subscribing to /tf returns only a partial list
I am trying to get all of the tf frames and am subscribing to /tf I am using TFMessage which I expect to return an array of TransformStamped messages. It does do that, but the list is incomplete-- it seems to only return one section of transforms. Using rostopic echo /tf I see several transforms sections:
transforms: -
several TransformStamped messages will appear here
transforms: -
several different TransformStamped messages appear here
But when I try to subscribe in code, only one of those transforms sections show up:
from tf2_msgs.msg import TFMessage
msg = rospy.wait_for_message("/tf", TFMessage)
print("number of transforms in tf = ", len(msg.transforms))
for entry in msg.transforms:
print(entry)
I just get a single section of transforms seen from rostopic echo /tf
What am I doing wrong?
Some insight-- there are 4 different nodes publishing to tf, so any single tf message will only have the transforms from the node that published it. Now the question becomes how to know when you have received messages from all the nodes, so that you know you have received all the available transforms.
I believe this is by-design. Every broadcaster only 'knows' about its own transforms. Subscribing directly to the topic itself is not often done, as it's the job of
Buffers andTransformListeners to consume those messages and build up the tree structure for clients.as TF is an implementation of an asynchronously distributed tree structure, you can't know this. How would you define "all transforms" anyway, seeing as there is a time-dimension to it: node A could publish transform X at any point in time. Especially with dynamic applications this is not a strange thing to happen.
Could you perhaps tell us what you are trying to achieve? Your question reads as-if you're trying to do this to solve ...(more)