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Collecting Data for NGS  

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Field Dog
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This Monday I will get my first experience with static GPS. I will occupy an NGS point for at least 4:10:00, the boss
likes a ten minute buffer, then move on to another point. The data will be used by NGS for the 2022 datum. The boss
showed me the logging data from a short static session he ran at the office. Does anyone have a description of what all
the data means?

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NGS
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Jim Frame
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John Putnam
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If you viewed the file itself in a text viewer then I would say you were looking at RINEX file.

NGS requires The Receiver Independent Exchange Format (RINEX) files.  Depending on how your receiver collects data, each occupation set creates at 3 files (The observation data file , the navigation message file and the Meteorological data file).

The observation file header contains the basic information about the setup (antenna type & height, time, point name etc.).  The main body of the file grouped by individual observation and contains information collected from each satellite.

Wiki has a link to the IGS documentation on the RINEX format if you want to really delve into it.

 

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GeeOddMike
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@john-putnam

To spare the OP the need to search, here is a presentation including RINEX file samples:

 

the RINEX file format is completely described here:

there is also a later version 3.0.

 

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jalbrz
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@john-putnam

FYI, OPUS does not require a RINEX upload.  Whenever you do upload a non-RINEX file to OPUS, the first step within the OPUS "engine" is that it converts your raw file to RINEX using TEQC.

For example, Topcon .tps files will upload directly to OPUS.  I think the the Trimble .dat files will also direct upload to OPUS, but I don't have one on-hand to double-check right now.  I can say that it will not accept Trimble .T02 or the new .T04 files, users need to convert to RINEX, and I highly recommend using ConvertToRINEX to do that.  For that matter, I recommend to always use the manufacturer's provided software to convert their raw files.

 

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Take the next step in your career, PPI will get you there

Paul in PA
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Sounds like you are very new at GPS. Things you want to make sure you have recorded, most of which should be in the RINEX file.

Site IPD number, Receiver type and serial number, antenna type and serial number, antenna height to ARP (Antenna Reference Point), Company name.

Record the antenna height twice at the beginning and twice at the end of the observation. Measure in feet and remeasure in meters, do not measure in one and convert to other. You can add information on the "comment" lines. The RINEX file should automatically include the RINEX converter type and RINEX file type.

Of interest in the data for basic GPS, the L1 and L2 are wave length specific information and are dependent on the receiver algorithms. i.e. two different receivers can give two different values for the exact same signal.

C1, P1, C2 or P2 are actual metric measurements from the satellite antenna to the receiver antenna, (20,000,000m to 24,000,000m typical)(a value like 19,730,000m means the satellite is almost directly overhead). They vary because the speed of light varies with the signal wave length and varies in different directions from the receiver antenna due to atmospheric conditions. C1 varies from P1 because of algorithmic differences, etc.

D1 and D2 are Doppler differences and the sign varies whether the satellite is approaching or departing from an overhead position.

The L1 and L2 values are to 3 decimal points and the 4th and 5th digits after the decimal point refer to other values of the quality of that signal. L1 is geater than L2 by a factor of 1.283333, the difference in wavelength. If you divide L1 by L2 and get a value near 1.283+/- that tells you the receiver is calculating the observations independently. Some receivers base both values on a intertwined calculation and the differences can be in the order of 1.2833xx to 1.2833yy.

Every epoch of data is preceded by the Julian date and GPS time of the signal, the number of satellites reported and the satellite PRN numbers in order of data, plus there is number included as to the number of GPS seconds added to the UTC clock.

A RINEX file from any manufacturers receiver can be used with any manufacturers post processing software, hence the term RINEX, Receiver INdependent EXchange format.

That is the quick version.

Paul in PA

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Bill93
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Posted by: @paul-in-pa

Site IPD number, Receiver type and serial number, antenna type and serial number, antenna height to ARP (Antenna Reference Point), Company name.

Typo: that's PID, the NGS unique 2-letter plus 4-digit identifier for each disk or other mark in their data base.

It's good to have all that info Paul listed, but the only items on that list you submit to OPUS besides the file are antenna type and height of the Anrenna Reference Point (ARP) above the mark. Those are critical to getting good results.

If you are curious about the RINEX contents, you may learn something, but that is not necessary to do the job.  There are better things to study about GNSS, particularly how to identify locations that have bad multipath.

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Mark Mayer
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Posted by: @field-dog

Does anyone have a description of what all
the data means?

It means that you are going to have 4 hrs and 10 minutes of free time on your hands. Bring some reading material.

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Jitterboogie
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@mark-mayer

....and be glad this isn't the Mojave desert in July.........  😛

 

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Larry Scott
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@jitterboogie

Or back in the day when there only 4-5 hrs of satellite availability: night in winter, day in summer. 5 channel, L1, and car batteries. 

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