[Student Question] Understanding .pos Files

Hello, I have a basic question about understanding the .pos files created from my base station’s static observation data. There are several columns in the table, and I can’t find anywhere that explains what each of them means. Some I understand, but others I don’t:

GPST: GPS time (equivalent to UTC?)
latitude(deg): latitude
longitude(deg): longitude
height(m): height (orthometric or ellipsoidal?)
Q: ?
ns: number of satellites (?)
sdn(m): ?
sde(m): ?
sdu(m): ?
sdne(m): ?
sdeu(m): ?
sdun(m): ?
age(s): age of the fix in seconds (?)
ratio: ?

Thanks in advance for the help.

Hey @brillonha , welcome to the forum.

Emlid Studio is based upon a program called RTKLib. Have a look at the RTKLib manual

Jump down to Appendix B File Formats, B.1 Positioning Solution File for some definitions.

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Hi @brillonha,

Welcome to our community!

The manual mentioned by Dave provides a thorough explanation of the values; however, I noticed some uncertainty in your message that requires some additional clarification. Let me explain them.

GPST: GPS time (equivalent to UTC?)

The GPST and UTC are really close to each other but not exactly the same. The difference between UTC and GPS time is that UTC is adjusted periodically to account for the earth’s irregular rotation, using a process called leap seconds. Leap seconds are added to UTC periodically to keep it in sync with the earth’s rotation. GPS time, however, does not account for leap seconds, meaning there is a constant offset between GPS time and UTC. At the moment, the offset of UTC to GPS is +18 sec.

height(m): height (orthometric or ellipsoidal?)

After processing in Emlid Studio, you get the data in the same datum as the coordinates of the base. As a result, the ellipsoid of this datum is used to calculate the height value.

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