SEPTENTRIO PolaRx5TR, Reference Manual

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4 SBF Reference
DOP
Number: 4001
"OnChange"
interval: default PVT output rate (see 4.1.8)
This block contains both Dilution of Precision (DOP) values and SBAS protection levels. The
DOP values result from a trace of the unit position variance-covariance matrices:
Position Dilution of Precision:
PDOP =
p
Q
xx
+ Q
yy
+ Q
zz
Time Dilution of Precision:
TDOP =
p
Q
bb
Horizontal Dilution of Precision:
HDOP =
p
Q
λλ
+ Q
ϕϕ
Vertical Dilution of Precision: VDOP =
p
Q
hh
In these equations, the matrix
Q
is the inverse of the unweighted normal matrix used for
the computation of the position. The normal matrix equals the product of the geometry
matrix A with its transpose (
A
t
A
). The term "unweighted" implies that the DOP factor only
addresses the effect of the geometric factors on the quality of the position.
The DOP values can be used to interpret the current constellation geometry. This is
an important parameter for the quality of the position fix: the DOP parameter is the
propagation factor of the pseudorange variance. For example, if an error of 5 m is present
in the pseudorange, it will propagate into the horizontal plane with a factor expressed by
the HDOP. Hence a low DOP value indicates that the satellites used for the position fix result
in a low multiplication of the systematic ranging errors. A value of six (6) for the PDOP is
generally considered as the maximum value allowed for an acceptable position computation.
The horizontal and vertical protection levels (HPL and VPL) indicate the integrity of the
computed horizontal and vertical position components as per the DO 229 specification.
In SBAS-aided PVT mode (see the
Mode
field of the
PVTCartesian
SBF block), HPL and
VPL are based upon the error estimates provided by SBAS. Otherwise they are based upon
internal position-mode dependent error estimates.
Parameter Type Units Do-Not-Use Description
Sync1
c1
Block Header, see 4.1.1
Sync2
c1
CRC
u2
ID
u2
Length
u2
1
byte
TOW
u4
0.001
s
4294967295
Receiver time stamp, see 4.1.3
WNc
u2
1
week
65535
NrSV
u1
0
Total number of satellites used in the DOP computation, or 0 if the DOP
information is not available (in that case, the
xDOP
fields are all set to 0)
Reserved
u1 Reserved for future use, to be ignored by decoding software
PDOP
u2
0.01 0
If 0, PDOP not available, otherwise divide by 100 to obtain PDOP.
TDOP
u2
0.01 0
If 0, TDOP not available, otherwise divide by 100 to obtain TDOP.
HDOP
u2
0.01 0
If 0, HDOP not available, otherwise divide by 100 to obtain HDOP.
VDOP
u2
0.01 0
If 0, VDOP not available, otherwise divide by 100 to obtain VDOP.
HPL
f4
1
m
−
2
·
10
10
Horizontal Protection Level (see the DO 229 standard).
VPL
f4
1
m
− 2
·
10
10 Vertical Protection Level (see the DO 229 standard).
Padding
u1[..] Padding bytes, see 4.1.5
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