Class ChassisDisplacementObserverInterface

Class Documentation

class ChassisDisplacementObserverInterface

Interface for getting chassis displacement in chassis frame

Implementations of getChassisDisplacement should return the absolute chassis displacement in the chassis frame since some arbitrary time at startup. Note this value does not have a useful physical interpretation (e.g.: a robot that drives a complete circle going forward and returns to it’s original point will have a positive absolute x-displacement in chassis frame corresponding to the circle’s circumference).

This absolute value return was chosen over a volatile getter that returned displacement since last call to avoid having getter modify the state of the class (and thus avoid concerns about multiple consumers sharing this object)

To generate useful measurements in a non-rotating reference frame from this getter users should differentiate this returned value by sampling this value frequently, finding the delta position, and orienting that displacement so that it matches the reference frame, then adding that displacement to the tracked chassis position.

While on flat ground, the chassis positive z-axis is defined as “up” (opposite gravity), positive x-axis is defined as the chassis forward vector, and thus consequently the positive y-axis is chassis “left”.

Getting chassis displacement may fail as implementor chooses to indicate either values are too stale or sensor went offline etc.

Most implementations probably will not support getting z-displacement, and in that case should just return 0 for z-displacement.

Note

The RoboMaster robot building specification manual mentions a coordinate convention for chassis orientations. Their coordinate convention is different in that they assert positive z as pointing “towards the center of the Earth”.

Public Functions

virtual bool getVelocityChassisDisplacement(modm::Vector3f *const velocity, modm::Vector3f *const displacement) const = 0

Returns the chassis displacement in chassis frame since some fixed arbitrary point in time near startup.

Parameters:

  • velocity – [out] if valid data is available the x, y, and z of this pointed to vector that will be populated with the appropriate velocity in implementation specific units.

  • displacement – [out] if valid data is available the x, y, and z of this pointed to vector will be populated with the appropriate absolute displacement in implementation specific units.

Returns:

true if valid chassis displacement data was available, false otherwise.