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Module vector3d

Vector3d Class

This represents a vector in a 3D space which can be a magnetic field, an acceleration or a rotation rate. It has read-only x y and z properties which represent the vector's components relative to the vehicle containing the sensor. It supports cases where the sensor is mounted orthogonally to the vehicle coordinates: sensor fusion assumes that the x axis corresponds to the front of the vehicle, y is left-right, and z is vertical.

The class's internal storage uses Cartesian coordinates relative to the sensor.

Methods

Users of the IMU classes need not be concerned with the constructor as this is used only by the IMU classes.

Vector3d() Constructor has three mandatory arguments

  1. transposition a 3-tuple which must contain three unique integer values from 0 to 2. It relates vehicle axes to sensor axes. Hence (0,1,2) effects no change. (1,0,2) interchanges the x and y axes for the case where the sensor is rotated through 90 degrees in the horizontal plane.
  2. scaling A 3-tuple with each element normally being 1 or -1. Returned x, y and z values are multiplied by the corresponding value in the tuple. Allows axes to be inverted.
  3. update_function Normally a method of the class of which the Vector3d() is a member. It is called when the user accesses Vector3d() properties which require the sensor to be read. It will update the Vector3d() internal _vector[] and _ivector[] lists.

calibrate() Optional method to enable fixed offsets to be stored and allowed for. Arguments:

  1. Stop function: routine will run until this passed function returns False.
  2. Wait function: Optional. Default is a 50mS delay between readings. User can supply an alternative, for example a thread-aware delay in cooperative multitasking environments.

The function takes repeated readings until stopped, when it stores the average vector as a 3-tuple in the cal property. This is then used in subsequent x, y, z and xyz readings. Note that the calibration procedure for the magnetometer involves rotating the sensor around each orthogonal axis. For the gyro the unit should be held stationary. Calibration is not normally required for accelerometer but I would expect it to be performed with device rotation as per the magnetometer.

Properties

x y z float read only
These return the scaled vehicle relative coordinates.

xyz float 3-tuple read only
Returns a 3-tuple (x,y,z) of scaled vehicle relative coordinates. Note that the above properties cause the device x, y and z values to be read. Use xyz if timing is critical or if it is necessary that all three values should originate at the same instant.

ix iy iz integer read only
Return unscaled, sensor relative, integer coordinates as read from the device.

ixyz integer 3-tuple read only
Returns (x,y,z) of sensor relative, integer coordinates as read from the device. The integer reads do not provoke a device read, returning the last data to be read by any method.

transpose integer 3-tuple read only
Returns transposition 3-tuple as passed to constructor.

scale integer 3-tuple read only
Returns scaling 3-tuple as passed to constructor.

magnitude float read only
Returns the absolute magnitude of the vector.

azimuth float read only
Returns the angle (in degrees) between y and x vector components.

elevation float read only
Returns the angle (in degrees) of the vector relative to the xy plane such that a horizontal vector will return zero degrees.

inclination float read only
Returns the angle (in degrees) of the vector relative to the xy plane such that a horizontal vector will return 90 degrees. This is typically used with the accelerometer where a horizontal sensor or vehicle will have vector components of approximately (0.0, 0.0, 1.0) and an inclination of zero.

cal float 3-tuple
Holds the calibration offsets.