Install a Tuffwing Hot Shoe Precision Geotag Cable
 

$39.95

Overview

You can improve the accuracy of your geotags and you are less likely to encounter mismatches between your Pixhawk log file and number of images taken if you install a hot shoe precision geotag cable. The cable slides into a hot shoe and senses when your camera takes a picture. The hot shoe activates exactly and only when the shutter opens. This corrects shutter lag and accounts for missed or extra photos. Do the following to install and configure your Tuffwing hot shoe precise geotag cable and Pixhawk autopilot.

The hot shoe cable works with any camera with a hot shoe.

Requirements

Slide the cable into your hot shoe

  1. Gently slide the cable into your hot shoe. Do not force. The spring loaded contact pin is fragile. If it snags, then place a strip of paper under it while sliding it in to the hot shoe.
  2. Apply a small amount of [non-permanent] hot glue to the edge of the hot shoe cable. Disconnect at the servo cable.

Configure your Pixhawk

  1. Plug the precision geotag cable into an open AUX port on your Pixhawk (Pin 50-55).
  2. Use Mission Planner to connect to your Pixhawk based UAV. Go to CONFIG/TUNING > Full Parameter Tree and set the following.

    3. CAM_FEEDBACK_POL 0

    CAM_FEEDBACK_PIN 53.

  3. Fly a mission and take pictures.
  4. Geotagging instructions.

 Understanding CAM and TRIG events in your Pixhawk log file

Each time you camera takes a picture your Pixhawk records a CAM event in the log file. It looks like this:

CAM 321916644 515572200 1893 29.88722 -98.8196 573.64 100.22 564.3 -28.47 7.85 74.09

If CAM_FEEDBACK_PIN is set to -1, then each time the Pixhawk triggers the camera a CAM event is recorded. However, if CAM_FEEDBACK_PIN is set to to 50-55, then a TRIG event will be recorded each time the Pixhawk triggers the camera and a CAM event will be recorded each time a feedback signal is received by the Pixhawk. Geotagging programs still work the same way - with CAM events in the log file. The TRIG events are useful for troubleshooting. Do the following to verify you're properly logging CAM and TRIG events:

  1. Open your log file with Excel. Choose comma delimited.
  2. Sort the data by Column A.
  3. Find all CAM events, copy them, then paste into a new worksheet.
  4. Find all TRIG events. copy them, then past into the same new worksheet.
  5. Sort the data by Column C. This is GPS time in milliseconds.
  A B GPS Time in Milliseconds
  TRIG 314478180 515564800 1893 29.88832 -98.8201 576.27 102.85 566.79 0.99 2.36 175.88
  TRIG 315478238 515565800 1893 29.88813 -98.8201 575.28 101.86 565.99 -4.01 2.59 175.05
  CAM 321916644 515572200 1893 29.88722 -98.8196 573.64 100.22 564.3 -28.47 7.85 74.09
  CAM 327315518 515577600 1893 29.88764 -98.8191 573.74 100.32 564.93 -7.06 5.13 358.09
  TRIG 332078554 515582400 1893 29.88809 -98.8192 573.51 100.09 565.9 5.11 4.19 359.23
  CAM 333097187 515583400 1893 29.88818 -98.8192 572.66 99.24 565.1 4.52 4.98 2.1
  TRIG 334078609 515584400 1893 29.88828 -98.8192 572.77 99.35 565.03 1.52 8.7 6.26
  CAM 334356899 515584600 1893 29.8883 -98.8192 572.92 99.5 565.13 4.52 10.2 5.79
  TRIG 336078350 515586400 1893 29.88846 -98.8192 574.23 100.81 566.35 -2.11 7.49 4.72
  CAM 336356375 515586600 1893 29.88848 -98.8192 574.33 100.91 566.48 -2.24 9.02 4.61
  TRIG 338078436 515588400 1893 29.88863 -98.8191 574.54 101.12 566.96 -1.37 5.25 0.37
  CAM 338356182 515588600 1893 29.88865 -98.8191 574.49 101.07 567.02 -1.38 5.65 1.82
  TRIG 340078440 515590400 1893 29.88881 -98.8191 573.23 99.81 566.32 -6.36 5.69 2.36
  • In the data above, the camera was triggered twice before a picture was taken, then two pictures before the next TRIG. This is caused by the lag of the first picture.
  • Clean TRIG followed by CAM after the initial lag.
  • Use Excel to count the number of CAM messages to compare to the number of photos taken.
  • Geotag your images and enjoy the tightest blue and green dots you've ever seen.

Errata, kudos, brian.christal@gmail.com