Thread: Accuracy figure of horizontal position fix on GPSMAP 66 satellite screen?

Originally Posted by Magnetron

have a read of this

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Thank you Magnetron for that link. It was quite interesting to read.

Originally Posted by Magnetron

and with SA of 4mtrs and WGA84 1.8mts out you are now upto 5.8mtrs away from true coordinate on the ground.

To be technically correct, you are actually 'up to 5.8 meters away from the position on the Earths surface that used to reside at the specified location.'

You said it yourself:

Originally Posted by Magnetron

Since WGA1994 Australia has moved 1.8mts West so now the new maps needed to be coordinated to GDA2020.

The Maps need to be updated to reference the new ground location for the specified coordinates.

Had you and your GPSr been able to remain just above any chosen landmark in Austrailia without moving for the entire duration of time required for the continent of Austrailia to drift those 1.8 meters, your GPSr would still be reporting the same coordinates (because you never moved) while the landmark below you would now be 1.8 meters farther away!

This is not a failure of the GPSr accuracy, but rather an effect of the always moving surface of the Earth.

As you stated,

Originally Posted by Magnetron

so now the new maps needed to be coordinated to GDA2020.

The maps must be updated to correctly show the new location of the chosen landmark.

The GPSr is always showing your 'True' location, even when the (outdated) map you are using does not agree.