Advice on calibrating a Fixed Height Tripod

When you receive any pole or fixed height tripod from the factory I have found the bullseye bubbles are too loose. Run the screws in a couple of turns then calibrate the bubble, it will stay in calibration much better because there is pressure against the screw threads.

I don't use fixed height tripods because I find a tripod tribrach is vastly superior although it takes care to get an accurate height, isn't that what Surveyors do? Fer cryin' out loud. If the project requires the use of that gangly aluminum nightmare then you have to use it. The ones I used were designed to rotate so you can adjust the bubble (center the bubble, turn 180 degrees, move the bubble halfway to the center, recheck, etc.)

the trick to a variable height setup is measure the height in feet then independently measure the height in meters. Then do the math, any blunder becomes readily apparent. Doing that I've never had an undiscovered bust in 15 years. Do not measure the meters then find the feet on your tape, that defeats the whole purpose.

I agree with Dave on the adjustment routines for fixed heights. I have always found you just have to check them with a hand bubble and rotate multiple times to get them in adjustment, at least at the beginning of every single work day, and sometimes every setup for precise work.

Obviously the NGS and other orgs require fixed heights for certain work, so sometimes the decision is out of your hands.

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Posted by: @dave-karoly

the trick to a variable height setup is measure the height in feet then independently measure the height in meters. Then do the math, any blunder becomes readily apparent.

This is great advice as well. I measure in feet, book it, remeasure in meters, book it, and then enter meters in Access with "m" after the value, watch it convert to feet, then check against my booked feet value. I haven't entered an incorrect height since I began this method.

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Posted by: @gisjoel

What else should I be doing??ÿ

Checking the rod bubble routinely is what. There are more ways to do that than Carter has pills. You can check it with a rod level, but what are you using to check the rod level? I'm thinking that one of those hang-on-the-wall-jigs would be a good investment for you.?ÿ ?ÿ?ÿ

I'm generally with Dave on the tripod vs. fixed height rod thing. But I know that you are often helicoptering into your sites and weight and bulk are a big factor.?ÿ

Over the years I have found the Seco fixed height tripod bubbles to be a joke.?ÿ No matter what you do or how gentle you are with them they just will not stay in adjustment.?ÿ My practice is to basically re-adjust the bubble, by the rotation method mentioned by Dave, at every setup.?ÿ To alleviate some of the frustration I purchased a 8' heads up bubble which I clamp on the pole thus eliminating the need to recalibrate every setup.?ÿ I carry it in a vest pocked of case so it does not get beat up and stay in adjustment.?ÿ In your case I would at least upgrade to a better bubble for checking, the vile on your tripod is 10'.

For the most part I have abandoned them and just use a tripod and tribrach.?ÿ Horizontally the setup is better.?ÿ I've never really been sold on the 'Fixed' height measurement thing anyway.?ÿ For NGS work we routinely checked their heights and replaced tips.?ÿ Using the Leica tape hook or tribrach tape I can get a true vertical measurement to mm precision without problem.?ÿ I just make sure to check it at the beginning and end of the setup.

A fixed height can be set up within the ability of the operators eyesight even when out of adjustment. Do the 180 split the difference method and call it good. You will be as close as anyone with an off the shelf midgrade tribrach.

If you can get hold of them the old Wild GST70 tripods will keep their adjustment very well. We have four - new points made to suit the instrument they are being used with.

For mi-accuracy work when you want as few bits as possible to carry they are just fine.

It looks like I'm in the minority regarding the Seco 2m tripods -- I use them exclusively for static work and for my RTK base.?ÿ I don't have a problem with the bubbles, because they're so easily checked by rotating the center pole.?ÿ And the few times I've checked plumb with a transit, I've found less than a mm from tip to top, good enough for me.

My only gripe about them is that the soft cases for my older ones (circa 2001) are too short -- getting the case to fit around the end of the pole (sans tip) is an exercise in frustration, scraped knuckles and lots of bad words.?ÿ My newer ones (circa 2007) are cut much more generously, with inches to spare.

Edit:?ÿ I only have the true fixed-height versions, I've never used the ones with the collapsible center pole, so my comments don't apply to the latter.

@dave-karoly

Thanks Dave.  Will take this info to heart.  I know this is what surveyors do, and wish there were 10,000 more of you out there tied to us in GIS with the same access to these places where Ologists visit every summer.    The tools at their disposal are getting more and more precise, and the setup over a control is the monumental first step I'm trying to tamp down to ensure the right decision is made given access (boat, plane, helo), long occupation on a control from the 70's or late 90's.   Fixed Height tripods take the slant height out of the question (though, as you stated, is always taken alongside our fixed height measures).  We also have folks using the UNAVCO, low profile fixed heights, which I hate due to their Low profile, but I'm doing the best we can.  

Thanks.

@jim-frame

All of ours are collapsible center pole types.  We also were lucky to pick up those solid Orange cases (no longer manufactured) which we ship/transport our fixed height rods in.  Through airports, boats and trucks, this has kept us, i think, in better shape when we arrive on site.  NRCS up here, also heavily invested in remote RTK setups convinced me 8 years ago that this was the way to go, eliminating the two biggest issues OLOGISTS face.  Getting over the mark, and ensuring the HI are as good as we can expect.  Were not doing boundary work (nor ever will).

We do snap on (usually with flagging tape), this 40' vial which I'm learning now should be a 10' version.  I'm chasing that down.

We do have a calibrated wall system, which works 2 weeks before the system gets shipped out from my office to the site, then there is the field....

I can't have tripod/tribrachs for our BASE setups, especially when,

@john-putnam

thanks John.  Looking for those 8' heads up bubbles now.   Excellent tip. 

We check heights every spring, change out tips. We exclusively use Trimble receivers and processing methods, including the online gnssprocessor which also keeps our OLOGISTS as much as possible, on the right height.

@norman-oklahoma

We do have the wall setup here in my office which we check with our hand bubble on a calibrated rod set in that wall jig, which we then translate (for a better word?) that hand bubble over to the center post on the Fixed Height rod.  We use snap on type hand bubbles or use flagging tape. We ignore the bubble that comes with the Seco fixed height, and should consider, removing them altogether hearing from this thread.

Yes, were schlepping gear long distances.  I'm forcing our ologists to suffer a little more weight on a fixed height (mass is also a good thing for stability) and using hard cases for shipping the fixed ht., rover rods for security.

Thanks Norm.

Sorry, hit return too fast.?ÿ?ÿ

I meant to finish that I tripod/tribrachs are more risky for the non-surveyor types.?ÿ?ÿ

@jim-frame

I still use three 2 meter two section solid poles that came with my PM3s for static along with the collapsible poles.

The solid poles work much better for me when there is high wind and I am able to extend as needed to get a better horizon.

0.02

@dave-karoly

We ALWAYS use tripods with tribrachs (no optical plummet) for precise work. We have various rotating plummets to center over points. 

I do use a rover pole with a three leg mount for things like Lidar/photo control, these can easily be checked by loosening the clamp slightly and rotating the pole. If we need a little better accuracy from the rover pole I will take an observed control shot, then rotate the pole 180 and repeat. I actually found that my bubble was in good adjustment, but the rod was slightly warped, as I would get a consistent difference when rotating 180, same magnitude, same direction. 

I use a fixed-height every day for my RTK base.?ÿ I occasionally calibrate it by taking the legs off and hanging it on the wall bracket I use for my poles.?ÿ Big hassle, and I admit it doesn't hold the calibration very well.?ÿ If I'm doubting the bubble I split the difference like @thebionicman said above.?ÿ I can't remember how it's configured, but is there some kind of aftermarket bubble that could replace the one it comes with, so you don't end up duct taping something to the side?