getTransform

This example shows how to set up a ROS transformation tree and transform frames based on transformation tree information. It uses time-buffered transformations to access transformations at different times.

Create a ROS transformation tree. Use rosinit to connect to a ROS network. Replace ipaddress with your ROS network address.

ipaddress = '192.168.17.129';
rosinit(ipaddress,11311)

Initializing global node /matlab_global_node_14346 with NodeURI http://192.168.17.1:56312/

tftree = rostf;
pause(1)

Look at the available frames on the transformation tree.

tftree.AvailableFrames

ans = 36×1 cell
    {'base_footprint'            }
    {'base_link'                 }
    {'camera_depth_frame'        }
    {'camera_depth_optical_frame'}
    {'camera_link'               }
    {'camera_rgb_frame'          }
    {'camera_rgb_optical_frame'  }
    {'caster_back_link'          }
    {'caster_front_link'         }
    {'cliff_sensor_front_link'   }
    {'cliff_sensor_left_link'    }
    {'cliff_sensor_right_link'   }
    {'gyro_link'                 }
    {'mount_asus_xtion_pro_link' }
    {'odom'                      }
    {'plate_bottom_link'         }
    {'plate_middle_link'         }
    {'plate_top_link'            }
    {'pole_bottom_0_link'        }
    {'pole_bottom_1_link'        }
    {'pole_bottom_2_link'        }
    {'pole_bottom_3_link'        }
    {'pole_bottom_4_link'        }
    {'pole_bottom_5_link'        }
    {'pole_kinect_0_link'        }
    {'pole_kinect_1_link'        }
    {'pole_middle_0_link'        }
    {'pole_middle_1_link'        }
    {'pole_middle_2_link'        }
    {'pole_middle_3_link'        }
      ⋮

Check if the desired transformation is now available. For this example, check for the transformation from 'camera_link' to 'base_link'.

canTransform(tftree,'base_link','camera_link')

ans = logical
   1

Get the transformation for 3 seconds from now. The getTransform function will wait until the transformation becomes available with the specified timeout.

desiredTime = rostime('now') + 3;
tform = getTransform(tftree,'base_link','camera_link',...
                     desiredTime,'Timeout',5);

Create a ROS message to transform. Messages can also be retrieved off the ROS network.

pt = rosmessage('geometry_msgs/PointStamped');
pt.Header.FrameId = 'camera_link';
pt.Point.X = 3;
pt.Point.Y = 1.5;
pt.Point.Z = 0.2;

Transform the ROS message to the 'base_link' frame using the desired time previously saved.

tfpt = transform(tftree,'base_link',pt,desiredTime);

Optional: You can also use apply with the stored tform to apply this transformation to the pt message.

tfpt2 = apply(tform,pt);

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_14346 with NodeURI http://192.168.17.1:56312/

This example shows how to access time-buffered transformations on the ROS network. Access transformations for specific times and modify the BufferTime property based on your desired times.

Create a ROS transformation tree. Use rosinit to connect to a ROS network. Replace ipaddress with your ROS network address.

ipaddress = '192.168.17.129';
rosinit(ipaddress,11311)

Initializing global node /matlab_global_node_78006 with NodeURI http://192.168.17.1:56344/

tftree = rostf;
pause(2);

Get the transformation from 1 second ago.

desiredTime = rostime('now') - 1;
tform = getTransform(tftree,'base_link','camera_link',desiredTime);

The transformation buffer time is 10 seconds by default. Modify the BufferTime property of the transformation tree to increase the buffer time and wait for that buffer to fill.

tftree.BufferTime = 15;
pause(15);

Get the transformation from 12 seconds ago.

desiredTime = rostime('now') - 12;
tform = getTransform(tftree,'base_link','camera_link',desiredTime);

You can also get transformations at a time in the future. The getTransform function will wait until the transformation is available. You can also specify a timeout to error if no transformation is found. This example waits 5 seconds for the transformation at 3 seconds from now to be available.

desiredTime = rostime('now') + 3;
tform = getTransform(tftree,'base_link','camera_link',desiredTime,'Timeout',5);

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_78006 with NodeURI http://192.168.17.1:56344/

Get transformations from rosbag (.bag) files by loading the rosbag and checking the available frames. From these frames, use getTransform to query the transformation between two coordinate frames.

Load the rosbag.

bag = rosbag('ros_turtlesim.bag');

Get a list of available frames.

frames = bag.AvailableFrames;

Get the latest transformation between two coordinate frames.

tf = getTransform(bag,'world',frames{1});

Check for a transformation available at a specific time and retrieve the transformation. Use canTransform to check if the transformation is available. Specify the time using rostime.

tfTime = rostime(bag.StartTime + 1);
if (canTransform(bag,'world',frames{1},tfTime))
    tf2 = getTransform(bag,'world',frames{1},tfTime);
end

Get transformations from rosbag (.bag) files by loading the rosbag and checking the available frames. From these frames, use getTransform to query the transformation between two coordinate frames.

Load the rosbag.

bagMsgs = rosbagreader("ros_turtlesim.bag")

bagMsgs = 
  rosbagreader with properties:

           FilePath: '/tmp/Bdoc24b_2725827_1911022/tpd3d2b8ed/ros-ex81142742/ros_turtlesim.bag'
          StartTime: 1.5040e+09
            EndTime: 1.5040e+09
        NumMessages: 6089
    AvailableTopics: [6x3 table]
    AvailableFrames: {2x1 cell}
        MessageList: [6089x4 table]

Get a list of available frames.

frames = bagMsgs.AvailableFrames

frames = 2x1 cell
    {'turtle1'}
    {'world'  }

Get the latest transformation between two coordinate frames.

tf = getTransform(bagMsgs,'world',frames{1})

tf = 
  ROS TransformStamped message with properties:

     MessageType: 'geometry_msgs/TransformStamped'
          Header: [1x1 Header]
       Transform: [1x1 Transform]
    ChildFrameId: 'turtle1'

  Use showdetails to show the contents of the message

Check for a transformation available at a specific time and retrieve the transformation. Use canTransform to check if the transformation is available. Specify the time using rostime.

tfTime = rostime(bagMsgs.StartTime + 1);
if (canTransform(bagMsgs,'world',frames{1},tfTime))
    tf2 = getTransform(bagMsgs,'world',frames{1},tfTime);
end