ates from the true position, by less than the standard deviation. This probabil-
ity is not enough for a reliable quality indicator.
This unreliability is true for low redundancy situations such as a constellation
of four satellites. In such a case, the RMS converges to zero and the standard
deviation would show an unrealistically small value.
Computation
GS measurements
Least square
adjustment
Unknowns
like rover
coordinates
Root Mean Square RMS
= a posteriori of unit weight
•
Reflects all error sources
such as diffraction, multi-
path, ionospheric and tropo-
spheric disturbances.
•
Indicator of the measure-
ment noise and environmen-
tal conditions.
Elements of cofactor matrix
•
Reflects the influence of the
different constellations of the
satellites on the coordinate
components.
Standard
deviation
Empirical
assumptions
Coordinate Quality CQ
Range
For a phase fixed
solution
Centimetre level
For a code solution
From 0.4 m to 5 m.
Position CQ versus height CQ
All GS computed positions are almost twice as accurate in plan than in height.
For the position determination, satellites can appear in all four quadrants. For
the height determination, satellites can appear in two quadrants. Fewer quad-
rants weaken the height position compared to the plan position.
1042
Glossary
