Install a Tuffwing Canon 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 precision geotag cable. The cable contains a phototransistor that picks up a red eye reduction LED flash when your camera takes a picture. The LED flashes exactly and only when the shutter opens. This corrects shutter lag, missed photos, or extra photos. Do the following to install and configure your Tuffwing precise geotag cable, CHDK enabled Canon point and shoot camera, and Pixhawk autopilot.

Requirements

Verify your camera will flash its red eye reduction LED

Not all Canon point and shoots will work. Do the following to verify your red eye reduction LED can be properly flashed.

  1. Install KAP UAV Exposure Control Script 3.8 on your Canon point and shoot camera.
  2. Load KAP_UAV_3-8.lua Set Shot Interval to Burst.
  3. Set USB Shot Control to None. Set it back to Pixhawk after you verify your red eye reduction LED is properly flashing.  
  4. Set Shot Sync LED to 0. Note, this works for Canon S110s. You may need to choose a different number for your camera.
  5. Press the MENU button to exit the script editor, then 1/2 press the Shutter button to start the script.
  6. Your red eye reduction LED should flash like the video. If it doesn't, then change Shot Sync LED to 1, then 2, etc. If your red eye reduction LED won't flash like the video, then your camera will not work with the cable.

Attach the cable to your camera

  1. There is a thin layer of non-permanent black hot glue on the back of the cable. Carefully warm the glue and camera with a heat gun.
  2. Align the phototransistor over the red eye LED and attach the cable as shown.

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 55. Do not use Pin 54.

  4. Fly a mission and take pictures.
  5. Geotag images using Mission Planner. Control F, use CAM Messages.

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 (disabled), then each time the Pixhawk triggers the camera a CAM event is recorded. However, if CAM_FEEDBACK_PIN is set to to 50-55(enabled), 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 lat long alt
  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