Reach M2 as a replacement for RS2

Hello y’all

I’ve seen a lot of projects here using Reach M2 in a base+rover setup (plus the GNSS helical antenna and the LoRa radio for both of them) for land surveying, but I don’t see a lot of feedback from the users (maybe I’m not looking right; if there’s some feedback, please somebody show me).

I’m asking because I’m planning to: OR creat a NTRIP base using an M2 (don’t have any NTRIP base near me) and use another M2 to survey, OR use a pair of M2’s as a base+rover setup.

I know that the ideal in this situation would be using a pair of RS2, they are built for this kind of job, I’ve some friends that use them (and OH LORD that’s some good shit), but my I’m looking for something cheaper for now.

Thank you!

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They are great static receivers for my use as long as they are in non multi-path areas. I use the Harxon GPS 500 antenna with them. When I’m able to get out of the office, I use them mainly as a static baseline with my JAVAD Victor LS rover even when using our state RTN VRS service. There’s places where there is non cellular service and this gives me a closed loop to verify my rover position. I’ve had great loop closures after PP. Its a great way to make sure that the rover position has good accuracy. Most of my baselines are usually less than 3km based on project size. Short baselines for PP are your friend.

From my experience the M2’s (or for that matter any receiver) don’t like multi-path. It’s the software and GNSS module that can resolve the signal ambiguities in high multi-path areas and give a confident solution.
Our JAVAD receivers rule in these conditions.

I’ve used the RS2 a few times with the RTN and is a very capable receiver in open areas. But as said above, the Emlid receivers don’t like multi-path. Emlid doesn’t have any point verification like our JAVAD receivers.

There software isn’t very land surveying friendly. It doesn’t have any COGO functions yet and their base setup isn’t very friendly either, but supposedly they are working on both issues.

I’ve bought the FG software and have used it with the Emlid products, it’s very good.

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What type “land surveying”? What Bryan does is completely different than I do. He is doing “legal” type boundary surveying where I am doing topographic surveying for drainage installation.

He uses the COGO function of software where it has no real advantage in my application. I use software that records the boundary of a field with LAT/LON/ALT every 10 feet, I then change over to interior and do an S pattern in the field every 25-50 feet (recording LAT/LON/ALT every 10 feet linearly). I pull this data into my desktop software and it creates a topo map of the field that I can manipulate for land sloping/surface drainage/subsurface drainage.

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What antenna are you using? In my experience with M2, the choice of antenna has a huge impact in how much multi path you see (in the same scene).

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Hi Bryan! Today I’m using a pair of RS+ (base+rover config, with the base static on a know point). I had a lot of trouble with multi path.

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Hello JP! I work with both situations. Legal type boundary and some surveyings for landscaping projects (Sorry if I wasn’t clear, english is not my first language.)

Hi Christian! Do you have any suggestion for the antenna? The ones from Tallysman look a little bit too fragile in my opinion (the M2.5 thread).

I agree Christian ! That’s why I got the Harxon. The helical antenna is a good antenna, but it’s not in NGS calibrated list. I’ve had some problems with vertical accuracy on the helical. Best I’ve gotten is 5cm, usually it’s worse. But long occupation in static will get better but usually 3+ hours. But as I said above, it’s mainly the software and GNSS module that can resolve the signal ambiguities in multi-path areas. JAVAD is the leader in signal processing.

Have you tried putting on a calibrated antenna?

If you get another receiver, you’ll have a closed polygon to verify the rover’s position in multi-path areas. It’s best to get a commercial PP software to use. Christian uses EZSurv I think. I use either TBC or JAVAD Justin PP software, mostly Justin as it has a phenomenal processor.

Yep the Harxon. Vertical accuracy is far better usually less the 3 cm for 1 hour static

If you don’t need something IGS calibrated, go for something like a Top106 antenna. Cheap and effective.

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Compared to the helical or?

What do you say about this kind of antenna:

https://www.aliexpress.com/item/32891399821.html?spm=a2g0s.imconversation.0.0.28923e5fBh3sYd&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.177931.0&scm_id=1007.13338.177931.0&scm-url=1007.13338.177931.0&pvid=5ea4b92d-cad3-4f95-9b5c-061661a08217&_t=gps-id:pcDetailBottomMoreOtherSeller,scm-url:1007.13338.177931.0,pvid:5ea4b92d-cad3-4f95-9b5c-061661a08217,tpp_buckets:668%232846%238109%231935&pdp_ext_f={"sceneId":"23416","sku_id":"65649347391"}

Yep

I have basically found this too, the helical are a little less accurate especially vertically but are more robust getting signal in less than perfect areas.

The flat patch style antennas are much more accurate all around but suffer keeping fix in tough areas compared to the helical.

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I also don’t recommend the helical antenna for surveying. It is very good in open space but not very good near trees or buildings. I have seen also false fixes if it struggles to fix. Generally if it fixes right away you can be sure that is correct fix. If it stays float for some time and then fix you should be careful. This principal is also for any brand receiver. I have used Sokkia,Spectra Precision based on novatel boards and now i am using e-survey gear with hemisphere board. They all have their weaknesses.
I want to ask if the new harxon style antennas are any good like the old Choke ring antennas.

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I’ve got the discontinued Harxon GPS 500 antenna (2) and paid about $275/each. They seem to have better, cleaner data. There’s nothing wrong with the helical s and they have good horizontal accuracy but not vertical in my opinion. If you’re not to worried about vertical, they’re light and good for open areas. Another problem is submitting to OPUS, you’ll have to use a “0” antenna height and then deal with the phase centers and ARP.

As for buying a cheap antenna, you get what you pay for. Regardless of the advertised info. For the M2’s, I’m satisfied with the static results with the Harxons. If anyone is considering replacing/using the helical, I would stick with an antenna cost of no more than the cost of the M2 and also make sure it’s in the calibrated antenna database for possible use in OPUS. Harxon has great products, but in my opinion the helical is for UAV use. My helicals are for backup only.

Using the Harxons for a static baseline for boundary work, I’m confident in the elevations after PP with the rover. I don’t really need vertical info for boundary work, but it’s good to have as we have been 3D surveying for years. It’s just as easy to determine elevations as it is not to. Also it’s one of many indicators of a bad fix either RTK or PP. It’s amazing with the LIDAR data in our state, we’ve seen accuracies of +/- 5cm just checking road intersections and other landmarks that haven’t been disturbed since the LIDAR data was flown.

Antennas are just a part of the process/instruments that help determine accuracy using GNSS signals.

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Hi @rsurveyor1,

Reach RS+ shouldn’t be much affected by multipath. Do you experience issues with getting a Fix? Maybe there are some other reasons? I could help.

Also, both workflows you described in the initial post look good. It seems you already know about all the difficulties, like placing Reach M2 on a survey pole. So, I can only share my experience and say that we use Reach M2 as an NTRIP base for our office tests, and it works pretty well.

Anyway, if some difficulties arise, we’ll solve them.