UpdateOdometryEncoder generating wrong twist data in odometry when in encoder mode for gazebo_ros_diff_drive.cpp

[altineller]

Hello,

This is both a problem and fix at the same time. :)

In void GazeboRosDiffDrivePrivate::UpdateOdometryEncoder(const gazebo::common::Time & _current_time)

double v = sqrt((dx * dx) + (dy * dy)) / seconds_since_last_update;

This will always generate a positivie number,, which is used for odom_.twist.twist.linear.x = v;

I was simulating the EKF filter with gazebo when I noticed it did not work in reverse. It generates corrects results for pose, so it is not visible unless you plugin an ekf node, which uses the twist from odom.

I have not generated a fix yet, but it will be easy.

Any ideas, or recomendations greatly appreciated.