On 12/20/2009 12:54 PM, Stuart Buchanan wrote:
>> I believe
>> --metar="XXXX 012345Z 00000KT 99SM CLR 59/M01 A2992"
>> is a correct and useful example ... but somebody should double
>> check.
>
> Thanks for the example - I'll include it in the docs. My only comment is that
> I thought the temperature was in centrigrade (at least it is in the UK), so
> 59 would be quite hot (plus we use different altimeter units).
Good catch. That's why we check these things. Metar temps are
centigrade, even in the US. I should have said:
--metar="XXXX 012345Z 00000KT 99SM CLR 15/M01 A2992"
Sorry.
The altimeter setting is unambiguous; the alternative to A2992
is Q1013 with a Q (short for QNH).
Similarly if the SM is left off, the visibility is in _meters_
(not km).
I trust FG can parse the metric and non-metric items in all
combinations (although I haven't checked).
=================
As a separate issue: With rare exceptions, the largest visibility
you will see reported in a metar is 10SM (in the US) or 9999 (meters,
elsewhere).
This is a problem for real-weather fetch, because the _reported_
visibility can be significantly less than the _real_ visibility.
I have tried to think of a heuristic to solve this problem,
without success. Sometimes a report of 10SM means 10SM and
no more, but sometimes it means unlimited visibility.
In TAFs you sometimes get a forecast of P6SM which is
French for "plus que" 6SM i.e. more than 6SM. But this
does not apply to metars and doesn't solve the problem.
The FG scenery looks nice when the visibility is unlimited.
It would be a shame to stumble into a situation where typical
users were stuck with 10SM visibility instead of the really
real visibility.
This is no problem for a manually entered metar; I can enter
99SM no problem. It's just a problem for real weather fetch.
The bold solution would be to map 10SM and 9999 meters to
unlimited visibility ... but I'm not bold enough to recommend
that.
Any suggestions?
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