Thermal sources at low altitudes. Intuitively expected and actual. 

This is a function of wind speed and altitude. On a nil wind day the thermal might stay pretty close to the thermal source as it rises. On a strong wind day the source will be further upwind as it is being blown towards you as it rises.

The axis of the spiral points to the place of thermal source. If you centre the thermal correctly, you can use Google Earth to identify the source. This does not always work, but in most cases. A good lecture about thermals: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-LwSJmCGfvAo.html

​@@kurkotava801that's reasonable... by the way, how do you glue graphics to a spot in you video? Which editor/function is it?

@@kurkotava801 the lecture is a great one indeed!

@@simhathecat I use KDENlive, great freeware! You can find tutorial videos about the motion tracking effect and keyframes.