motion

type Orientation struct {
	Pitch float64 `json:"pitch"` // the top raised toward you; 90 is upright
	Roll  float64 `json:"roll"`  // the right edge dipped down; 90 is on its side
	// Yaw is the turn around the screen's axis. On Android it's from
	// north; on iOS it's from wherever it began, so only changes in it mean
	// anything there.
	Yaw float64 `json:"yaw"`
}

type Reading struct {
	Accel Vector `json:"accel"` // the accelerometer, in g, gravity included
	Gyro  Vector `json:"gyro"`  // the gyroscope, in radians a second
}

type Vector struct {
	X float64 `json:"x"` // across the screen, positive to the right
	Y float64 `json:"y"` // up the screen, positive to the top
	Z float64 `json:"z"` // out of the screen, positive toward you
}