Chicken and the egg.. Known and Unknown points?

It really depends on what end product the user is trying to make. In your case, you’re working on projects where relative elevations are critical and vertical centimeters/millimeters matter. So I guess your perspective reflects that reality.

For some of the graduate students at my uni that work on projects where they are simply doing ground truth measurements to compare with satellite sensor data, a lot of the time they could maybe get away with single solutions on a multi-freq receiver as only the XY is important. As long as the positions precisions fit inside the spatial resolution of the imagery, they’re fine.

But other students have more specific needs and in the case of those specialized snow and ice studies, some are measuring the snow depth with radar units strapped to a snowmobile with a GNSS pole. These guys need really good vertical accuracy to get meaningful snow depth measurements. They have to work either in RTK (no RTN in the arctic) or PP their data, but the absolute vertical works fine with stock datums.

And if we’re talking about legal surveying (although I’m not talking from deep expertise here), from what I’ve seen it’s only the XY that is critical to defining lot boundaries so the ellipsoid/geoid discrepancy issues become less important.

For my personal projects where I do medium scale cartography, even sub-meter precision is good enough but if I’m doing orographic research and need to differentiate summits, then Z is the more critical measurement and I don’t even care about XY that much. I’ll PP those with long static observations.

Definitely different worlds then. I have never seen a GIS, Topographic Survey or Construction project where centimeter-level accuracy of YX is not required. In some cases it could be as far out as a decimeter, but never beyond that.

Either your work is site relative and absolute Lat and Lon is not needed, you are working on a grid coordinate system where YX is required and with localization Lat and Lon is not or as you said you are just needing sub-meter. In my experience you cannot acquire sub-meter with averaging even though the rover is corrected via RTK.

As for stamped survey you are correct on metes and bounds and land title surveys, but topographic surveys always require two local benchmarks with centimeter accuracy in YXZ and logging in our experience.

Hi Michael,

Let me clarify this.

Reach RS+ is a single-band receiver. It’s capable of obtaining centimeter-level accuracy if you’re using it in RTK and PPK. This ultimately implies that another receiver is necessary whether it’s a remote NTRIP station or the local base station.

If you don’t need absolute centimeter-level accuracy for your survey, you can set up your Reach RS+ receiver as a base on an unknown point by averaging the position in a Single solution. The absolute accuracy of the position you’re going to get is about a few meters. If you set up a multi-band Reach RS2 in a standalone mode, you will get the same accuracy of a few meters.

If you need to establish a coordinate of an unknown point with absolute centimeter-level accuracy in an area without Internet access, you can use the PPP services as other users have mentioned. We have a detailed guide on it.

The majority of the services do in fact work with multi-frequency logs to have more data for analysis. With a single-band receiver, you can work with NRCAN service. It’s possible to get the accuracy of up to 15-30 cm with it as our user’s test suggests.

Let me repeat that Reach RS+ and Reach RS2 are capable of obtaining the same centimeter-level accuracy while working in RTK and PPK. These receivers are designed to be used in different conditions. Reach RS2, as a multi-band receiver, allows you to survey in somewhat complicated environments like urban areas or under light foliage. You can also reach longer baselines and obtain Fix in RTK faster.

Reach RS+ can be used in an open area with a clear sky view and in RTK it usually takes a couple of minutes to achieve a Fix solution. These are the characteristics and requirements for any single-band receiver.

It’s up to you to assess your environment and requirements of your workflow to decide which of the receivers is more suitable for you. For surveying in a somewhat difficult environment, it might be a good idea to consider Reach RS2.

I’d also suggest taking a look at our Placing the base guide where we described the most common scenarios of placing local base station with our receivers.

I hope this clears up the topic a bit.



Thanks for sharing your surveying workflows! Knowing how you usually work with our receivers is fascinating. Broadens our horizons :slight_smile:


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