Reach Single solution accuracy

Hello,

I would like to user Reach without a base station and post processing. My goal is to have 1m accuracy, is that possible?

Thanks for the help!
Vester

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@vester_vester
Hello! Standalone accuracy of Reach is ~2.5m. If you have SBAS satellites in view it should be ~2.0m.
There’s no way to achieve better accuracy without real-time corrections or post-processing because that’s what Reach relies on.

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Thanks for your help. Now I know where I stand. I will look in to post processing.

Does anybody have any reliable data of how accurat a singel reach can get with post? with no other corrections

If by “post” you mean post processing corrections should be < 2cm.

Yes, post process.
Should yes, but do you have any data or experience that tells this?
This would be average position, average would never be exact location and for how long do you let reach collect data?

With a single Reach and a good source for live correction data, then maybe 10cm accuracy would be a reasonable assumption? I have no experience with that setup though.

How long to collect data is a good question. With the software we have right now, we don’t really know the quality of our data until we examine it afterwards. So how long to collect is based on experience and what you can see on the ReachView status page. I’ve been telling people minimum 10 minutes on a point, preferably 20 if you want to be sure that you got the point. Seeing a stable fix for a length of time gives you confidence in your result, but really, the occupation time should be way shorter than that, and it can be - like a matter of seconds. You can leave your point as soon as your screen says “fix,” but if you find out it was an erroneous fix or one of poor quality, then you may have to go back to capture the point again.

Soon, I think we will have a little more live information on the ReachView status page which will help with deciding our occupation time.

I was actually thinking of no live corrections. Single Reach all alone :wink:
Ntrip provider to far away, no nearby known reference point and i need to set/find an absolute in the midle of somewhere.
How to do this?

Anybody testet out these providers for postprocessing?
-Apps
-Auspos
-Csrs
-Scout
-Magicgnss
And some others but they need L2 too

I was thinking of logging for at day and compile a solution in post process with one of the above providers of correction data. Or am i way of here?

@TB_RTK You can’t post-process a single REACH “all alone”. That would be what @mikhail.avkhimenia said as standalone position, ~2-5m accuracy. When you post-process, you are always processing to another GPS receiver on a known point. Whether that be a point with a GPS already running on the monument (i.e. those providers you mentioned), or not. If you are in the U.S., you can take advantage of the CORS network. Your other option is to find an already know reference monument (typically an NGS monument) and setup a REACH in STATIC mode on that, then post-process to the point you want to set “in the middle of somewhere”. The REACH can get a cm accuracy position up to 10km away with ~10 minutes of RINEX data, depending on sky/satellite conditions. If you want to go farther than that, then you need much longer observation times (hours) or an L1/L2 receiver (if you want to achieve cm accuracy).

By the way @bide, you can get live correction data and have cm accuracy, so long as you are within ~10km of the base station you are getting corrections from. That accuracy will come almost instantaneously if you are receiving live correction data. The best way to verify that you got a “good” fix when in live correction (or RTK) is to observe each point twice and separate the observations by 30 minutes or more. For example, start at your first point and do an observation on each point, then repeat once you get to your last point to have the maximum separation possible. The NGS recommends a 1.5 hour separation time between observations to get a completely different satellite geometry. However, sometimes you don’t have that much time and any separation is better than none. Then it’s best to average your two resulting coordinates, so long as they agree within the tolerance based on baseline distance.

Hope that helps!

Best,
Steve

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@cczeets 10km is a limit for kinematic, in static mode it is possible to get fix on a longer baseline (one of our users reported good results on ~80km), may require a much longer stay time though.

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Are you sure?
When i read this , it sounds like i can get a more accurat solutions by submitting my single data to this site and get a more accurate solutions.

CSRS-PPP is an online application for GNSS data post-processing allowing users to compute higher accuracy positions from their raw observation data.

CSRS-PPP uses the precise GNSS satellite orbit ephemerides to produce corrected coordinates of a constant “absolute” accuracy no matter where you are on the globe, regardless of proximity to known base stations.

Users can submit RINEX observation data from single or dual-frequency receivers operating in static or kinematic mode over the Internet and recover enhanced positioning precisions in the Canadian Spatial Reference System (CSRS) and International Terrestrial Reference Frame (ITRF).

Link http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/10925

@TB_RTK Read down a little farther. It states “You could setup the base station ahead of time and collect raw GNSS data (anywhere from 2hrs to 24 hrs depending on the accuracy required).” So, as @mikhail.avkhimenia stated, you can get a fix on a longer than 10km baseline. But, you need a much longer setup. They are stating 2-24 hours of data.

Thanks @mikhail.avkhimenia! I should have been more clear. Yes, you can get a fix on much longer baselines, with much longer observation times. And using post-processing.

Best,
Steve

Ok, so if time is no issue and i leave my reach out and log for 20hours, this would be possible?
I really need this in with a tiny spoon :yum:

@TB_RTK Yes. But, make sure you perform two (or three) separate observations with a decent separation time between them to verify the repeatable accuracy of your fixed coordinates!

Good luck and report back how it turns out!

Best,
Steve

All right, thats all for now. Thank you

Based on the above comments, one might ask, “what is the difference between a 20 hour observation and 3 separate observations over a 20 hour period?”

I think 3 separate initializations is better then one initialization. Please clarify if that means we should:

  • power off / power on the GPS(s) three times
  • click the start/stop button in ReachView for three separate logs
  • if post-processing, using 3 different time slices from one long observation

@bide All of my comments are applicable to post-processing. What that being said, there is a lot of difference. It depends on what accuracy you are trying to achieve and how long is your baseline. For a very long baseline, you may need two 20-hour observations.
The purpose of separate initializations is to verify the repeatable accuracy or increase the coordinate accuracy. GPS measurements are always +/- by a certain distance based on baseline length. The +/- difference is in a 3-dimensional coordinate (or, to simplify, a bubble). So, the more times you repeat an observation, the more accurate coordinate you get. If you perform separate initializations and separate those by an hour (for example), you get a different satellite geometry. This will also increase the accuracy of your coordinate, by averaging those two positions together. Or, it could just be a check to make sure you achieved a good fix and not a bad fix. Usually, this is only needed for longer than 10km baselines. Unless you are trying to get mm positional accuracy.
Powering off/on the GPS or clicking start/stop will do the same thing (create separate logs). However, you should separate your initializations by 30 minutes or more to get a different satellite geometry if you are looking to increase accuracy. Not just stopping and starting immediately after the next. The only purpose to stopping and starting immediately after would be to collect a separate observation to verify a good fix vs a bad fix.
I don’t quite understand your last question “if post-processing, using 3 different time slices from one long observation”?

-Steve

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Thanks for the explanation.

Where I was trying to go with my question was: Is there any benefit to stopping and starting the hardware (GPS chip) to force the chip to initialize? i.e. by power-cycling the device

Or is the ‘initialization’ we speak of purely in the post-processing software?

@bide Yes, a separate initialization (or observation) should be done by powering down the hardware.
You will have to post-process each observation separately in RTKLIB

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