>> >> Any suggestion on what we should recommend for the UK? > > I suggest that whatever method we use also be used for other limits, > such as maximum heights. The difference with maximum heights in the UK > is that both a height in feet and inches, and a height in metres are > often given, and they don?t convert, even to the point of metric heights > varying for the same imperial heights (though not by much). I don?t > know that this is the case for speed limits somewhere in the world, but > does suggest a scheme that allows both values would be better for the > mapper.
The reason that bridge heights do not convert is that the safety margin that is included in the height that goes on the sign is defined differently in imperial and metric. In addition, the imperial heights are rounded up to the next 3 inches. Metric heights rounded up to the next 0.1 m - and 0.1m is not equal to 3 inches. Of course the actual true height of the bridge does convert. 1 foot is exactly equal to 0.3048m - by definition Speed limits on the other hand are a limit. In a black and white version of the law, you could be prosecuted for exceeding the speed limit by any amount. There's no safety margin akin to the bridge heights. 30mph = 48.28032 km/h exactly. There's no rounding in that conversion. The mile is defined as exactly 1.609344 km We should therefore: Use maxspeed=30 mph. (It should be trivial for any pre-processing of data to get this in the right format for whatever application it is required) *or* use maxspeed=48.28032 maxspeed=48 is wrong - you are legally allowed to travel faster - so hence it is not a maxspeed. Maxspeed=48.3 is also wrong - as the true maxspeed is lower than that. _______________________________________________ Talk-GB mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-gb
