[OSM-talk] Mapping canals

[Andy Robinson (blackadder)]

Richard Fairhurst wrote:
>Sent: 24 January 2008 3:52 PM
>To: talk at openstreetmap.org
>Subject: Re: [OSM-talk] Mapping canals
>
>Andy Allan wrote:
>
>> 2) There are two different things that everyone is talking about, and
>> keep getting them confused
>>   * The distance, or speed, that you are recording (i.e. the physical
>> property). Units are interchangable, can be converted etc to your
>> heart's content.
>>   * The manner in which the measurement is displayed in the real world
>> (i.e. the evidence, signs etc)
>
>And a third, which might sound obscure but is actually a big issue
>when we get back to canals:
>
>     * The specification of the measurement
>
>A UK narrow lock is 7ft wide. It isn't 2.14m wide.
>
>It sounds like nit-picking, but I've just typed "2.14" in because I'd
>memorised that as narrowboat-width-in-metres and that's what some of
>the brokers put in their ads.
>
>If you quote 7ft to 2 significant figures, it's 7ft. If you quote
>2.14m to 2 significant figures, it's 2.1m. There are narrowboats out
>there which will get through a 2.14m lock but not a 2.1m lock. There
>are locks (on the Chesterfield Canal) which have actually been
>built/restored too narrow because of measurement-cluelessness on the
>part of the contractors. It does happen.
>
>(Actually, on checking with a calculator, 7*12*2.54=213.36. So I'm
>doing a bit of unconscious rounding already.)
>

Indeed, the exact conversion is to multiply/divide by 0.3058 which produces
2.1336m or 2.134m if you round to the nearest millimetre.

7ft or 7' is so much simpler in this instance :-)

>Whether or not the maxwidth tag accepts measurements in feet is
>probably something that'll eventually be decided by renderer, routing
>app and editor authors, but there is certainly a need for the "7ft" to
>be recordable in the db.
>


Cheers

Andy