# Rtab map stereo visual odometry pose scale?

Hello I'm kind of new to ROS, I'm trying to use the stereo visual odometry of RTAB map to produce odometry for localization, I have tried it on gazebo, the pose in the odom topic is translated in gazebo as one grid cell, what i don't understand is what is the ground truth for the pose when using real stereo camera? is it 1 meter for every change in X or Y? and how can i specify the unit of the pose?

Originally posted by 3bkr on ROS Answers with karma: 3 on 2020-04-16

Post score: 0

It will be the units used during the calibration of the stereo camera (checkboard size). In general, the units will be in meters.

Originally posted by matlabbe with karma: 6409 on 2020-04-17

This answer was ACCEPTED on the original site

Post score: 1

Comment by 3bkr on 2020-04-18:
Thank youu

Comment by 3bkr on 2020-04-19:
Hello again, I have tried using a stereo camera and i have a problem, the scale is not logical on high speed, i have tried moving in a straight line in the X direction for 100 meters on a speed 40 km/h and it gives not logical numbers, is that normal or I have a problem? Thanks in advance

Comment by matlabbe on 2020-04-21:
It could be a tracking problem, but units should always be the same. What kind of camera do you use? If the cameras are not synchronized, it may affect the scale when moving.

Comment by 3bkr on 2020-05-05:
Hello thanks alot for your reply What do you mean by tracking problem? I’m using two synchronized leopard imaging cameras for stereo and for the calibration i used the camera calibration package

Comment by matlabbe on 2020-05-12:
If visual odometry fails to or wrongly match features, it could create wrong transformations. Maybe I didn't understand what you mean by "it gives not logical numbers".

Comment by 3bkr on 2020-05-12:
Sorry i meant the result is not logical, for example i drive for 100 meters in a straight line so the X in pose is supposed to be 100 in the odom topic but the result is 2

Comment by matlabbe on 2020-05-13:
do you have a database to share?