Roughtly converting DOP to metric error

There is a rough indication of signal error sent down from each GPS
satellite - the URA or user range error. It is defined in IS-GPS-200D
available at http://www.navcen.uscg.gov/gps/geninfo/IS-GPS-200D.pdf.
Here's the text describing it:

6.2.1 User Range Accuracy. User range accuracy (URA) is a
statistical indicator of the ranging accuracies
obtainable with a specific SV. URA is a one-sigma estimate of the
user range errors in the navigation data for the
transmitting satellite. It includes all errors for which the Space
and Control Segments are responsible. It does not
include any errors introduced in the user set or the transmission
media. While the URA may vary over a given
subframe fit interval, the URA index (N) reported in the NAV message
corresponds to the maximum value of URA
anticipated over the fit interval.

Currently the URA's smallest value is zero, meaning there is a one-
sigma range error estimate for that fit interval between 0 and 2.4
meters. The URA values increase from there.
When CNAV data begins transmission, the URA will have a different
meaning, and can take on negative values. This gives a much better
precision to the URA estimates. CNAV data will be available on the
new L2C signal.
Ted

In fact they should not report error in position, but an estimate of
the error.
If the signal is good, residuals are low, dop is good (and other
If the signal is low, residuals are very big, dop is bad (and other
And you can mix all the situations like bad signal with good
dop... :)
A complex formula is used for the estimation.
Anyway, GPS receivers that usually have a message for the error
estimation tends to be too much optimistics :)

DOP only includes satellite geometry (not signal strength).

dop... :)

But may be you knew that.

Rigth. DOP only includes satellite geometry. That's why I say that
can't be used for error estimation (at least, not in a reliable
way! :) ) but you need to consider other parameters.
Anything in my post that let think something else?
Maybe I missed something in my examples of error estimation...

Rigtht. DOP only includes satellite geometry. That's why I say that
can't be used for error estimation (at least, not in a reliable
way! :) ) but you need to consider other parameters.
Anything in my post that let think something else?
Maybe I missed something in my examples of error estimation...

Someone could read your orignal wording as saying that good signal is a
requirement for good DOP but good signals from each satellite (as you are
aware) is not a contributor to good DOP as it only based on the geomentry
not the quality of the signal.