Event logger

Features

• ~1 micro second precision
• Up to 4 source channels:
  • IMU
  • GPS
  • Image Acquisition
  • External General Purpose Input (e.g., odometer - 3..5V pulses)

Description

The FPGA-based Event Logger uses local clock for time-stamping, so each log entry (IMU, GPS, Image Acquisition and External Input) is recorded with timing info.

In a single camera each acquired image has a timestamp in its header (Exif). The log entry for images has this timestamp recorded at the logger (local) time.

Multiple cameras (e.g., Eyesis4π) are synchronized by the master camera to sub-microsecond, and each acquired also image has the master timestamp in Exif. The log entries for images (if logged in the camera other than master so with different local clock) have 2 fields - master timestamp (same as in image Exif) and local timestamp (same clock as used for IMU), so it is easy to match images with inertial data.

A typical log record has the following format:

[LocalTimeStamp] [SensorData]
Examples or parsed records:
[LocalTimeStamp]: IMU: [wX] [wY] [wZ]  [dAngleX] [dAngleY] [dAngleZ] [accelX] [accelY] [accelZ] [veloX] [veloY] [veloZ] [temperature]
[LocalTimeStamp]: GPS: [NMEA sentence]
[LocalTimeStamp]: SRC: [MasterTimeStamp]

Syncing with an external device

An external device (e.g., odometer) can be connected with a camera / camera rig.

The device have to send HTTP requests to be logged to the camera on http://192.168.0.221/imu_setup.php?msg=message_to_log (message is limited to 56 bytes) and 3..5V pulses on the two middle wires of the J15 connector. !! Make sure only the two middle wires are connected and the externals one are not. Since the camera's input trigger is optoisolated, but not the trigger output. !!

For testing purposes we used an Arduino Yún with Adafruit Ultimate GPS Logger Shield. The GPS was used only to send a PPS to the camera's J15 port while Arduino Yún was running a simple script such as:

echo "" > wifi.log ; i=0; while true; do wget http://192.168.0.221/imu_setup.php?msg=$i -O /dev/null -o /dev/null; echo $i ; echo $i >> wifi.log ; iwlist wlan0 scan >> wifi.log ; i=`expr $i + 1`; done

This script is logging an incrementing number both to the camera log and Yún's file system, WiFi scanning is also recorded to the Yún's log. So later both log files can be synchronized in post-processing.

How to record log on the camera

(see http://192.168.0.9/logger_launcher.php source for options and details):

• START: http://192.168.0.9/logger_launcher.php?file=/absolute_path/name.log&index=1&n=10000000&mount_point=/absolute_path

mount_point=/absolute_path/ - the path at which the storage is mounted (usb or nfs)

• STOP: http://192.168.0.9/phpshell.php?command=killall%20-1%20log_imu

Notes

• GPS data is written to both, the event log and the image header (Exif).
• IMU data is written only to the event log.
• Example IMU (ADIS16375) samples rate is 2460Hz.
• Example GPS receiver (Garmin 18x serial) samples rate is 5Hz in NMEA or other configured format.

Examples

Raw

Raw *.log files are found here

Parsed

parsed_log_example.txt (41.3MB) - here

Tools for parsing logs

Download one of the raw logs.

• PHP: Download read_imu_log.php_txt, rename it to *.php and run on a PC with PHP installed.
• Java: Download IMUDataProcessing project for Eclipse.