would mean? There's no reference mark mentioned on the NGS data sheet for HT1213.

 

I won't take up more page space by posting the location photo here, but if you want to see it, click on: Stevens Creek Trail.

 

And here's my CalTrans question: Since there's construction going on there (part of the whole 101/85/Shoreline/Moffett/etc. etc. redesign), a local CalTrans person could go to the transmission tower and look for the benchmark. As I mentioned, right now that area is dirt/piles of dirt/construction equipment. I don't know whether it will eventually be cleaned up and restored as part of the area next to the trail, or whether it will be paved over and become an on-ramp. So it would be nice to have someone look soon in case there's still hope. For all I know, it may already be gone. The latest report on the NGS data sheet is from 1967.

 

Patty

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You found some local surveyors traverse work point. He and he alone only knows what it all means. The fact that is happens to be near a bench mark is most likely just a coincidence.

 

I can guess from experience as we often marked our control points with a triangle and painted ID numbers/letters nearby for reference that this is for some property work in the area. Surveyors often place random traverse work points to tie into local property corners and other control. They then input this data into a coordinate geometry program to locate and or set property corners. It could from a GPS observation but more likely from a ground traverse where they have to see from point to point, the use a transit to measure angles and measure distance and compute coordinates for all the points in the traverse. A lot more complicated than this though.

Edited by elcamino

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Hi Patty,

 

As a continuation of what Mike has said, in construction surveying, we will often seek a safe place to set a semi-permanent station so that throughout the course of the job, we have a couple places like this that will "see" the entire job site, and not get wiped out during the course of construction.

 

After we have set these locations, our instrument, often a Total Station, which is basically a Theodolite with an EDM, (Electronic Distance Measurement) and sometimes a built in computer (some have external ones), is set over these stations and we turn the angles to and determine the distances to points that need to be built during the job. This is basically a form of open traverse from these points. We may locate property lines and rights of way, where a building is to be built, underground utilities and vaults, man holes, curbs, sidewalks, even where the lines will be painted on a road when it is all done, so proper lane widths match design etc.

 

Any thing that needs to be located on the site plan is physically located this way. When the job is done the point is abandoned and it is likely a landscaper will be charged with removing the traces of ever having been there. On really large jobs that are hurry up jobs, sometimes more than one survey and engineering firm is working in ensemble, so part of the paint job and labeling may stand for who's control point that is.

 

Sometimes, and Mike can confirm this, A private contractor will perform the work and may use their own surveyors. During and after, the respective State's DOT will perform a follow up survey to confirm things have been built to spec and verify as-built items, as well as perform any tweeks which signify the difference between what was planned and the actual build, because in the process of building, often changes are made on the fly.

 

As for the bench mark station you are looking for, depending on the plan, it may be lost during construction. However you could contact your State's Geodetic Advisor and inform her, Marti Ikehara , of the situation and she may instruct the DOT inspector on the project of it's presence and to be mindful of it, if it can be preserved. For all we know they may know of it and are using it for vertical control on the project. It may say so on the metadata page of the plan.

 

Happy Thanksgiving,

 

Rob

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I would agree with ElCamino and Evenfall. Surveyors commonly set points in seemingly random locations to complete a task or project. These points however are anything but random and they are placed in locations that will be relatively protected and able to be reused throughout the course of the project. 'TCG 62' is most likely the initials of the company that set the point and the number that was assigned to the point. The control points I set are labeled nearly identically, with a 'TCE', which are the initials to the company I work for, and the point number. Simply said, the triangle you found is a survey mark that may or may not have anything to do with the benchmark you're looking for.

 

As far as having CalTrans look for a mark for you: if it's within the construction area, CalTrans most likely already knows about it. They keep good tabs on benchmarks near their right-of-ways, although they don't always go out of the way to protect them. Progress (read: CalTrans) stops for nothing, including benchmarks. You may be able to ask someone to look for you, but your best bet would be to talk to a supervisor and to take a look for yourself.

 

Good luck on your hunt.

 

- Kewaneh

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Thanks for the excellent information, everyone. I think the idea of this being a semi-permanent mark is very likely, since the 101/85 project is taking several years. And I see now that maybe "TCG" stands for "Transit Construction Group" or something like that. I still wonder whether it's referenced to the existing benchmark or not. At least now I have a photographic record of it. (I also have a photo of a private company benchmark atop a hill overlooking San Francisco Bay just a mile or so away from this location. That one, however, was larger and had the company's name on it.)

 

So it's okay for me, as a civilian, to send a note to Ms. Ikehara? And say something like, "I'm an amateur benchmark hunter and am curious about the status of HT1213, which is near the 101/85 construction"?

 

I shouldn't have worded my other question in terms of a CalTrans person going out by himself/herself to find the mark. I was thinking more in terms that some of the geocachers on this forum are professional surveyors and might be able to ask a CalTrans friend to take them out there briefly to look for the mark. Then that geocacher/surveyor could file a report on Geocaching.com about the mark.

 

Patty

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