The navigation underwent a major overhaul. This is probably the first time it's had a serious tuning since the turtlebot software first came out. We certainly never got around to it for hydro and so it was mostly running off defaults or initialisations from Turtlebot 1. See this blog post for more details.
Interactions & Remocons
Indigo introduces new ways to interact with your turtlebot via qt and android remocons.
You can find a quick guide to get started with the qt remocons in Interacting with your Turtlebot and some tutorials about developing your own robot applications and interactions in Create your First Rapp and Create your First Interaction.
The default 3D sensor is now Asus Xtion Pro.
Due to EOL of Microsoft Kinect, the default 3D sensor is now configured as Asus Xtion Pro. If you have used a Kinect for your TurtleBot, please refer Kinect Setup for kinect configuration.
Supporting two locations for Asus Xtion Pro
Indigo supports two locations for Asus Xtion Pro(asus_xtion_pro and asus_xtion_pro_offset). asus_xtion_pro is a default configuration which locates the sensor at the center. asus_xtion_pro_offset is old asus xtion pro location which is slightly located on the right. It is to keep backward compatibility for previous distributions TurtleBot(hydro, groovy) that asus xtion pro are mounted. See this pull request for more details. These are configurable via TURTLEBOT_3D_SENSOR environment variable.
Freenect as Kinect Driver
Indigo TurtleBot utilises environment variables to configure your TurtleBot settings. It allows you to configure your robot without modifying minimal.launch. See TurtleBot Environment Variables for more details.
Also note that TurtleBot Gazebo 3D Simulation is still available.