Added calibrate command to UdpControl and Client

[wiseman]

Added a new AT command, "CALIB", which according to the SDK docs "asks the drone to calibrate the magnetometer (must be flying)."

Tested from a repl. Note that this causes the drone to yaw 360 degrees.

The command takes a single argument, which is a device number. Currently the only device the SDK defines is the magnetometer, which is device number 0.

[yocontra]

What was your use case for adding this? Just curious

[wiseman]

I want to be able to get accurate magnetometer/compass/heading info for things like augmented reality overlays and display on the ardrone-webflight HUD.

[wiseman]

Note that to enable magnetometer values in navdata, you need to do

function navdata_option_mask(c) {
  return 1 << c;
}

// From the SDK.
var default_navdata_options = (
  navdata_option_mask(arDroneConstants.options.DEMO) |
  navdata_option_mask(arDroneConstants.options.VISION_DETECT));

client.config('general:navdata_options',
              default_navdata_options |
              navdata_option_mask(arDroneConstants.options.MAGNETO));

This implies it might be useful to add a navdata_option_mask function and export the constants from node-ar-drone.

[yocontra]

LGTM - just needs some documentation on the README

[yocontra]

Also I agree we should be exporting the constants (and as much as possible) from the module. Looking forward to a PR for that

[felixge]

@wiseman :sparkling_heart: thx for the patch!