I’m experienced with GIS but am new to learning about RTK and GNSS in general. I’m a soil scientist working in Saskatchewan, Canada. I need to be able to visit predetermined (but unmarked) points in the field with ~1 m accuracy. I will be mostly on foot at the sites. I think the EOS Arrow 100 with its concurrent multi-constellation use and real-time SBAS corrections would be well suited to this work. But I became aware of the Reach RS+, which is very reasonably priced – 2 units is cheaper than one of the EOS Arrow 100 units. Would I be able to achieve similar accuracy with one or two Reach RS+ units – without a known location for the base? I will be visiting many sites – none of which I will have known coordinates for the base. I know the Reach RS+ uses SBAS, but as far as I understand, it requires post-processing, which would not inform me locating the predetermined sample points while in the field. I am not very familiar with the RTK network in Canada – it looks fairly sparse in Saskatchewan https://webapp.geod.nrcan.gc.ca/geod/data-donnees/rtk.php?locale=en and subscription fees are likely not feasible.
Can the Reach RS+ work as a field GNSS unit for my purposes? Beyond the price difference, there’s also the potential in the future that we would be doing some UAV work, which the Reach could be used for.
Do you require relative or absolute accuracy? Relative accuracy is maintaining that all they points are in relation to each other on their own as designed and absolute accuracy is the the design is precisely located geographically in relation to the rest of the world.
The accuracy that you can achieve with the Reach units is centimeter level whereas the Arrow 100 is marketed as “submeter”. It may be ok for GIS, so it is really up to you what you are ok with.
When you say the points are predetermined, how are they derived? The Reach units do have the capability of running RTK between a standalone base station and rover without the need for an external service. If you can define a known point for the base (using a GIS map or other submeter data) then you will be submeter absolutely, but your points should be centimeter in relativity.
Thanks for your response.
I would require absolute geographic accuracy. The points are generated using a conditioned Latin hypercube sampling design. This is used for predictive soil modeling work. It’s important that the predetermined points are sampled somewhat accurately - submeter to about 1m accuracy is appropriate. Centimeter accuracy is overkill for these purposes, because the spatial resolution of the modeling is about 1 to 2 m^2. Coarser than 1m absolute accuracy becomes less ideal.
The problem is I will not be able to establish a known point for the base. So I’m assuming that without use of a RTK network, and without real-time SBAS processing, one or two Reach RS+ units would likely only achieve absolute accuracy of > 2 meters by using GPS, Glonass, etc.
That’s a tough decision. I will say that from my experience the Reach RS+ receivers are limited compared to allot of other devices out there, but the price suggests what you should expect and if you are within 1,000ft of the base then they work well. The L1-only nature has been discussed with having issues maintaining a fix, but I have still been able to achieve submeter accuracy in a float condition so I consider them GIS devices. If you let the base station acquire a point for 30 minutes you will be absolutely accurate.
From what I read the Arrow 100 is L1-only as well which is why they probably market submeter. One thing to remember about a submeter device is that every point shot has a potential error of 60-70cm as they market it. This means that not only would you be a little off absolutely, but each point would be in that tolerance so your relativity would suffer as well.
The RS2 would be a much better piece of equipment (what I would consider survey grade) and would put you in a better position for future UAV use, but it also sounds like that the Arrow 100 would suffice the need for now. I have seen the Arrow 100 for $3k? The Reach RS2 survey kit is $3800. Then you have to look at accessories. I don’t believe the Arrow comes with an external antenna?
I think the Arrow does come with one antenna https://eos-gnss.com/product/gnss-accessories/eos-antennas which is only L1.
When you say you are able to achieve absolute accuracy by letting the base station acquire a point for 30 minutes, do you mean when that base station is placed at a known location, or at a new/unknown location? And is there any assessment of its absolute accuracy provided to you by the device?
If you need to get centimeter-level precision in RTK you will need both rover and a base. Or you can use NTRIP service and use only a rover.
Since you don’t want to involve NTRIP and you won’t have an absolute reference point on site you can use PPP. You will need to log a position with a base at a new site for about 2 hours and then send the raw data to NRCAN CSRS-PPP service. This will provide you with an absolute base’s position.
Also, you need to consider the surroundings where you are going to carry out your surveys before choosing the receiver. Single-band Reach RS+ can hardly work in the areas where the sky view is obstructed by trees or buildings. In that case, it is better to use multi-band Reach RS2. You can check this article regarding the selection.
If in the future you are going to do UAV mapping you can check our Reach M+ and Reach M2 receivers specially designed for use onboard the drones.
Thanks for the response! That’s helped me make sense of things.
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