APX-15 UAV GNSS-inertial navigation module

The Trimble APX-15 UAV is an inertial and satellite navigation module made by Applanix, a Trimble company. It is a single-board OEM GNSS-inertial solution that combines a survey-grade multi-frequency GNSS receiver with MEMS inertial sensors, and it supplies position and orientation for direct georeferencing of cameras, LiDAR and other mapping sensors on small unmanned aircraft.

Direct georeferencing means that the position and attitude of each image or LiDAR range are computed at the sensor itself, rather than being derived from many ground control points. With the module, the position is translated from the antenna to the camera perspective centre or LiDAR reference point using the measured orientation, and the exact time of each camera exposure is logged in GNSS time. This reduces the ground survey effort and the sidelap needed, so a mission covers more area per flight. The module also gives the autopilot a redundant navigation solution, and the real-time heading, once aligned, does not depend on a magnetometer.

The main figures are an output rate of 100 Hz for position, roll, pitch and heading, and an inertial data rate of 200 Hz. The receiver has 336 channels and tracks GPS, GLONASS, BeiDou, Galileo, QZSS, SBAS and L-band services such as Trimble RTX. Typical RMS position error is 1.5 to 3.0 m in standalone SPS mode, 0.02 to 0.05 m with RTK corrections, 0.03 to 0.06 m with post-processed CenterPoint RTX and 0.02 to 0.05 m with post-processing. Roll and pitch error is 0.04, 0.03, 0.025 and 0.025 degrees in the same four modes, and true heading error is 0.30, 0.18, 0.08 and 0.08 degrees. These are typical values that depend on satellite geometry and atmospheric conditions, and heading error rises at low speed and in hover.

For integration, the board is 67 x 60 x 15 mm and weighs 60 g. It accepts 9 to 30 V DC and draws a typical 3.5 W. The 44-pin header carries the I/O, and the antenna port is an MMCX receptacle that supplies 3.3 to 5 V at up to 400 mA to an active antenna with at least 28.5 dB of LNA gain. The interfaces are Ethernet with TCP/IP, UDP and a web interface, an RS232-level port, a 3.3 V TTL port, a PPS output, two event inputs for camera or sensor triggers, three digital I/O lines and a USB 2.0 device port for external logging, along with 6 GB of internal flash memory. Output formats are NMEA-0183 and Trimble GSOF, and accepted reference inputs include CMR, CMR+, sCMRx and RTCM 2.1, 2.2, 2.3, 3.0 and 3.1. Gimbal encoder and autopilot angles can be fed in for stabilised mounts.

Operating temperature is -40 to +75 °C, storage is -55 to +85 °C, survival shock is 75 g, and the sensors measure +/- 6 g and +/- 300 degrees per second. Applanix POSPac UAV post-processing software is part of the solution and supports Trimble CenterPoint RTX, which gives centimetre-level results without a base station.