A challenge to solve...but some ideas
- use a raspberry Pi with camera & some available software, should work well on ceiling as well
- Placing an IR LED(s) on the body being tracked should make this easier & more accurate
- Other approaches are small body heat/temperature detectors, placed around the edges and then triangulated.
- Use 3 or more sound sensors and have the dancer carry an audio sender, preferably inaudible. By measuring the 'speed of sound/pings' , you should be able to triangulate the loation. Will require some calibration. The sound pulses or pings, at a particular frequency, could be triggered by the Arduino using IR, which then waits for the sound pings to come back and will thus reduce interference.
- You could expand by using the IR signal to synchronize the pings from multiple dancers at different time slots.
RF: As far as I know the accuracy of most RSSI approaches are poor.