[Tagging] Feature proposal - Power transmission refinement - RFC 2
Ole Nielsen
on-osm at xs4all.nl
Wed Jul 9 19:30:10 UTC 2014
On 09/07/2014 09:44, Kytömaa Lauri wrote:
> Calling it "replacement" doesn't mean it's not "deprecation". The
> proposal is still trying to deprecate power=minor_line, and to remove
> the simple physical distinction between "really big thing on big
> pylons" vs. smaller overhead lines that you can often find
> everywhere.
>
> Mappers can make that size distinction much easier and faster than
> they could estimate what the actual voltage happens to be; the size
> is the criteria, not the voltage, even if the size quite often
> exceeds the threshold after some value in any particular country. And
> that classification is the most prominent feature for everybody else
> not interested in the voltages or circuits or number of cables or
> whatever; in mostly incomplete areas, mappers are most likely to
> first draw only the "big things", and only then start adding the
> minor_line's, so it's even easier to use the right choice. Pnorman
> provided you with nice example pictures for the distinction on the
> rendering github pages, and gravitystorm explained in detail in
> another issue in the same tracker why arbitrarily changing
> established tags is bad for the community. It should be a lesser
> inconvenience for power infrastructure consumers to select "where
> (power=line or power=minor_line) and voltage=" etc., than it would be
> for every other existing map to be cluttered with prominent power
> lines crisscrossing the suburbs and countryside until all eternity
> (entering a voltage=* tag can never be enforced on mappers).
+1
I see two problems with this proposal.
1) This proposal requires a voltage tag to distinguish "big" and "small"
power lines. If mappers don't add a voltage tag then it's probably
because they don't know the voltage and this information is often
difficult to get hand on. However, they can mostly figure out whether it
is a "major" or a "minor" power line looking at the towers/poles and use
either "line" or "minor line" appropriately. With only "power=line" as
main tag and not knowing the voltage they can't add this information
anymore.
2) The proposal will require renderers and other consumers to evaluate
the voltage tag if they want to distinguish between major and minor
lines. This can however be a rather complex task since the voltage tag
values are not always simple numerical values as required to perform
simple comparisons. In the case where two voltage separated by a
semicolon are specified more complex processing using regular
expressions etc is required. I have the feeling that the Carto
stylesheet maintainers won't be eager to implement that (if supported by
Carto at all).
The result of deprecating "minor_line" will effectively be a loss of
information in the database and in inferior rendering of power lines
(400 kilovolt lines and 400 volt lines will be rendered the same way!)
Ole
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