What is the difference between next_command, command_near, and command_far

Hi, thanks for your great job!

I noticed three commands in the anno files and found that only 'command_near' is employed for navigation. Referring to #issue 34, 'command_near' and 'command_far' are waypoint commands for distances of 4.0m and 7.5m, respectively. So what is the meanning of 'next_command' and how can I define 'next_command' in code?