Specifications

46 Z-Family Technical Reference Manual

c. Fixed solution, formal reliability = 99% (default)

d. Fixed solution, formal reliability = 99.9%

The command $PASHS,CPD,AFP controls the ambiguity fix parameter.

The four choices of formal reliability for fixed solution are provided to allow you to

trade off speed with reliability. The AFP setting controls the internal thresholds of the

receiver so that the expected statistical reliability of getting correctly fixed integers is

90%, 95%, 99%, or 99.9% respectively. The receiver fixes integers faster with

AFP=99 than with AFP=99.9.While the receiver is busy fixing integers, it gives a

float solution.

Operation under trees, or in other areas with frequent blockage of satellites signals

will lead to significantly degraded results.

Monitoring Accuracy

Besides fixed/float status, position accuracy is the most important consideration when

using the receiver for real time carrier phase positioning. The primary means of

monitoring CPD “fixed” and CPD “float” accuracy is the RRE message (see NMEA

section for full description). The RRE gives an indication of the overall quality

(precision) of the CPD position by displaying the RMS value of the error of all the

range inputs to the position solution. The RRE message also gives a real-time

estimate of the actual error in the CPD position in horizontal error and vertical error.

The actual position error of the system will be less than the standard deviations

displayed in the RRE approximately 68% of the time. If you multiply the standard

deviations by 2, the result is a conservative estimate of actual accuracy about 95% of

the time.

The quality of the RRE estimates improve with increasing number of satellites. The

RRE estimates may be very unreliable with only 5 satellites in view. The horizontal

estimates are derived from:

GST estimates of latitude, longitude, and altitude accuracy automatically account for

DOP, SNR, and many other factors. These parameters are built into the GST estimate

already and do not have to be recomputed by the user.

Required Number of Satellites

The receiver requires five or more satellites to fix integers, following power on, or

obstruction and re-acquisition. If the solution is fixed with five or more satellites, and

the number of satellites falls below five but stays above three, the solution stays fixed

and accuracy remains at the centimeter-level. Positions are always three-dimensional

when in RTK mode. Two-dimensional positions, using previously calculated

altitudes, are not possible.

LatError()

LonError()