* LeeE -- Monday 11 February 2008: > It'll be interesting if you can come up with rules or a formulae > from your analysis of a large set of METAR data.
Formulae is an overstatement. :-) What I have ATM is very simple: http://members.aon.at/mfranz/humid_vis.png [14.0 kB] Whereby the maximum (and with it the slope of the line) should be configurable and default to 80 or something. This would only be used if a data set contains "farther than x km". The values are just too unprecise for anything more sophisticated. The (simple) humidity calculation has gaps (A, B) because the temperatures are stated as integers, and many/most of the visibility ranges are probably estimated by the weather guy/gal, and very often just say ">10km". This can be anything, as the estimation isn't possible everywhere, or people only use a few reference points (as in "radio tower clearly visible => more than 10km"). The horizontal bands are at 10 km, 5 miles, 10 miles 15 miles, etc. (C, D). The problem is also that very dry places are likely more dusty, and that airports are often near bigger cities so that visibility values are influenced a lot by smog. That's why the red line looks a bit (and *is* a bit) arbitrary, and why I will *again* use a conservative default setting. :-) One effect that could also be considered is wind speed. ~7 m/s seems to give best visibility. (Less allows smog accumulation, more causes more dust.) I found the effect mentioned in some google hits, albeit without number. m. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
