Visibility shows wrong unit when SM are parsed

[hvolkmer]

Repro:

Taking the example metar:

metar_string = "KHWD 280554Z AUTO 29007KT 10SM OVC008 14/12 A3002 RMK AO2 SLP176 T01390117 10211\n"
raw    = Metar::Raw::Metar.new(metar_string)
parser = Metar::Parser.new(raw)
parser.visibility.distance
 => #<Metar::Data::Distance:0x007fdab0977df8 @units=:miles, @value=16093.44> 

This is wrong/unexpected. It either needs to be

 => #<Metar::Data::Distance:0x007fdab0977df8 @units=:miles, @value=10000.00> 

or

 => #<Metar::Data::Distance:0x007fdab0977df8 @units=:meters, @value=16093.44> 

The bug seems to be in
https://github.com/joeyates/metar-parser/blob/master/lib/metar/data/visibility.rb#L20
https://github.com/joeyates/metar-parser/blob/master/lib/metar/data/visibility.rb#L27
https://github.com/joeyates/metar-parser/blob/master/lib/metar/data/visibility.rb#L33

When I try

Metar::Data::Distance.miles(10)
 => #<Metar::Data::Distance:0x007fdab08e6088 @units=:meters, @value=16093.44>

it is correct. It seems as if the units=:miles is unnecessary. This is not caught by the specs.

[joeyates]

Hello,

Sorry for the very late reply.

Due to the way that this gem handles values, based on the way the 'm9t' gem works, I think this is more a naming problem than a bug.

Internally, all values are held as SI units (with a slight variation for temperatures). So, distances will always be held as meters.

The instance variable @units is there to store the desired units to use in .to_s.

I'm going to change to name of the variable to .serialization_units in order to avoid this confusion.

[joeyates]

I've released version 1.4.0 with the update.