Sources vs. Signals in Ground Truth Labeling

In the Ground Truth Labeler app, a source is the file or folder containing the data that you want to load. A signal is the data from that source that you want to label. A source can contain one or more signals.

In many cases, a source contains only one signal. Consider an AVI video file. The source is the AVI file and the signal is the video that you load from that file. Other sources that have only one signal include Velodyne^® packet capture (PCAP) files and folders that contain image or point cloud sequences.

Sources such as rosbags can contain multiple signals. Consider a rosbag named cal_loop.bag. The rosbag contains data obtained from four sensors mounted on a vehicle. The source is the rosbag file. The signals in the rosbag are sensor_msgs topics that correspond to the data from the four sensors. The topics have these names.

• /center_camera/image_color — Image sequence obtained from the center camera

• /left_camera/image_color — Image sequence obtained from the left camera

• /right_camera/image_color — Image sequence obtained from the right camera

• /velodyne_points — Point cloud sequence obtained from a Velodyne lidar sensor

This diagram depicts the relationship between the source and each of its four signals.