tf2

exception tf2.TransformException

base class for tf exceptions. Because tf2.TransformException is the base class for other exceptions, you can catch all tf exceptions by writing:

try:
    # do some tf2 work
except tf2.TransformException:
    print "some tf2 exception happened"

exception tf2.ConnectivityException

subclass of TransformException. Raised when that the fixed_frame tree is not connected between the frames requested.

exception tf2.LookupException

subclass of TransformException. Raised when a tf method has attempted to access a frame, but the frame is not in the graph. The most common reason for this is that the frame is not being published, or a parent frame was not set correctly causing the tree to be broken.

exception tf2.ExtrapolationException

subclass of TransformException Raised when a tf method would have required extrapolation beyond current limits.

exception tf2.InvalidArgumentException

subclass of TransformException. Raised when the arguments to the method are called improperly formed. An example of why this might be raised is if an argument is nan.

BufferCore

class tf2.BufferCore(cache_time = rospy.Duration(10))

Parameter:cache_time – how long the buffer should retain transformation information in the past.

The BufferCore object is the core of tf2. It maintains a time-varying graph of transforms, and permits asynchronous graph modification and queries:

>>> import rospy
>>> import tf2
>>> import geometry_msgs.msg
>>> t = tf2.BufferCore(rospy.Duration(10.0))
>>> t.getFrameStrings()
[]
>>> m = geometry_msgs.msg.TransformStamped()
>>> m.header.frame_id = 'THISFRAME'
>>> m.child_frame_id = 'CHILD'
>>> m.transform.translation.x = 2.71828183
>>> m.transform.rotation.w = 1.0
>>> t.setTransform(m)
>>> t.getFrameStrings()
['/CHILD', '/THISFRAME']
>>> t.lookupTransform('THISFRAME', 'CHILD', rospy.Time(0))
((2.71828183, 0.0, 0.0), (0.0, 0.0, 0.0, 1.0))
>>> t.lookupTransform('CHILD', 'THISFRAME', rospy.Time(0))
((-2.71828183, 0.0, 0.0), (0.0, 0.0, 0.0, 1.0))

The transformer refers to frames using strings, and represents transformations using translation (x, y, z) and quaternions (x, y, z, w) expressed as Python a tuple. Transformer also does not mandate any particular linear algebra library. Transformer does not handle ROS messages directly; the only ROS type it uses is rospy.Time().

To use tf with ROS messages, see TransformerROS and TransformListener.

allFramesAsYAML() → string

Returns a string representing all frames, intended for debugging tools.

allFramesAsString() → string

Returns a human-readable string representing all frames

setTransform(transform, authority = "")

Parameters:

• transform – transform object, see below
• authority – string giving authority for this transformation.

Adds a new transform to the Transformer graph. transform is an object with the following structure:

header
    stamp             time stamp, rospy.Time
    frame_id          string, parent frame
child_frame_id        string, child frame
transform
    translation
        x             float
        y             float
        z             float
    rotation
        x             float
        y             float
        z             float
        w             float

These members exactly match those of a ROS TransformStamped message.

canTransform(target_frame, source_frame, time) → bool

Parameters:

• target_frame – transformation target frame in tf, string
• source_frame – transformation source frame in tf, string
• time – time of the transformation, use rospy.Time() to indicate present time.

Returns True if the Transformer can determine the transform from source_frame to target_frame at time.

canTransformFull(target_frame, target_time, source_frame, source_time, fixed_frame) → bool

Extended version of canTransform().

Parameters:

• target_time – The time at which to transform into the target_frame.
• source_time – The time at which to transform from the source frame.
• fixed_frame – The frame in which to jump from source_time to target_time.

clear() → None

Clear all transformations from the buffer.

lookupTransform(target_frame, source_frame, time) → geometry_msgs.msg.TransformStamped

Parameters:

• target_frame – transformation target frame in tf, string
• source_frame – transformation source frame in tf, string
• time – time of the transformation, use rospy.Time() to indicate most recent common time.

Returns:

position as a translation (x, y, z) and orientation as a quaternion (x, y, z, w)

Raises:

tf2.ConnectivityException, tf2.LookupException, or tf2.ExtrapolationException, or tf2.InvalidArgumentException

Returns the transform from source_frame to target_frame at time. Raises one of the exceptions if the transformation is not possible.

Note that a time of zero means latest common time, so:

t.lookupTransform("a", "b", rospy.Time())

will return the transform from “a” to “b” at the latest time available in all transforms between “a” and “b”.

lookupTransformFull(target_frame, target_time, source_frame, source_time, fixed_frame) → geometry_msgs.msg.TransformStamped

Parameters:

• target_frame – transformation target frame in tf, string
• target_time – time of transformation in target_frame, a rospy.Time
• source_frame – transformation source frame in tf, string
• source_time – time of transformation in target_frame, a rospy.Time
• fixed_frame – reference frame common to both target_frame and source_frame.

Raises:

tf2.ConnectivityException, tf2.LookupException, or tf2.ExtrapolationException, or tf2.InvalidArgumentException

Extended version of lookupTransform().