(paste output here)
Q: What is the map resolution? What does that mean — how many centimeters of real space does one pixel represent?
(your answer here)
Q: What are occupied_thresh and free_thresh? What happens to cells whose probability falls between these two values?
(your answer here)
Q: What is the origin? What real-world coordinate does the bottom-left corner of the map image correspond to?
(your answer here)
Q: Which pixel shade represents walls/obstacles? Free/traversable space? Unknown areas?
(your answer here)
Q: Are there any gray (unknown) areas? Where are they, and why might those areas not have been mapped?
(your answer here)
Pixel dimensions of alic.pgm:
(paste sips or Properties output here)
Calculation:
- Pixel width: ___ × resolution ___ m/px = ___ m wide
- Pixel height: ___ × resolution ___ m/px = ___ m tall
(paste output here)
(paste output here)
Q: What topics does /cartographer_node subscribe to? What sensor data does each topic carry?
(your answer here)
Q: What topics does /cartographer_node publish? What does each output represent?
(your answer here)
ros2 topic info /scan:
(paste output here)
ros2 topic hz /scan:
(paste output here)
ros2 topic echo /scan --once (key fields only):
(paste angle_min, angle_max, range_min, range_max, and the length of the ranges array)
Q: How many nodes publish to /scan? How many subscribe to it?
(your answer here)
Q: What is the publish rate of /scan? What does this tell you about how fast the lidar updates?
(your answer here)
Q: What are angle_min and angle_max? What range of angles does the lidar cover in degrees?
(your answer here)
Q: How many values are in the ranges array? What does each value represent physically?
(your answer here)
ros2 topic info /map:
(paste output here)
ros2 topic echo /map --once (header fields only — skip the data array):
(paste info.resolution, info.width, info.height here)
Q: What node publishes to /map?
(your answer here)
Q: What is info.resolution in the live /map message? How does it compare to alic.yaml?
(your answer here)
Q: Given info.width, info.height, and info.resolution, what is the current map size in meters? (The robot hasn't moved so it will be small — that's expected.)
(your answer here)
Q: You have now seen /scan and /map as live ROS2 topics. In your own words, describe how data flows from the lidar sensor through Cartographer to produce the occupancy grid. Reference at least one topic name in your answer.
(your answer here)