[Talk-TW] Taiwan Highway Shields rendering

[Arne Goetje]

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Dear all,

I'm currently in the process of hacking the rendering of Taiwan's
highway shields into Mapnik, so that we can us it on our local
rendering server. I have uploaded[1] an example screenshot of my local
server's output as illustration how it may look like in future. (Don't
worry,I will make it more beautiful. This is just a proof of concept.)

However, in order for this to work properly, I need everyone's help to
fix the 'ref' tags in the database.

1. How the 'ref' tags are used:
	a. 'ref:en' and 'ref:zh'
	These tags are *never* rendered on the map! The /may/ be used by
routing software to *announce* the turning directions to the driver.
E.g. if 'ref:en'='Provincial Highway 4', the GPS routing software
/may/ use this value to give directions, as in: "Turn right and follow
$ref:en in 200 meters!"

	b. 'ref'
	This tag is rendered on the map *as is*. Mapnik and other
applications *do not parse* the value and probably never will.
Therefore we need to make sure that this value has a usable format.
Some time ago we agreed already, that the old practice from putting
'Fwy','Hwy' and English county abbreviations in this field (because
the rendering software did not have Chinese support available at that
time) should be changed.
Now, for the highway shields to work we *must* update all 'ref' tags
to the new tagging rules:
	* Freeways, Expressways and Highways: delete the 'Fwy' or 'Hwy'.
	  E.g. 'Fwy 1' should become '1'.
	* Tertiary highways should have the Chinese county indicator and not
the English abbreviation.
	  E.g. 'TY48' should become '桃48'. Do not put spaces, dashes or
other characters in it (e.g. 縣).

	c. 'ref' where multiple highways merge
	According to the OSM wiki, we should separate tag values with ';',
like '1;4;110', where the three highways 1,4 and 110 share the same
road. However, the ';' separator will not be parsed by the rendering
engine, that means, the value '1;4;110' will appear exactly like this
on the map. This *does not* work with the highway shields.
Since we cannot parse this value in Mapnik, we need to put additional
information into the database.

I propose the following new tags:
	1. add a 'merged_highways' tag with a value of 1, 2, 3, or how many
highways are merged on this way.
	2. add tags for each 'ref', like 'ref1', 'ref2', 'ref3', etc. with
the correct values.

Example:
	'highway'='primary'
	'name'='三民路二段 (Sec. 2, Sanmin Rd.)'
	'ref'='1;4;110'
	'ref:en'='Provincial Highways 1, 4 & Route 110'
	'ref:zh'='台1、4線、110' (or whatever better way to describe it)
	'merged_highways'='3'
	'ref1'='1'
	'ref2'='4'
	'ref3'='110'
(Note: additional tags have been omitted in this example)

This way, the default OSM map will behave like usual, but our map can
properly render 3 highway shields next to each other. (The fact that
'110' is a county highway and not a provincial highway can be
determined by regular expressions in Mapnik.)

So, please everyone help to clean up the 'ref' tags in the main OSM
database:
	* remove 'Fwy', 'Hwy' and all white spaces
	* replace the English county indicators on Tertiary highways with
their proper Chinese ones, remove spaces and dashes where not appropriate
	* Where merged highways exist, update them according to the example
above, remove spaces, ensure the separator in 'ref' is a ';'.

Happy mapping! :)

Cheers and Thanks!
Arne

[1] http://people.linux.org.tw/~arne/OSM_Highway_Shields.png

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