Hi Emlid community,
I’ve been searching for a way to accurately measure base station -ARP point in a mm precision fashion, but yet did not find any “good solution”. I’ve seen a lot of videos and explanations to level out tripods and bipods a lot (which is good) to get most of accuracy in XY positioning, but I haven’t seen any comparable way to deal with the Z accuracy, which by the way, is the less accurate measure achievable, from the three (XYZ), in a GNSS survey mission/project.
I’ve seen people measuring must of the times, the slant height, (which is very prone to errors and a poor systematic procedure), that later (as mentioned by them) is used to compute the true height (nobody mentions how to it and how precise it is). The latter, does makes me a bit surprised, after seeing a lot effort and tec to level the antenna and then missing one of the most fundamental measures to acquire (ARP height).
The best video I’ve seen so far, that may help (I’m not sure) to establish a pre-determined and fixed height is this one here.
Now, there maybe (“for sure”) other or better techniques to measure ARP with mm precision, and this is why I wanted to share you guys my point view and concern, to help me find a solution and buy the right accessories to go along with Emlid receivers. The latter, leads me then to the second question:
Which are the best tripod set-up one could have or use to address the main question of this topic?
Why Emlid doesn’t have those (tripods and/or bipods) ?
And another important question, that could follow the way tripod setup is done on the previous video is,
Is it really important to have a tribrach equipment for a GNSS antenna after levelling out as demonstrated in the previous video?
Forgive me for my other questions. But, if it is that simple, why we always see the use of a tribrach as in the Emlid video and which setup is more precise? How expensive the solution of Emlid video can be compared to the solution of a tripod with a fix pole height and how to obtain accurate height ARP measure in that setup?
Is the Emlid antenna compatible with configuration you provided?
You are most kind in taking time to help me. Thank you.
The tribrach setup is when used with the traditional heavier tripods typically used with heavy total stations and backsight prisms. But yes you can use those too with GNSS receivers. Just not as straight forward to measure your base antenna height which your initial question is asking as the tripod is variable in height. If concerned about stability, can apply sandbags or weights.
I understand you are trying to be as accurate as possible and avoid accumulated error… but may be suffient enough to use a rigid measuring tape from point up to the bottom of the receiver vertically best as possible (to it’s ARP). Or calculate using slant but yes introduces error. I personally am fine with just measuring vertically PLUMB from ARP down level with side projection of point as close enough for my needs.
Maybe someone will jump in with a better procedure.
The tribrach setup is when used with the traditional heavier tripods typically used with heavy total stations and backsight prisms. But yes you can use those too with GNSS receivers.
Alright then. So the tribrach is used with the heavier tripod solution, for instance, this one. Which is much cheaper than the (tripod+fixed pole) and we then have to add a tribrach, for instance, this one or this laser one and some other accessory I may be missing (not sure). Correct? This solution can be around 250$ cheaper then the tripod+fixed pole solution, do you agree?
But then, we have to find a way to vertically measure the height with a measuring tape… Thus anybody tried to measure with some kind of laser ruler ? But how accurate and easy would that be ?
PS: What do you think about this solution compared to the one you gave me (tripod+fixed pole) ? It is much cheaper. Does it achieve the same objective, to be stable (i.e., levelled) and accurate measurable in height?
P.P.S: Maybe this extensible grade rod could be a solution to vertically measure tripod height in relation to ground marker? What do you think?
And then there is the laser ruler…
Ebay has a lot of these options cheaper. Amazon may also. Prefer laser tribrach versus optical target. Unless genuine Leica or Trimble tribrachs, most are just chinese anyways. Some tripods heavy. Some lighter. Some wood, some aluminumn, some fiberglass / carbon fiber composite, some cheap, some $$$$. They each have characteristics of shrinking expanding in cold/heat that may affect your tolerance.
Its all in what u need for your tolerance and if u need to lug everything or ship or take on a plane?
Grade rod overkill versus just using a tape.
The fixed 2m pole with tripod easiest and most used for gnss.
Agree with @timd1971 Unless you already have and use another setup, get yourself a fixed pole and quality bubble level. Verify with a tape that the pole is actually exactly the length it is claimed to be. Calibrate your bubble (youtube is your friend) and you will be able to utilize your gnss receiver to it’s limits of precision.
The cheapest way to get the accuracy you desire is to get a 2m rover rod (fixed or telescoping) and an antenna rod tripod. Eventually you may realize the the value of the improved stability and ease of use of the larger fixed height antenna tripod but get started with the rover rod and rod tripod.
Additional tip for the rod tripod: replace one of the leg bolts with a bolt and wing nut so you can remove the third leg when you want to run a little lighter and faster as a bipod but reattach it for use as a tripod.
This ist the most accurate way to measure a base height. It’s only in German, but maybe vom generated subtitles are available.
I think it’s not handy enough for your daily use.
