On Sunday, July 14, 2013 7:28:17 PM UTC-7, son_of_flubber wrote:
On Sunday, July 14, 2013 2:08:50 PM UTC-4, jfitch wrote:

Got a question: the Butterfly wind vector and the XCSoar wind vector (derived from Butterfly information) seem to disagree by 180 degrees. That is they point toward each other. XCSoar seems to believe it too, based on glide calculations.



Could you please confirm that you are saying that when XCSoar uses wind data from Butterfly Vario that it calculates glide based on the exact opposite of the correct wind vector? If so, that is a rather serious defect and you should report it to XCSoar.org pronto.

Yes - actually it seems to compute correctly, just that the Butterfly and XCSoar don't agree on which way the wind is blowing. I think. Can you confirm that the arrow in XCSoar points the direction the wind is blowing (as distinct from pointing into the wind)? What I thought I was seeing was an increase in tailwind component reported by the Butterfly increased my glide range on the Butterfly, and reduced it in XCSoar. Consistent, given that the arrows seem to be backwards. I don't know if that is an XCSoar bug or a Butterfly bug. The wind is coming from the Butterfly via LX sentence protocol.

The Butterfly computes wind VERY rapidly from the ISU. This was interesting in the rough thermals on Saturday. Not uncommon to feel a strong side gust, look at the Butterfly and see it report a very large wind vector change in response. It is unclear how this is smoothed for glide calcs, but maybe not at all - XCSoar always followed the Butterfly vector exactly, just 180 degrees out on direction.

I will report it as soon as they let me in the door.....