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rotationeigenangle

Getting rotation angle from Eigen::Isometry2d

I'm working with Eigen library and, in particular, 2d isometries to represent the pose of an object in a 2D world.

As you may know, this has three components: x and y for the position and an angle theta for the rotation.

Extracting the position components is straightforward:

Eigen::Isometry2d t;
double x = t.translation().x();
double y = t.translation().y();

For the rotation, one can use a formula like:

double theta = atan2(t(1, 0), t(0, 0));

This is tested and works fine, but it's a bit inconvenient to write it all the times. Therefore my question is if someone knows a nicer way to get theta by just calling Eigen methods.

Solution

  • You can construct a Rotation2Dd object from the linear part of the transformation (and if you prefer having a scalar, extract the angle using .angle()):

    double theta = Eigen::Rotation2Dd(t.linear()).angle();