Strict type checks (#197) on python interface of Buffer::setTransform make direct input from bagfile cumbersome

[stwirth]

#197 introduced new type checks on the python interface of Buffer::setTransform to fix #159.
Unfortunately this makes filling a tf buffer from a bagfile cumbersome, as bagfiles have their own type definitions for messages.
Here is an example program that demonstrates the problem:

import tf2_ros
import rosbag
from geometry_msgs.msg import TransformStamped, Vector3, Quaternion

def set_transform_test(t):
    print "setting transform of type {}".format(type(t))
    tf2_buf = tf2_ros.Buffer(None, False)
    tf2_buf.set_transform(t, 'default_authority')

if __name__ == '__main__':
    # create dummy transform
    t = TransformStamped()
    t.header.frame_id = 'parent'
    t.child_frame_id = 'child'
    t.transform.translation = Vector3()
    t.transform.rotation = Quaternion(0, 0, 0, 1)

    set_transform_test(t)

    # write transform to bag and read it again
    wbag = rosbag.Bag('test.bag', 'w')
    wbag.write('transform', t)
    wbag.close()

    rbag = rosbag.Bag('test.bag', 'r')
    for topic, msg, t in rbag.read_messages(topics=['transform']):
        set_transform_test(msg)
    rbag.close()

This is the output:

$ python tf_bag_test.py 
setting transform of type <class 'geometry_msgs.msg._TransformStamped.TransformStamped'>
setting transform of type <class 'tmpTmLCns._geometry_msgs__TransformStamped'>
Traceback (most recent call last):
  File "tf_bag_test.py", line 28, in <module>
    set_transform_test(msg)
  File "tf_bag_test.py", line 9, in set_transform_test
    tf2_buf.set_transform(t, 'default_authority')
TypeError: transform.translation must be of type Vector3

To work around this you need to manually transform the type tmpTmLCns._geometry_msgs__TransformStamped to type geometry_msgs.msg._TransformStamped.TransformStamped.

I would propose to make the type checks less strict, e.g. just enforcing that the transform has a member translation which has three floating point values and a member rotation that has four.

/cc @spaghetti-

[spaghetti-]

Good catch, I think that enforcing members translation and rotation is good enough as well. I'll try to send in a PR this week.

[stwirth]

awesome!

[spaghetti-]

Gave some thought to it, it would seem like we have to ensure that the members translation and rotation have their own sufficient members as well.

[spaghetti-]

After the above patch is applied, with your test program we have:

test.py:8: UserWarning: translation should be of type Vector3
  tf2_buf.set_transform(t, 'default_authority')
test.py:8: UserWarning: translation should be of type Quaternion
  tf2_buf.set_transform(t, 'default_authority')
setting transform of type <class 'geometry_msgs.msg._TransformStamped.TransformStamped'>
setting transform of type <class 'tmpApvwFZ._geometry_msgs__TransformStamped'>

[pklip]

Hi, I also ran into this (not so obvious) problem. It is also hard to work with the Python bindings, because the tf_ros2 documentation (for Python) in virtually nonexistent: http://docs.ros.org/kinetic/api/tf2_ros/html/python/tf2_ros.html
Could someone please point me to where to add documentation as a pull request?

[tfoote]

@ros-pull-request-builder test this please

[tfoote]

@pklip A PR for filling out the documentation would be greatly appreciated. It's source is here: https://github.com/ros/geometry2/tree/indigo-devel/tf2_ros/doc

[tfoote]

Fixed in #221