Best practice to measure GNSS Antenna Height used with tripod?

[jhframe]

I pretty much never put an antenna on an adjustable tripod, but for those rare occasions when I have no other choice, I go slant height. I keep one of the old Trimble collapsible height rods in the truck for just that purpose.

[MightyMoe]

Slant to the measure point.

[Norman_Oklahoma]

Use one of these together with a Leica adaptor, which has a standard offset to the ARP.

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• This reply was modified 2 months, 2 weeks ago by  Norman_Oklahoma.

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[Norman_Oklahoma]

My standard method is to use a 6′ folding ruler to measure up to the ARP and cut a hundreth. I’m using a Leica GS18 and I’m happy with the results.

Some crazy ideas..

1) Set up the base in the normal fashion, then take a rover shot on a benchmark. Return to the base and adjust the measure up as necessary to make the benchmark shot match record.

2) Set up a level adjacent to the base station monument and get a rod shot on it. Then set up the GPS base, adjusting the height until it is exactly at the level’s HI.

3) Along the same lines, and maybe just a little easier to achieve, use the level to establish an elevation reference adjacent to the base position. Setup the GPS base and adjust the level until it’s HI is the same as the ARP. Get a rod reading on the reference point and do some arithmetic.

[not-my-real-name]

I place the tribrach and rotating adapter (with optical plummet) on the tripod, center and level it. Then I take the tribrach and adapter off to measure the plumb height from the mark to the plate of the tripod. Finally put the tribrach and adapter back on, relevel, measure from the plate to the antenna reference point and add the two measurements. It’s not be the best way but it let’s me measure carefully.

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Historic Boundaries and Conservation Efforts

[timd1971]

WHY DIDN’T I THINK OF THAT!!! 🙃<div>

That’s why I love it here… all you guys are great!

That’s exactly what I am looking for in this particular case! (I use the hook/tape bracket with Leica Total Station and Tribrach, but will also get the hook/tape for the GNSS / tribrach / mount).

I understand removing/reinstalling the weight etc of the Tribrach may introduce slight error, but this sounds to be better than the usual off-plumb measuring route (not speaking of true slant calculation, but rough measurement).

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[half-bubble]

If it’s a single receiver over a ground point you are kinda stuck figuring out the best way to measure it up. I only offer the following as a technical detail and not for freshmen, strictly for live men, so to speak.

With a base rover pair, and using the base also for static, one could set up a variable height tripod practically anywhere with an HI of 0.00, like, not even “over” a point, then use a fixed height rover pole to locate other ground points. Send the base data to OPUS or DPOS, get back a position for the base that is basically a VRS with no measure up error, some good positions for the ground points. Now one may go anywhere nearby and use the ground points to “back in” a position for the base.

I learned this here on the board a few years ago. Thank you to Shelby Griggs and Mighty Moe.

[timd1971]

Welllllllllll……

Might as well swap the receiver out temporarily for a Leica with AutoHeight laser plummet and grab the height. 🤩

Guess could use a handheld EDM too.

Lots of great ideas guys. 👍

[pfirmst]

Definitely a Leica height hook, we use it for every tripod height measurement, no matter what instrument we’re using.

[john-putnam]

For GNSS, the Leica height hook is the simplest. Next up, the Leica TPS tape (<b itemprop=”name” style=”font-family: inherit; font-size: inherit; color: var(–bb-body-text-color);”>GHT196 DISTANCE HOLDER w/ <b itemprop=”name”>GHM007 HEIGHT METER) which mount to the tribrach foot and is calibrated for the slope and HI offset from the tribrach foot.

Just one thing to remember, for both the hook and tape, is that the offset from tribrach to the TPS height and the GNSS ARP is not the same. For Leica instruments, the ARP is 50.5 mm less than the TPS so you need to subtract 50.0 mm from the height hook measurement when using TPS and subtract 50.5 mm from the GHM007 height when using GNSS.

[RobertUSA]

Which brand and model receiver are you using ?

[WA-IDSurveyor]

We used fixed height tripods exclusively for all GPS work. I would highly recommend them. We never (outside of poor gps areas) had any vertical issues since we changed to fixed height tripods.

[timd1971]

Various Emlid receivers and custom Emlid M2’s with non-Emlid antennas. So different ARPs to APCs etc.

Therefore straying away from Leica Height Hook even if I can use it with Leica carriers noting the offsets of course. I know the Leica height hook is easiest when used with their equipment. My Robotics are Leica though with I use the Height Meter which would not be ideal for GNSS application.

It’s nice to hear what everybody uses though for ideas. REALLY liking the idea of removing tribrach temporarily to measure directly to the flat tripod face.

[dave-o]

I put my base on a tripod all the time and measure to the top of the tribrach adapter using the collapsable aluminum stick that came with it, usually to the mm letting Access convert. Then add the known extension and distance to measure point (ARP or BOM).

For those that strictly use a fixed height rod, is that only on a hard surface or do you compensate somehow if you have to push feet into the ground?

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dd

[timd1971]

“collapsable aluminum stick that came with it”

What does this look like? Is it the old Trimble pole @jhframe was talking about maybe?

Thanks.

[kjypls]

So, if a bipod wont work, how about a 2m fixed pole with tripod and Stedi Rest?

• This reply was modified 2 months, 2 weeks ago by  kjypls. Reason: Added picture

[jhframe]

“For those that strictly use a fixed height rod, is that only on a hard surface or do you compensate somehow if you have to push feet into the ground?”

If you’re talking about a fixed-height tripod, only the center pole is fixed-height, the legs are extendable, so you can mash the feet into soft ground.

[john-putnam]

I gave up on the fixed height tripods years ago. First, they never stay in adjustment. I would have to adjust the bubble each time I used them. Second, you still need to check the actual height on a regular basis. I think I get much better results with a well adjusted tribrach and careful height measurements.

@Timd1971, the ARP on most modern antennae is the bottom of the antenna. If you are using the Leica GRT146 carrier or the GRT144 w/GAD31 then the hook will measure to any APR. The 0.360 m offset is from the hook measurement point to the base of the threads.

[OleManRiver]

Does the antenna and software not have a slant height measurement routine. Before the GPS fixed height rods all the antennas and antenna/receivers I have used over the years all had multiple places and ways to measure to them. Anytime I am in that situation I still have the tent pole measurement stick that goes back to the old 4000’s and old ground plane antennas. The old recommended measurements back then were to measure the slant height in 3 different places. The old ashtech and Trimble antennas had these slots labeled . So three measurements in meters. To make sure they all fell within a certain tolerance. And on to 2 in feet. As a check. They had spots on our observation logs to input all this. I am trying to remember say the old 5800 were to center of bumper. All of these had a diagram so you could compute the true height to the antenna reference point or antenna phase center.

[MightyMoe]

I know they had those points to measure to. It was all kabuki theater back in those days. The elevations gleaned from GPS were very sketchy at best.

Today it’s more valid to pay attention to the height measurement, Still, .01′ is pushing any GPS measurement for heights and certainly for elevations; <1cm is a very good result.

Not to be a skeptic, but all the many, many miles of levels and GPS (RTK and Static) show the limitations of GPS heights and elevations. They have improved almost to the point of being useful for tight elevation control,,,,,,not quite there yet. I’m still not all that absorbed with measure up on a receiver, do it in feet, do it in meters and if those check it’s only what the measure point in the DC is set to that seems to be an issue.