README

tf2_2d

A set of 2D geometry classes modeled after the 3D geometry classes in tf2.

Using tf2 toMsg() and fromMsg()

I’ve tried to include fromMsg() implementations for anything that remotely makes sense. The tf2 toMsg() signature does limit its use to a single output type, so I’ve had to make a guess as to the most useful variation there.

For example:

#include <tf2_2d/tf2_2d.h>     // This header includes the tf2 conversion functions
#include <tf2_2d/transform.h>  // Then include what you use

// Convert a tf2_2d object into a 3D message
auto transform_2d = tf2_2d::Transform(1.0, 1.5, 2.0);
geometry_msgs::Transform transform_3d_msg = tf2::toMsg(transform_2d);

// Convert a 3D message into a 2D tf2_2d object
geometry_msgs::Transform transform_3d_msg;
tf2_2d::Transform transform_2d;
tf2::fromMsg(transform_3d_msg, transform_2d);

// You can do Stamped<> things as well
auto transform_2d = tf2::Stamped<tf2_2d::Transform>(tf2_2d::Transform(1.0, 1.5, 2.0), ros::Time(1.2), "frame");
geometry_msgs::TransformStamped transform_3d_msg = tf2::toMsg(transform_2d);

Conversion of Points and Quaternions are also supported, as are conversions to other datatypes that are handled by tf2’s conversion system.

Transformation math

The tf2_2d types also implement all of the expected transformation math.

auto v1 = tf2_2d::Vector2(1.0, 2.0);
auto v2 = tf2_2d::Vector2(1.5, 2.5);
auto v3 = v1 + v2;                             // v3 == (2.5, 4.5)

tf2_2d::Rotation r1(M_PI);
auto v4 = r1.rotate(v1);                       // v4 == (-2.0, 1.0)

auto t1 = tf2_2d::Transform(1.0, 2.0, 3.0);
auto t2 = tf2_2d::Transform(-2.0, -1.0, -1.5);
auto t3 = t1 * t2;                             // t3 == (3.12, 2.70, 1.5)

auto t4 = tf2_2d::Transform(1.0, 2.0, 3.0);
auto t5 = tf2_2d::Transform(-2.0, -1.0, -1.5);
auto t6 = t4.inverseTimes(t5);                 // t6 == (2.54, 3.39, 1.78)

The tf2_2d::Rotation class deserves a few additional notes. The angle stored in a Rotation object is always within the (-Pi, Pi] range. You can construct a Rotation object with any floating point value, but it will be wrapped to that range. You can also perform arithmetic with the angles, without worrying about wrapping issues.

tf2_2d::Rotation r1(1.0);
auto r2 = 17.0 * r1;       // r2.angle() == -1.84956

tf2_2d::Rotation r3(1.0);
tf2_2d::Rotation r4(3.0);
auto r5 = r3 + r4;         // r5.angle() == -2.28319

tf2_2d::Rotation r6(-3.0);
tf2_2d::Rotation r7(1.0);
auto r8 = r6 - r7;         // r8.angle() == 2.28319

Additionally, the tf2_td::Rotation class caches the sin/cos results needed to perform rotations. So, once a Rotation object is used to rotate something, the trig functions will never be evaluated again. And the cached sin/cos values will propagate to any derived objects that it can. This includes the Rotation object built into a Transform.

tf2_2d::Vector2 v1(1.0, 2.0);
tf2_2d::Rotation r1(1.0);            // No sin/cos calls have been made, since it is not needed yet
auto v2 = r1.rotate(v1);             // Computes sin/cos and remembers it
auto v3 = r1.unrotate(v2);           // Does not need to compute sin/cos again
tf2_2d::Rotation r2 = r1;            // Transfers sin/cos to r2
auto v4 = r2.rotate(v1);             // Does not need to compute sin/cos because it stole the cached values from r1
tf2_2d::Rotation r3 = r1.inverse();  // Inverts and transfers sin/cos to r3
auto v5 = r3.rotate(v1);             // Does not need to compute sin/cos because it stole the cached values from r1