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GNSS measurement precisions

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5 Users
Posts: 114
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I was scrolling through the measurement settings and noticed the measurement precisions from the manufacturer seemed high to me. Does anyone change the factory settings or do they leave them as is? What is a normal precision setting for measurements?

Posted : January 19, 2023 9:06 pm
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Yes, I adjust them frequently based on my needs at the time.  Usually I set them in Trimble Access based on the class survey I'm performing.  Class A horizontal is 0.1' in NC, B=0.12', C=0.15'.  If I'm performing GIS location of assets, I set it to 3.2' and open the vertical way up.  Recently, I've just been keeping the factory settings and handling outliers in TBC.

Go by the standards in your state.  

Posted : January 20, 2023 6:08 am
Norm Miller
Posts: 1095
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I always had our crews have the default higher than the desired. Remember, the actual precision for every observation is available real time or in the data. You can dial it down to zero if you want. Might make it kind of hard to get anything done. Keeping the default high should help you avoid the temptation to let the machine run you vs. letting you run the machine by keeping an eye on the real time things such as DOP, # SVs, V prcision, H precision, etc. While we are on the subject, please save your data files and have a way to review them with a generic text editor and not just save the coordinates only without any other observation information. I used to see people falling into this trap with RTK. 

Posted : January 20, 2023 6:34 am

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Keep in mind the default Trimble access setting is for 1-sigma, aka 0.67 confidence and not 95% confidence. 0.1 at 67% is a but higher at 95% setting. And these are predicted precisions. You can observe 2 points at 0.03 H precision, but the distance between them via a total station could be 0.1’ off of the GNSS value inverse. 

It’s good to understand the data and not just change settings in software since GNSS data isn’t the same quality as total station.

Posted : January 25, 2023 6:14 am
Posts: 1621
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If you are working in Access there is also a 'cadastral tolerances' function.

It is useful for more than just for cadastral work.

You can use it for configurable display and report on the controller.

I find the summary display particularly useful.

It works in addition to, and across both, the GNSS and TotalStation measurement checks.

The  Access help file has details on how it works and how to configure it.

Posted : January 25, 2023 12:01 pm