Dead Reckoning

Dead reckoning (DR) uses inertial measurement unit (IMU) data to estimate position when GNSS signals are unavailable — in tunnels, parking garages, and dense urban canyons.

Supported Variants

Variant	DR	RTK	Sensor Inputs
LC29H(BA)	Yes	Yes	IMU, wheel tick, CAN bus
LC29H(CA)	Yes	No	IMU, wheel tick

The BA variant combines DR with RTK for centimeter-level positioning that persists through GNSS outages. The CA variant provides DR-only — maintaining position continuity without RTK corrections.

DR Mode Configuration

Set the positioning mode via PQTMCFGDRMODE:

$PQTMCFGDRMODE,W,2*CS

Mode	Description
0	GNSS only — inertial sensors ignored
1	DR only — GNSS signals ignored
2	GNSS+DR auto (recommended) — fuses both sources

Mode 2 seamlessly transitions between GNSS and DR as signal conditions change.

Wheel Tick Configuration

External wheel tick (odometer pulse) input improves DR accuracy by providing ground-truth speed:

$PQTMCFGWHEELTICK,W,1,20,2.0000*CS

Parameter	Description
enabled	0 = disabled, 1 = enabled
ticks_per_rev	Pulses per wheel revolution
circumference	Wheel circumference in meters

Tip

Wheel tick data significantly improves DR accuracy, especially during extended GNSS outages. Even approximate values for ticks-per-revolution and circumference help — the module self-calibrates during normal driving.

CAN Bus Setup (BA Only)

The LC29H(BA) can read vehicle speed and wheel tick data directly from the CAN bus:

$PQTMCFGCAN,W,1,500000*CS        Enable CAN at 500 kbaud
$PQTMCFGCANFILTER,W,0,0x123,0x7FF*CS   Filter for specific message ID

Vehicle DBC (CAN database) mapping defines how to extract speed and direction signals from CAN frames:

$PQTMCFGVEHDBC,W,<dbc_config>*CS

Calibration

1. Initial calibration drive — After power-on, drive normally with good GNSS signal for 5–10 minutes. The module auto-calibrates its IMU during this period.

2. Drive patterns — Include straight-line segments, turns, and stops for comprehensive IMU alignment.

3. Verify calibration — Enable extended INS status to monitor calibration progress:

   $PQTMCFGEINSMSG,W,1*CS

4. Save parameters — Once calibrated, save to persist across power cycles:

   $PQTMSAVEPAR*5A

Performance Factors

Factor	Impact
Calibration quality	Most important — drive with GNSS before entering tunnels
Wheel tick input	Major improvement for extended outages
Vehicle type	Cars and trucks calibrate better than bicycles
Outage duration	DR accuracy degrades over time (~1–2% of distance traveled)
Temperature stability	IMU drift increases with rapid temperature changes