Augmented reality enhances one’s current perception of reality, whereas in contrast, virtual reality replaces the real world with a simulated one. Mobile VR is VR that is using a mobile phone as the primary viewing device (display), often with a headset like Google Cardboard or others.
C++ and Qt is a good choice for developing a mobile application, especially when you need at least two versions for different platforms. But this way is not yet too popular. Why, you may ask? Well, because there are IDEs like Android Studio, SmartCode, Xcode. It is natural to think that a native application is better than cross platform software.
Indoor navigation is a direction that is interesting for a wide range of technologies, from cybersecurity to SCADA systems. The main challenge is how to organize precisely moving or tracking some object inside a building where is no GPS signal.