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getTransform

Return transformation between two coordinate frames

Since R2023b

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Syntax

tf = getTransform(bagReader,targetframe,sourceframe)
tf = getTransform(bagReader,targetframe,sourceframe,sourcetime)

Description

tf = getTransform(bagReader,targetframe,sourceframe) returns the latest known transformation between two coordinate frames. tf represents the transformation that takes coordinates in the initial coordinate frame into the corresponding coordinates in the target coordinate frame. The transformation tf is empty if no transformation is available between the two coordinate frames.

example

tf = getTransform(bagReader,targetframe,sourceframe,sourcetime) returns the transformation at the time sourcetime. If the transformation at that time is not available, the function returns an error.

Examples

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Open Live Script

Specify the full path to the log folder.

folderPath = fullfile(pwd,"tf_and_static_bag");

Create a ros2bagreader object that contains all the messages in the log file. 

bagReader = ros2bagreader(folderPath);
pause(1)

Use the AvailableFrames property to see the all the available transformation frames. 

frames = bagReader.AvailableFrames
frames = 8×1 cell
    {'frame1'}
    {'frame2'}
    {'frame3'}
    {'frame4'}
    {'frame5'}
    {'frame6'}
    {'frame7'}
    {'frame8'}

Use getTransform to access the latest transformation between the first and second coordinate frames.

tf2Msg = getTransform(bagReader,frames{2},frames{1})
tf2Msg = struct with fields:
       MessageType: 'geometry_msgs/TransformStamped'
            header: [1×1 struct]
    child_frame_id: 'frame1'
         transform: [1×1 struct]

Use canTransform to determine whether the transformation is available at a specific time by using ros2time. Use StartTime property to access the latest transformation between the first and second coordinate frames at that specific time.

tf2Time = ros2time(bagReader.StartTime+1);
isAvailable = canTransform(bagReader,frames{2},frames{1},tf2Time);
if isAvailable
    tf2MsgAtTime = getTransform(bagMsgs,frames{2},frames{1},tf2Time);
end

Input Arguments

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Index of messages in a ROS 2 bag, specified as a ros2bagreader object.

Target coordinate frame, specified as a string scalar or character vector. You can view the available frames for transformation by calling bagReader.AvailableFrames.

Data Types: char | string

Initial coordinate frame, specified as a string scalar or character vector. You can view the available frames for transformation by calling bagReader.AvailableFrames.

Data Types: char | string

ROS 2 or system time, specified as a scalar or structure that resembles the output of ros2time. The software converts the scalar input into structure using ros2time. By default, sourcetime corresponds to the system time. If you set the use_sim_time ROS 2 parameter to 1 (true) on the ros2node object associated with the ros2time function, sourcetime corresponds to the ROS 2 simulation time published on the /clock topic.

Data Types: struct | double

Output Arguments

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Transformation between coordinate frames, returned as a structure that represents geometry_msgs/TransformStamped. Transformations are structured as a 3-D translation (three-element vector) and a 3-D rotation (quaternion).

Data Types: struct

Version History

Introduced in R2023b

See Also

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