What Is the Epoch Time for the WGS84 Coordinate System?

[mjdiaz89]

Hello,

I've been searching all over for the epoch time of the WGS84 coord system. A GPS I'm using says its 06/01/1980, but I don't know if starts from 12:00:00 ET. Is there an epoch by definition or is it arbitrary?

 

[mgb_phys]

There isn't a precise epoch for the coordinate system - the 1984 is just when the data was agreed. There are slight real changes to the values with time, but the real changes come with more accurate measurements.

There is a start epoch to the GPS clock data but that's just a software detail, GPS time doesn't include leap seconds - so GPS and UTC were synced in 1980 but GPS now lags by a number of seconds.

 

[mjdiaz89]

Interesting that there isn't a defined epoch, only a synced time. Yes, I believe the lag is 13 seconds.

Thank you very much :)

 

[mgb_phys]

Yes, astronomical coords need a definite epoch because the star positions are moving.
Although the Earth's shape really changed between say Airy 1837 and WGS84 it's insignificant compared to the change in the measurement accuracy.

Just to confuse things further - most GPS receivers do give UTC, the number of leap seconds is sent to the satellites as part of their update data.

 

[DeeNos]

Hello,

Thank you for your question. The WGS84 coordinate system does indeed have an epoch time, which is used as the reference time for all measurements. The epoch time for WGS84 is January 6, 1980 at 00:00:00 UTC (Coordinated Universal Time). This is equivalent to January 5, 1980 at 19:00:00 ET (Eastern Time).

This time was chosen as the starting point for WGS84 because it was the date when the first GPS satellite was launched and began transmitting signals. This allowed for a consistent and accurate reference point for all GPS measurements.

It is important to note that the epoch time for WGS84 is not arbitrary and is defined by the International Earth Rotation and Reference Systems Service (IERS). This ensures that all measurements using the WGS84 coordinate system are standardized and accurate.

I hope this helps clarify the epoch time for WGS84. Let me know if you have any further questions. Best of luck with your research!

Sincerely,