# Distance measure in gazebo?

**Could anyone tell me 1 coordinate unit = ? meter?**
My heightmap image's size is 65*65. If i set in sdf file: heightmap's size is (x,y,z) = 65 * 65 * 2, then i see my terrain x coordinate will range from -32 to + 32.

If i set in sdf file: heightmap's size is (x,y,z) = 131 * 131 * 2, then i see my terrain x coordinate will range from -65 to + 65.

**But in the above two cases, the following relationship between delta_X and traveled distance still hold:**
Traveled distance = 5 * delta-X
(My car runs along x axis and i use the following function time by time to get delta-X within time of delta-t:

math::Pose orig_pose = this->model->GetWorldPose().pos.x ) So does this make sense? and are there any other better method to measure traveled distance?

Thanks