Thermals
Thermals in an IGC file: how to spot them after the flight
July 11, 2026
A thermal is not visible in the IGC file — what you see is what your paraglider did inside it. Post-flight analysis is about reading those footprints.
What footprint does a thermal leave in the trace?
In the track a climb shows three signs: altitude increasing for more than a few seconds, the trajectory wrapping into circles, and the circles drifting with the wind.
An IGC file records position and altitude point by point: line them up and the climbs emerge on their own.
How does RSFly.app highlight them?
RSFly.app detects the climbs directly from the flight trace and shows them in the 3D replay and in the flight analysis, with altitude gain and climb rate for each one.
On the thermal map, climbs from flights shared by the community become a browsable layer: not a forecast, but the collective memory of where the air has already worked.
Does yesterday’s thermal count tomorrow too?
No — and whoever promises otherwise is selling smoke. A spot that worked yesterday is statistical information, not a forecast: conditions, season, wind and time of day change everything.
Use post-flight analysis to understand your own climbing behaviour and to learn which slopes work most often; the decision in the air remains yours, with the usual safety rules.
In short
- A climb in an IGC file shows as rising altitude, circles, and wind drift.
- RSFly.app highlights the climbs of your flight with gain and climb rate, inventing nothing.
- Past thermals are useful statistics, never a forecast: the decision in the air belongs to the pilot.