add gif of empty world visualization

doc/1_world_visualization/1_world_visualization.md

@@ -231,4 +231,57 @@ Finally, this "draw" method is defined to execute simulation including updating
 ```
 
 ## 1.2 Visualize empty world
-I prepared for [a sample progoram to visualize an empty world](/doc/1_world_visualization/visualize_world.py). You will be able to understand how to use the above world visualization class by reading the code. By executing this, you can see that an empty world simulation is visualized as follow.  
+I prepared for [a sample progoram to visualize an empty world](/doc/1_world_visualization/visualize_world.py).  
+```python
+"""
+visualize_world.py
+
+Author: Shisato Yano
+"""
+
+# import path setting
+import numpy as np
+import sys
+from pathlib import Path
+
+abs_dir_path = str(Path(__file__).absolute().parent)
+relative_path = "/../../src/components/"
+
+sys.path.append(abs_dir_path + relative_path + "visualization")
+
+
+# import component modules
+from global_xy_visualizer import GlobalXYVisualizer
+from min_max import MinMax
+from time_parameters import TimeParameters
+
+
+# flag to show plot figure
+# when executed as unit test, this flag is set as false
+show_plot = True
+
+
+def main():
+    """
+    Main process function
+    """
+
+    # set simulation parameters
+    x_lim, y_lim = MinMax(-30, 30), MinMax(-30, 30)
+    vis = GlobalXYVisualizer(x_lim, y_lim, TimeParameters(span_sec=20))
+
+    # add objects here
+
+    # plot figure is not shown when executed as unit test
+    if not show_plot: vis.not_show_plot()
+
+    # show plot figure
+    vis.draw()
+
+
+# execute main process
+if __name__ == "__main__":
+    main()
+```
+You will be able to understand how to use the above world visualization class by reading the code. By executing this, you can see that an empty world simulation is visualized as follow.  
+![](/doc/1_world_visualization/visualize_world.gif)