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the Robot Construction Kit

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Base Types

Introduction

The package base/types contains a collection of C++ types that are shared between modules. The general policy is that if there is more than one library that generates a certain datatype, that type should go into the base/types library. In general, types in base should be compatible to oroGen, so that they can be used as interface types between tasks.

Further, there is a distinction between basic shared types and types that represent sensor samples. In general sensor information should always be timestamped. The convention is that types in samples always have a time member, which is of type base::Time. All types in base are in the base namespace. Samples are in the base::samples namespace.

Having shared types is very important to maintain interoperability between libraries. Whenever new types are generated, it should be considered if not one of the existing types in base can be used, or related types in other packages can be generalized and moved into base.

Basic Types

Following is a list of basic types and how they should be used. For more information please refer to the api docs of the base/types package.

Time

base::Time is one of the most used types. It internally represents the time as microseconds since UNIX epoch. It can be used to represent both absolute and relative time.

#include <base/time.h>

// initialize time to 0
base::Time t0 = base::Time();              
// get the current time
base::Time tnow = base::Time::now();
// get a time of 2.5 seconds 
base::Time t1 = base::Time::fromSeconds( 2.5 );
// tpast would be the time 2.5 seconds ago
base::Time tpast = tnow - t1;

Use toString() to get a human readable form. Also, there is a stream operator for the Time class.

TimeMark

Small convenience class to simplify benchmarking. It will record the time on generation, and has a simple stream method for the output.

#include <base/timemark.h>
#include <iostream>

base::TimeMark mark("Complex Stuff");
// do complex stuff
...
std::cout << mark << std::endl;

Angle

The base::Angle class represents an angle and can be used as a convenience class instead of a float. An angle object has a canonical interpretation within -M_PI and M_PI. It can also perform converting between radians and degrees.

#include <base/angle.h>

// storing angles and the canonical form
base::Angle a = base::Angle::fromDegree(540.0);
base::Angle b = base::Angle::fromRad(M_PI);
a.isApprox( b ); // is true

// converting from degree to rad 
needsRad( base::Angle::deg2Rad( 180.0 ) );

Matrix / Vector

The base types use the Eigen3 library for handling and representing matrices and vectors. Eigen types have special constraints regarding alignment, which require special template parameters to be used for using Eigen types as interface types. To simplify this, base declares a number of typedefs, which are equivalent to the corresponding Eigen types, but having alignment switched off.

  • base::Vector2d
  • base::Vector3d
  • base::Matrix2d
  • base::Matrix3d
  • base::Matrix4d
  • base::Quaterniond
  • base::Affine3d

Also have a look at the wiki page on the subject. Also, for the eigen types, the opaque mechanism is used.

Pose

For the base types, the base::Pose type is considered a type, which has a 3d orientation and position member. The pose is used to represent the position and orientation of the robot. There is also base::Pose2D, which is the equivalent for the 2D case. Note, that both base::Pose and base::Affine3d represent the same type of data. The Affine3d class is more verbose, but also more effective to compute with. In general, the base::Pose should be used for interfacing, while Affine3d is likely to be used in places where a lot of transformations are involved.

Motion Command

Is a collection of different types, that are used for interfacing generic control commands. The types are mostly generic to certain domains (e.g. underwater, UGV a.s.o).

Odometry

The base/odometry.h header contains interface classes, which can be implemented by odometry models. There is a distinction between 2d and 3d, as well as Gaussian and sampling models.

Waypoint

Contains a class which represents a waypoint, which consists of a point, a heading as well associated uncertainties.

Samples

As mentioned above, samples are types time tagged types, which all contain a time field of type base::Time. Samples are usually used to represent sensor or state information. The following files are in the samples directory of the base package.

  • frame - is the basic class to represent image frames.
  • imu - contains imu sensor readings, which is a combination of accelerometer, magnetometer and gyros
  • laser_scan - sample from a laser range finder (line)
  • pointcloud - basic datatype for representing point cloud information
  • rigid_body_state - is used to represent position and velocity information between to reference frames including uncertainty.
  • sonar_scan - sample from a sonar range image (underwater)

Actuators

TODO