your position is our focus
4.1.3 Dynamic Platform Model
The
LEA-4R/TIM-4R
only
supports
the
Automotive
Platform.
4.1.4 Static Hold Mode
Do
not
use
this
mode
with
the
LEA-4R/TIM-4R
4.1.5 Degraded
Navigation
Degraded
navigation
describes
all
navigation
modes,
which
use
less
than
4
satellites.
4.1.5.1 2D
Navigation
If
the
GPS
receiver
only
has
3
satellites
to
calculate
a
position,
the
navigation
algorithm
uses
a
constant
altitude
to
make
up
for
the
missing
fourth
satellite.
When
losing
a
satellite
after
a
successful
3D
fix
(min.
4
SV
available),
the
altitude
is
kept
constant
to
the
last
known
altitude.
This
is
called
a
2D
fix.
!
Note
The
ANTARIS
®
4
GPS
Technology
does
not
calculate
any
solution
with
a
number
of
SVs
less
than
3
SV.
Only
ANTARIS
®
4
Timing
Receivers
can
calculate
timing
solution
with
only
one
SV.
!
Note
If
the
receiver
makes
initial
2D
LSQ
fixes
during
acquisition,
the
initial
altitude
is
set
to
500m.
To
change
the
initial
altitude
use
UBX
–
CFG
(Config)
-
NAV2
(Navigation
2)
message.
4.1.5.2
Dead Reckoning/ extrapolating positioning
The
implemented
extrapolation
algorithm
kicks
in
as
soon
as
the
receiver
does
no
longer
achieve
a
position
fix
with
a
sufficient
position
accuracy
or
DOP
value
(can
be
configured
in
UBX-CFG-NAV2).
It
keeps
a
fix
track
(heading
is
equal
to
the
last
calculated
heading)
until
the
Dead
Reckoning
Timeout
is
reached.
The
position
is
extrapolated
but
it’s
indicated
as
“NoFix”
(except
for
NMEA
V2.1).
!
Note
For
sensor
based
Dead
Reckoning
GPS
solutions,
u-blox
offers
Dead
Reckoning
enabled
GPS
modules
(LEA-4R/TIM-4R).
It
allows
high
accuracy
position
solutions
for
automotive
applications
at
places
with
poor
or
no
GPS
coverage.
This
technology
relies
on
additional
inputs
from
a
turn
rate
sensor
(gyro)
and
a
speed
sensor
(odometer
or
wheel
tick).
4.1.6 Almanac
Navigation
The
satellite
orbit
information
retrieved
from
an
almanac
is
much
less
accurate
than
the
information
retrieved
from
the
ephemeris.
If
during
a
startup
period,
only
almanac
information
is
available,
(e.g.
while
the
ephemeris
still
is
being
downloaded)
the
receiver
still
is
able
to
navigate
based
on
almanac
orbits.
With
almanac
navigation
enabled,
when
a
new
satellite
rises
and
its
reception
just
has
started,
the
receiver
might
use
an
almanac
to
use
this
satellite
in
the
navigation
solution
until
the
ephemeris
is
fully
retrieved.
By
disabling
almanac
navigation,
the
receiver
does
not
use
the
almanac
for
navigation,
but
will
always
wait
to
collect
the
entire
ephemeris
information
before
including
a
satellite
in
the
navigation
solution.
With
an
almanac
only
solution
the
position
will
only
have
an
accuracy
of
a
few
kilometers.
Normal
GPS
performance
requires
at
least
4
satellites
included
in
the
navigation
solution,
which
have
ephemeris
information
available.
Almanac
navigation
allows
much
faster
start
up,
as
there
is
no
need
to
wait
for
the
completion
of
the
ephemeris
download
(>18s).
This
is
useful
whenever
an
inaccurate
position
is
better
than
no
position
(e.g.
emergency
or
security
devices).
LEA-4R
/
TIM-4R
-
System
Integration
Manual
/
Reference
Design
Navigation
GPS.G4-MS4-05043
Page 26