[OSM-talk] Metric / imperial bridge heights

[Philip Homburg]

In your letter dated Sat, 11 Oct 2008 12:57:18 +0100 you wrote:
>In the UK with bridge heights there isn't an exact conversion factor - 
>mainly because a signed 11'3" bridge isn't 11'3" high. To get the signed 
>height - you subtract 3 inches from the true height then round down to the 
>next 3 inches. There will always be between 3 and 6 inches leeway.
>
>When a UK bridge is signed in metric as well, you don't convert the imperial 
>measure. You subtract 0.08m from the correct height measured in metres - and 
>then round down to 1 decimal place. Thus the actual leeway will be between 
>8cm and 18cm.

Isn't that just conservative engineering? You make sure that any verhicle that
is at most the posted height can pass safely, and when a verhicle does hit the
ceiling, you know that it was not a just a tolerance issue. There is no need
to make use of that information unless you actually have to (if there is no
other way of reaching a destination)

I guess that for routing you want to take the higher imperial heigh into
account and put the metric value in a comment section. 

Do people actually enter 11'3" in a consistent way when tagging heights?