Measuring tool for HI to bottom of a Trimble R8

I stick with fixed-height tripods for GPS work, but I had a river crossing project a few years ago that required reliable instrument height measurements, so I made a couple of bars out of scrap aluminum channel that attach to a tribrach adapter and extend beyond the tripod head for a slant measurement. With the appropriate dimensions of the bars and instruments, it was easy to calculate the vertical instrument height.

But why not use the place on the R8 housing -- it appears to be the bottom of the black separator ring -- to which all your observers would measure a slant height? Trimble publishes the appropriate dimensions:

GISJoel_GetItSurveyed, post: 405845, member: 11867 wrote: A tape stiff enough in windy situations.

I use a folding 6' ruler to do measure ups, partly because it works better on breezy days.

My PM3s has antenna ears that connect to a special pocket tape to measure the antenna height.
I have to get creative when I connect two 2meter rods together and get above the brush because the tape is less than 3meter in length.
You would think that all antenna would have a height mark on the side, but NOOOOOOOOOOOO, it just is not always that simple.

Use the option (Trimble Access) : Measured to Center of (black) Bumper.
You can set this as default in your survey style.

Chr.

Jim Frame, post: 405849, member: 10 wrote: the place on the R8 housing -- it appears to be the bottom of the black separator ring

christ lambrecht, post: 405889, member: 284 wrote: Use the option (Trimble Access) : Measured to Center of (black) Bumper

A Harris, post: 405883, member: 81 wrote: You would think that all antenna would have a height mark on the side, but NO

The drawing doesn't resemble the photo in that it doesn't show a black ring and you can't tell what feature they are dimensioning. The middle of the ring doesn't sound very precise, although better than most sessions in the vertical. I've noticed a similar problem on older Trimble antenna diagrams, too, that add confusion.

To get a precise check, you could pick a point that you can measure to, set up the antenna beside a fixed level rod, and fuss with getting a level on another tripod set to that height, read the rod, then set the level at the ARP height, read rod, and subtract rod readings.

The bumper is locaties where the grey housing ends and the white housung begins ... it's all in the Trimble Acces manual.
http://www.trimble.com/Survey/Trimble-Access-IS.aspx

First off, you should never try to measure to the bottom of anything on a tripod/tribrach, because you can't get a true measurement that isnt a slant height.

Second, the above mentioned photo of center of bumper IS correct. Trimble sometimes uses the stock photo for an older R8 for their antenna mockups. If you can ONLY input bottom of mount, Pythagoras will help you out there. As you'll know a and c, solve for b.

Lastly, there used to be a round, fiberglass measuring stick from Trimble that would read the bottom of mount HI, from the center of bumper. They had the calculation built in, and were cool until someone didn't know the specific application in which to use them.

Good luck.

I measure to the center of bumper and tell Access what I did. On the rare occasion I use an RTK rover I use a fixed height 2 meter pole.

I have an excel worksheet which converts center of bumper to ARP.

I like Jim's idea of extending a bar of fixed length past the receiver because then the ARP calc would not be dependent on make and model of receiver.

christ lambrecht, post: 405922, member: 284 wrote: The bumper is locaties where the grey housing ends and the white housung begins

But the bumper doesn't appear in the dimensioned diagram. So is the line to the bottom, middle, or top of the bumper? The other documentation tells us, but the diagram should have done that.

Use a 2 meter tripod. Take the guess work out of it. Sounds like you are splitting hairs over a millimeter or two with a receiver that isn't as accurate as you believe it to be. If you were that concerned with a "true" (repeatable) height of your points, you would be using a level.

Bill93, post: 405918, member: 87 wrote: The drawing doesn't resemble the photo in that it doesn't show a black ring and you can't tell what feature they are dimensioning. The middle of the ring doesn't sound very precise, although better than most sessions in the vertical. I've noticed a similar problem on older Trimble antenna diagrams, too, that add confusion.

To get a precise check, you could pick a point that you can measure to, set up the antenna beside a fixed level rod, and fuss with getting a level on another tripod set to that height, read the rod, then set the level at the ARP height, read rod, and subtract rod readings.

The bumper is the dark gray strip in the OP's photo, it is a couple of millimeters thick.

It is at the bottom of the 0.010M dimension in the diagram Jim posted.

I use a graduated rod that can collaspe to under 5 feet and extend to 8.5. It's marked in feet and meters. Works great

Dave Karoly, post: 405930, member: 94 wrote: The bumper is the dark gray strip ... It is at the bottom of the 0.010M dimension in the diagram Jim posted.

Yes, the bumper is obvious in the photo, and I figured everything out when it was said Trimble uses the middle of the bumper.

But I wanted to complain about drawings that wouldn't pass a careful inspection.

MightyMoe, post: 405933, member: 700 wrote: I use a graduated rod

A 4-section rod came with the old Trimble gear I got. It screws together and is marked in feet and meters also.

I made a spreadsheet to do the Pythagorean calculation and offset subtraction for the range of heights I typically use (with tribrach and tripod) in increments of 5 cm (10 cm would probably be adequate). It gives the value to subtract from the slant measurement to get ARP height over mark. That is pasted in the back cover of the field book.

Trimble is not the only ‰ÛÏvendor‰Û that sometimes appears to go out of their way to confuse some folks (those who don't/won't READ the Manual/Instructions, or don't take the time to ACTUALLY check things out on their own). Just as a conscientious Surveyor should check all of his Chains, Tapes, Prisms, EDM(s), Thermometers, Barometers, etc. One should take great care (and pride) in doing the obvious QC on Level Bubbles, Rod ‰ÛÏrun-out,‰Û Tribrach adjustment, and of course, making damn sure that he/she KNOWS what GPS Antenna they are using, and how to properly determine the GRP (Geodetic Reference Point [mark]) to ARP (Antenna Reference Point), value.

It all comes back to procedure, Procedure, PROCEDURE!

To the extent to which a Surveyor develops and uses GOOD Procedures, those ‰ÛÏhabits‰Û (SOP, MO [modus operandi]) not only minimize blunders and [certain] systematic errors, but goes a long ways toward catching such errors [essentially] before they happen (or get into the field book or data collector).

Somewhat off topic...This 'kinda' reminds me of an old quote, the origin of which evades me.

‰ÛÏGood Surveys don't need to be adjusted, and no amount of adjustment, will turn a poor survey into a good one.‰Û

Staying ahead of the gremlins ‰ÛÏmight‰Û be a little harder than it was 100 years ago, and then again, maybe NOT!

Loyal

Trimble makes it fairly simple. There are many measure points for trimble gear. The R10 has an extendable measure point. The L1/L2 can be measured to the bottom of a notch. The data collector will adjust for slope to each point.

MightyMoe, post: 405941, member: 700 wrote: Trimble makes it fairly simple. There are many measure points for trimble gear. The R10 has an extendable measure point. The L1/L2 can be measured to the bottom of a notch. The data collector will adjust for slope to each point.

Absolutely true Mighty!

However, I have SEEN folks measure to the "notch in the (big) ground plane," and enter it into the data collector as a "vertical GRP to ARP."

Certainly NOT Trimble's fault, but some folks have little (if any) meaningful training on the gear/software that they use on a daily basis.

Loyal

And enter it in as the bottom of notch on the L1/LI antenna without a ground plane but Imput it in as if it has a ground plane attached. Seems to be infinite ways of messing it up. It never hurts to make some simple checks.

As expected, this community response is awesome.

This thread can close now. I now have enough info to proceed. I also understand better how important it is to be precise with this group.

I also want to ensure I'm doing the right thing, and realize this is mm issue with some measurements, but I want to remove the major blunders that I've seen several times. Photos of the setup have been my most simple check (MightyMoe).

Jim Frank - I "try" to use fixed height tripods set to 1.5m with a 25 cm post for a total height of 1.75meters, but I'm a nut for procedures (Loyal) and want my guys/gals to check with a ruler. (Son of a Carpenter). The gear is stored in pelican cases, so i need a small, metric tape /folding stick solution that is small and portable.

Raybies - I get it now. I bucked the whole slant height thing until I got a solution reasonable for procedures to follow. The Survey Style fixes all ills (thanks Christ).

Mark - I will continue to look for a metric version of the folding 6' ruler noted in your link. I have not found a tape suitable to hold still under windy conditions. The stiff nature of that style of measurement tool will meet my needs. Metric remains a must to reduce something called Units that tend to befuddle even the PhD's i work with.

Bill93 solutions are great. I'll have to pass on a long ruler for portability though (thanks to Mighty Moe too). And a spreadsheet for Pythagoream will not cut it for my crew - thanks, but I have to pick my battles.

I have persons who still use tripods/tribrechs and will have to use the slant height and set the survey style as mentioned by Christ. Great idea. I thought I knew alot about styles - but still learning.