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50 CHAPTER 5. RESULTS
After defining the setup of the robot, the next step is to look at the component-based system and
the components used for the application running on the robot. For the simulation the system shown
in Figure 5.2 is used. There are different components, where each component is responsible for one
device like the robot arm or a camera. The TF Data which a component provides is labeled with
a letter that corresponds to a tf frame in the tf tree. It can be seen, that some components like the
head component do provide more than one TF Data. To publish the static transformations a special
component named static transforms is implemented. The use of this special component keeps other
components which provide sensor data like the laser component free from transformations. Of course
it would also be possible to publish the static transformations by the components which provide sensor
data.
Further the system contains three components which use the TF Data and the Sensor Data provided
by the other components to fulfill tasks like collision avoidance, creating a colored 3D point
cloud or a 3D scan. The components achieve this by orchestrating other components. Control messages
like a message telling the head to pan left are not shown in the figure, because they are not
interesting for doing transformations.
only published
once to every
component
torso
static transforms
arm
h
g g e f i l a b c d
tilt
h
collision
avoidance
color 3D
point cloud
arm 3D scan
head
i k
laser
camera
arm laser
Figure 5.2: Component model with data flow. TF Data is linked by names with the tf tree.
5.1 Simulation
For the actual simulation the data flow for the collision avoidance component is used. Thus the static
transforms, the torso, the tilt, the laser and the collision avoidance component have to be modeled.
After knowing the components the tf chain, describing the transformation needed to transform the
laser scan captured in the laser_frame into the base_frame, can be determined in the tf tree.
This is done by looking for the path from the base_frame to the laser_frame. The result is
the tf chain: base_frame → torso_frame → laser_tilt_frame → laser_frame. For
the application of collision avoidance the position accuracy of the laser_frame and in particular
of a point captured by the laser ranger is of interest. Thus the simulation should answer the following
questions.
How good is the quality at the laser_frame and a point captured by the laser ranger if