# REACH M2: Coordinates and precision

Newbie…With the values shown, do the 190mm & 170mm values suggest the total offset distance with respect to the mounted GPS antenna (manual coordinates were entered)? So, on each side of antenna, 1/2 of these values.

https://i.imgur.com/NSjxCFd.png

This is more a confidence interval than an actual offset.

The confidence interval is plus or minus this value, so 1/1 of these values on each side.

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In farming using WAAS, they say 6-8" pass to pass accuracy, and those two values represent 7.5" (190mm) and 6.7" (170mm). So I suspected a possible relationship if say driving N/S or E/W directions.

Thanks for tidbits.

DART BOARD ANALOGY

### Standard Deviation

• Analogy: Imagine you’re playing darts, and you throw 10 darts aiming for the bullseye (the center). After throwing all your darts, you measure how far each dart is from the bullseye.
• Explanation: Standard deviation is like looking at how spread out your darts are from the average position of all your darts. If your darts are all clustered tightly together, the standard deviation is low, meaning you are consistent in where you throw, even if you’re not hitting the bullseye.
• In GNSS: This tells you how precise your GNSS measurements are – how consistent your position estimates are around an average point.

### RMS (Root Mean Square)

• Analogy: Now, instead of just looking at how spread out the darts are, you calculate the average distance of each dart from the bullseye and take the square root of the average of these squared distances.
• Explanation: RMS is like measuring how far, on average, your darts land from the bullseye, considering both the average position and the spread of your darts. This gives a single number representing your overall accuracy.
• In GNSS: This combines both the average error (how far off your measurements are from the true position) and the variability (how spread out the errors are). It gives you a sense of the total error magnitude.

### Summarizing the Differences

• Standard Deviation: Measures how close your darts (positions) are to each other. It shows precision.
• RMS: Measures how far your darts (positions) are from the bullseye on average. It shows overall accuracy.

In simpler terms, standard deviation is about consistency in your throws, while RMS is about how close you actually get to the target.

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Exactly @timd1971 !

That’s why I always insist on longer observation times !

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Using Average single position for 30 minutes
OPUS: OVERALL RMS: 0.018(m)

But, ND DEPT OF TRANSPORTATION SURVEYS & PHOTOGRAMMETRY
DATE: DECEMBER, 2006 says for OPUS:

1. Use 95% or more of your observations.
2. Fixed at least 95% of the fixed ambiguities.
3. Overall RMS should seldom exceed 1.5cm (0.015m). Maximum 1.8cm (0.018m).
4. The peak-to-peak errors should seldom exceed 3cm (0.030m). Maximum 4cm (0.040m).
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I’ve used this a few times due to problems with u_blox-rinex conversion routines for use in Javad Justin 3 PP software:

I haven’t had any issues in post-processing or use of NGS OPUS since using “rtools”.

I seldom use OPUS much, it’s more of a verifying tool when I’m post-processing in JJ3.

FWIW: I was puzzled why CORS use 10 digits, and Emlid 8

How Many Decimal Digits for Storing Longitude and Latitude?

Summary: 7 digits are sufficient to store coordinates with centimeter accuracy and 8 digits are enough to store coordinates with millimeter accuracy. Additional digits right of the decimal point will lead to micrometer or nanometer accuracy, which is not relevant in most geospatial applications.

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Hi guys,

Thank you for the meaningful conversation!

@phainein7, from my side, I only wanted to note that, as I understand from the screenshot, you didn’t have a FIX solution. Are your results sufficiently accurate? If you’d like to improve it, I can help you with possible options.

Just exploring this topic, and wanted to get a handle on the accuracy side. By Googling around, I found some tidbits that assisted in understanding this topic, for instances,

One network station in Australia details its GPS accuracy. Here is this station’s details.

There are sinkholes in Louisiana, and here are the OPUS results for their CORS quality equipment installed in 2013. Here is the overview of this project: CORS911: Real-Time Subsidence Monitoring of the Napoleonville Salt Dome Sinkhole Using GPS