Can you update pose of either frame after setting static transform?
I have set up a simple tree: odom->base_link->odom_sensor.
The odom sensor is offset from the centre of the robot and output's Odometry messages in the odom reference frame. I need to transform these messages essentially so they describe the transform between odom and base_link.
I have set a static transform from base_link to odom_sensor and that works well to transform the Odometry Twist messages.
My plan was to use set the transform between the odom and odom_sensor using the Pose from the odometry sensor, then lookup the transform from odom to base_link. (I might have to invert it as lookup_transform returns transform that will transform a pose not a frame).
If I update the TF tree to change odom to base_link I see that the pose of odom_sensor updates as it should. But if I update odom to odom_sensor I find that the pose of base_link doesn't update. Can I not update the pose of the child in the static transform?
I could set a static transform from odom_sensor->base_link, such that the tree was odom->odom_sensor->base_link. But that is a pain, as I have other inputs that can update odom->base_link.
I feel like my best option is to work out how to apply the offset odom_sensor->odom->base_link myself, and then update the tree with odom->base_link afterwards (using the static transform base_link -> odom_sensor to update the pose of odom_sensor).
Keep in mind that your tf tree must be a tree. Meaning any given frame can have only one parent. Based on the text in your question, it sounds like you might be changing the parent of
odom_sensorsuch that it is sometimesbase_linkand other timesodom. You cannot do this, and if you do all bets are off regarding any future calculations that will require tree parsing. Once you've defined a tree structure, if you need to update transforms the updates should maintain the structure. http://wiki.ros.org/tf/FAQ#Frames_are...Yes, thank you for confirming. You are essentially right - Odometry from the sensor and for the robot have the world frame (
odom) as a parent. I need to compute the Odometry for the robot (in theodomframe) from the sensor Odometry (also in theodomframe), but given the tree isodom->base_link->odom_sensorI can't directly update the pose of theodom_sensorframe in theodom(grandparent) then look upodomtobase_linkas I hoped.After much head scratching (and many unit tests) I have now worked out how to do the transformation to account for the offset between the sensor and robot centre. I compute this then update
odom->base_link, then (if I need it) the pose of theodom_sensorinodomupdates too.