Not getting accurate survey results (Reach RS+)

In my case I continue to be torn between a single-band receiver and a multi-band receiver… as the price difference is large…

I always work outdoors… I don’t do surveys in the city… I don’t do surveys in places with high vegetation… but I often do surveys inside open pit… often the depth of these open pits is also 100 m below ground level and the walls and the bottom are in white stone (highly reflective)…

In my mind you might as well consider yourself in a suburban environment, potentially even worse, because no signal will penetrate the sides.
Also, moving closer to the walls could introduce quite a bit of multipathing.

Depending on the size of the pit a multifrequency GNSS solution like the RS2 will give you acceptable performance, but if narrow, a total-station is probably a better solution.

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The station can always be placed in a position with the entire sky, at 360 degrees, completely free.

Yes. The rover may need to measure points close to the walls. Usually the open pit is not closed on 4 sides, at least 1 is totally open. Usually the upper mouth is, at least, 150-200 meters wide.

Doing tests with the simple GPS of the mobile phone, even in the worst situations, however 12-15 satellites are always seen.

Nevertheless the multipath always remains a source of error because the reflected signal travels farther to reach the antenna, the reflected signal arrives at the receiver slightly delayed. This delayed signal can cause the receiver to calculate an incorrect position.

I understand that a multi-frequency receiver solves this problem. Correct ?

Remember there a big difference between seen and usuable.
If you need to be centimeter precise, the visible sats need to have a an SNR of 35-40, and they have have to be distributed somewhat evenly across the sky.

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It doesn’t solve it completely, but it gets smaller for sure!

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The L1 frequency is relatively slow it is not very effective at traveling through obstacles, on the other side L2 frequency allows the signal to better travel through obstacles such as cloud cover, trees, and buildings however L2 is not yet complete because of this it cannot be used on its own and must me used along with L1 frequency, knowing that the most advanced signal L5 is come to reduce some problems like providing improved ionospheric correction, signal redundacy, improved signal accuracy and intereference rejection but it is still in its infancy, with deployment scheduled for 2021, combined frequencies will also allows for faster initial signal acquisition than with L1 alone, for that the RS2 will have a very good future regarding accuracy.

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I don’t need “very high” precisions. 10 cm error on X, Y and even Z is ok.

Is there an app with which I can test the satellites I hook from a position and their SNR ?

RTKplot from RTKlib can show you it, if you feed it with a converted ubx raw-file

There is no smartphone app?

Something like GPSTest app ?

“C/N0: The carrier-to-noise density is a measure of the signal strength transmitted by the given satellite.”

there are plenty, but again, those are pretty basic, and most will just give you a seen/not seen scenario.

However, this one allows you setup obstructions, so you can get much closer to real-life (sorry, web-based):

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L5 has about twice as much power as L1, and since L5 does not carry military signals, it achieves an equal power split between its two signals. In this way, L5 lowers the risk of interference and improves multipath protection. It also makes the data-less signal easier to acquire in unfavorable and obstructed conditions.

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@ Michael Lambert you’re right

You might as well just shoot for equipment that is at least cm accurate like Reach/M+/RS/RS+ and RS2. I know you say the cost is significantly different, but really, these are the BEST deals you will ever find compared to what was available BEFORE Emlid provided their product solutions. Take a look at pricing of brands like Trimble, Leica, Topcon (and even many other lower costs options), and you’ll be quite happy with Emlids pricing.

Now look at the price of a “Robotic” Total Station… at least $12k for a new one and it just goes up. You can find used ones also, but you will have a lot of research to do. You can get a non-robotic Total Station for less money, but that will also be quite expensive but may serve your purpose just fine and mm accuracy as a bonus.

They have LiDAR also, but is VERY $$$$$. (Drone with LiDAR?)

Leica makes a 3D Disto that can record and layout points in 3D XYZ space which may be something you can look at…but $$$ also $8k?

Take a look at a Leica Disto S910 Pro Pack also. (Get pro pack which you need the encoder mount)(about $1500 for everything you need) Somewhat like the 3D Disto, but manually not robotic and limited to 30 points at a time. Works with their app or you can use third party pro survey software like FieldGenius. Keep in mind works locally in xyz coords, so you’ll have to manipulate etc in cad software etc. It does not have GPS or GNSS, so if you need, your back to looking at a RS2.

Maybe there is a dealer nearby that can let you test the equipment for your needs? Maybe contact Emlid to see if possible to do this with there equipment and a return policy if it does not suit your needs? But good luck as it doesn’t seem the RS2 is “immediately” available anyways as too new?

Sounds like working down in a hole, and as @wizprod mentioned prob worse that urban areas.

Sounds like you may not need GNSS location immediately during work, but definitely XYZ point location locally, then get some GNSS CONTROL POINTS and shift or ROTATE/TRANSLATE/SCALE XYZ points to them in software later? FIELDGENIUS/QGIS?

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My need is to “measure” distances and height differences between

  1. a point on the field that I choose as origin (0,0,0)
  2. some Ground Control Points that I spread on the field

That’s enough.

At the moment I use a laser total station (20 years old) that costs me zero, it does its job very well but it has 2 problems

  1. there must always be an optical view between the station and the point I want to measure
  2. 2 people are always needed… 1 must stay at the station and aim… 1 must walk and put the pole on the GCPs…

Moreover the measurement operations are slow… if there is sun or wind aiming is not easy and is slow…

What I would like is to be able to take these measurements without a second person in the field and faster…

Time to upgrade.

In the past I needed days for a survey, point by point.

Now, with the drone, it takes like 15 minutes.

I just need a system to take some measurements (GCPs) to scale and check the drone result… unfortunately I can’t find it at a “small” price… is emlid right for me ? what product ?

The described working environment (in a pit; near pit walls) will be challenging for any GNSS receiver, so I would lean toward the Reach RS2 multi-band receiver. That doesn’t rule out the usability of RS+ or M+ single-band receivers though.

The more you spend, the less errors you will encounter in your work, and the less ‘extra’ GCPs you will have to collect in case the more difficult ones don’t work out.

So the right Emlid product for the job is the RS2 Survey kit, and it is up to you to determine the right product for your budget (RS2, RS+, M+).

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