Establishing a base coordinate without a reference

I am a new user. I have read most of the docs as well as a number of threads here on the community forum. I am a retired mechanical engineer with a fair bit of programming experience. I am now farming and trying to setup an RTK system to support on-farm equipment guidance as well as property boundary location. But I am new to surveying and to using a gps. I also confess that I have acquired a pair of M2 units as well as two Helix antennas and two LoWra radios, but I have not assembled or tested the system yet. I plan to do that shortly. For now, I am working my way through what needs to be done to achieve good results.

I understand that I don’t need accurate gps positioning for farming applications like spraying, fertilizing, planting, and plowing. I only need precision perhaps to plus or minus 2" or so. On the other hand, I do need accuracy to locate survey stakes and establish property boundaries. It’s Important to understand that farmers in my area like to relocate survey stakes in their favour so I want to be able to know if they are properly located before creating any needless arguments.

I do have access to a nearby concrete survey monument that I can use to establish a good reference location and coordinates.

I am thinking that I could install my planned RTK base, let it figure out where it is using its averaging function on its own, then accurately locate the rover over the cement monument, and then manually adjust the base location parameters until the rover coordinates become accurate. But I cannot figure out how to do this from the available information. Maybe it’s something that will become more obvious with time, but the planting season is fast approaching and I’d like to get my system up and running as soon as possible.

Can anyone point me at what I may have missed and perhaps also correct any misunderstandings you think I might have about how this works?

Thanks in advance.

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In most countries this a legal matter, and cannot be repositioned by other than registered surveyors. That guarantees an unbiased 3rd party with deep knowledge of the subject.

However, it is completely fair game for you to check the boundaries. Just don’t move anything.

I would do the following:

  1. establish your m2-pair on the monument and your own point of reference respectively. Now you can precisely and accurately determine your own local point. Log for at least 2 hours.
  2. you can average in RTK mode, or post-process. I like to post-process, as it gives me a lot of freedom. Here you just specify the base location of monument and of course the height of your M2 poles, and you will get a precise position.
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Yes, it is illegal here in Canada too. But that doesn’t seem to stop people from doing it. You can rest assured that it will certainly stop me. But it will also give me a great deal of leverage when and if I discover that it may have been done on any of my land. I’m fairly certain the stakes will magically get moved back when I point out that I have checked them myself and therefore I’m planning to have a professional surveyor check them and then report any findings to the authorities. But I would never do that without evidence. Hence my desire to be able to accurately locate them. There are other like minded neighbours in the area with a similar need.

I have seen this same advice in the docs and elsewhere on this forum. I think I must be missing some knowledge here. Should I be reversing the base and rover designation in your example? Also, since the specifications say that the M2 gets a very quick lock, why do I have to log for 2 hours if 5cm (+/- 2.5) accuracy is plenty good enough for my needs? And why can’t I simply enter the exact location into the configuration menu for the unit?

In other words, I guess I always assumed that the averaging was required when the exact position was NOT already known and that the averaging was basically a way of determining a more accurate position by averaging a very large number of positions over a long period of time. Apparently I am wrong about that, but it’s not obvious to me why that should be.

Out of curiosity, I wonder what would happen if I enter a hard location that is outside of the normal range of the unit’s actual location? For example 10 meters away? Does the unit know that is impossible and go into error mode or does it simply accept the false location and build it into any rover locations by translating them 10 meters away too?

I understand how post processing has advantages, but I had thought that post processing was something you did to analyse the data after downloading it to a computer. So I was hoping to avoid that because I don’t have the required software and don’t know what the raw data looks like.

In the case of averaging in RTK mode, I am fairly certain I saw that in the setup docs. If that capability is built into the m2, then that is my preference. I just don’t see why that takes 2 hours and I don’t know which one is set to be the base and which one is the rover. I assume that the one on the known location must be the base, and I assume that this can either be designated permanently by physically swapping units, or temporarily via a simple toggle in the configuration menu of both units. But I’d appreciate it if you could confirm these assumptions for me.

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If you are averaging in RTK mode, and your base is surveyed in, it doesn’t take that long to average. Here in Ohio, we have a state ran CORS network which all of their bases are surveyed in. If I connect via NTRIP and do a 5 minute fix average, I get within 1 cm from the actual LLH. With this, I do not do any post processing.

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The overall process is that you should always put your base over the point for which you know the coordinates and enter those manually. From there the rover can be used to locate the relative position of unknown points compared to the known one. The point on your property is still the unknown one.

As for observing for a long time, it’s all a matter of how precise you want your point to be. Since you’re setting up a permanent reference, more observation will give a better result as the different, varying signal uncertainties will be better resolved.

Out of curiosity, I wonder what would happen if I enter a hard location that is outside of the normal range of the unit’s actual location? For example 10 meters away? Does the unit know that is impossible and go into error mode or does it simply accept the false location and build it into any rover locations by translating them 10 meters away too?

The receiver will assume the position you feed it manually is reality. The discrepancy between what it calculates and what you tell it is true is assumed to be outside interference. Atmospheric and ionospheric factors, multipath, and other factors do affect the signal permanently and there is always variability expected for this. For example, some researchers where I work use pairs of receivers, one at ground level, and one above on a pole, to measure snow properties. The difference between the two signals can be used to model the snow cover.

Also, on the more legal side, document the before/after potential stakes moving. It’s actually a criminal matter and I personally wouldn’t hesitate to report any shenanigans.

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I also agree, and professional surveyors are well worth the money. I am also “playing” surveyor this summer to find if property pins have moved. But if I do find any fishy ones, I will be getting a real surveyor with the authority to do something about it.

But at least now I can check, and only have to pay the pros if it really needs correction.

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Look into OPUS, Online Positioning User Service, to obtain a cm-accurate absolute position without any local references or NTRIP:

Note to EMLID support: after researching & thoroughly vetting OPUS as a possible solution you might consider adding a reference to it in your docs as it helps solve a problem faced by many stand-alone Reach users, especially those who aren’t professional surveyors.

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Well that isn’t going to happen. The known point is beside a fairly major highway and furthermore isn’t even on my property. I’m not leaving my m2 there!

I really only want to use that location long enough to locate and mark another point up close to my home where the base can be located for use as needed.

I will do that!

Thank you.

I’m sorry, I must be thicker than usual today.

Since I plan to do my setup at a known location, I don’t see why it takes any time at all. The position doesn’t have to be resolved. It is exactly where I manually told it that it is. What am I missing?

Thank you!

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When I do these benchmark-runs I would usually spent an hour in my car next to the monument.

So basically have my rover set up somewhere safe, or under supervision, and then I go to the reference monument and set up.

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Instead of OPUS, you can use NRCAN’s PPP service - it is much more robust and file-formatting tolerant. If you really do not want to leave a base station on a known point for enough time, do a single static observation on what will become your permanent point. But in that case, make your observation 4-6 hours for best results, and wait for the RAPID solution from PPP.

Since I plan to do my setup at a known location, I don’t see why it takes any time at all. The position doesn’t have to be resolved. It is exactly where I manually told it that it is. What am I missing?

Do you have precise centrimetric coordinates for the location you want to use as your reference? If not, this is not a “known” point. Known in this context means a point that has been measured before and has been validated.

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I do not leave our receivers or robotics on the side of a road !!! John, if the “concrete monument” is truly a passive Canadian control mark, you could look it up here:

There is also the Canadian CORS network CACS (Canadian Active Control System) just like here in the USA (NGS CORS). Both have an online PP service (USA OPUS, Canada CACS). Here’s Canada’s:

If the “concrete monument” is indeed a passive control mark, just set one of your M2’s at home on your mark and set the other on the control mark and babysit with it. Then you can use the online processor to PP both as well as PP the baseline with the free RTKLIB available from Emlid. You could also use the Canadian PPP service for both.

The beauty of tying all surveys to any National Spatial Reference System is that you will be able to reproduce and retrace the original survey, 1 year from now or a 100 years. All surveys our firm has done since my dad started this business in 1972 have been referenced the NSRS.

There’s several ways to “skin” this cat ! Also, I would contact some local Surveyors and maybe buy them lunch or dinner to get some advice. There’s also a “science” in just setting up a tripod or bipod over a mark. This is the most important procedure in any surveying task, all errors begin here !

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John,

I am not a surveyor but use my RS2 Units in Utility Construction/Road Construction. My method is as follows and I look forward to feedback if I’m making some bad assumptions.
Since a surveyor has put down control points for the project, I simply go out and set up the Base and let it get a good reading on the satellites. Then I go to the control points and take a reading making sure that the mode is in FIX. I then do the rest of my surveying and if I think I will need to return I mark my base position. I then download the data to Autocad Map3d, identify the proper location of the control points and then move my data points as a group to where the control points from the field are aligned with the proper control point location. This method usually results in accuracy between the control points of an inch or two. Since I have noted the coordinates of my base unit, I place that point on the map before I move the group and after the group has been moved I make note of the new Base coordinates. If I have to return to the field I set the Base back up over the prior marked spot and enter the known coordinates into the Base. This has worked well for me. QGIS is a great free piece of software that you may find useful as well.

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Why not occupy one of the Surveyors control points and check in to his others.

Seems that would be far simpler. But if that works for you, then continue as such.

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HI Bryan, your question to Frank is not obvious to me. Do you mean: Put the base on a surveyor control point, and then move the rover to the other points?

Hi Frank, that’s sort of what I have in mind to do. (see also my question to Bryan).

I plan to put my base on a known point. Wait for a fix, then using the Rover, I will locate a new reference point up on a high point near my farm house where the LoRa can reach the rest of my farm. The rover will tell me what my “new reference point” is. I will then move the base to this new reference point which will become the home spot for the base for all future work. Ideally, it won’t be a pin. It will be a permanent post where the M2 Base can be placed whenever I use it. This spot can be reached by WiFi from the house and also has a convenient 120V power outlet for the M2 usb power supply.

I don’t know if I am right about the next part of this… I am hoping that the resulting 1cm accuracy of the new base location can be recorded and then plugged into the base coordinates field of the base unit. I guess we will see.

All - I am sorry for my absence. I’ve been tied up for a few days. My bride is painting our great room and I am getting far too many assignments. That doesn’t even begin to cover all the dirty looks I get whenever I “play with those stupid GPS toys” of mine. I guess I can’t complain though. After all she is the one doing all the painting not me.

I’m hoping to be able to “play” a bit more today / tomorrow.

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How do you plan to determine your known point? If you can set up somewhere on your property and then get a reading on that known govt marker you can the adjust if you have the software. If you don’t I’d be happy to help out with the correction, unless the forum tells me that my workflow is off.

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The control points are right by the side of the road, otherwise I would.

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