Hi everyone,

Here is my discussion with aliponte, as suggested by Friedrich Volkmann
I've contacted him last week end.
I've asked him before if he minds copying it here.
==

Bonjour fanfouer,

aliponte <http://www.openstreetmap.org/user/aliponte> vous a envoyé un
message depuis OpenStreetMap avec le sujet Re: Power networks :
==

Dear François,

I am pleased to read, that somebody takes me for an expert on power
facilities. But I'm just a person, who likes do reveal how things belong
together especially am I interested in in the structure of our power net.

Another interest of mine is to take care of a homogeneous discription of
equivalent objects. A good quantum of my work was scanning all power
objects in certain regions (i.e. Bavaria, Austria) and to synchronize the
tags used. I have been doing this, because a query to the OSM data base
only makes sense, if similar objects are similarly characterized.

I did not survey the discussion on reorganizing the keys of power
facilities. As far as I have seen, one aspect of the discussion is the
tagging of substations. A power substation is in electrical terms an
assembly of several switches and transformers (not only in the sense of
transforming voltages, even in the sense of frequency transforming,
including f=0, i.e. DC). Depending on the voltages used, the size of this
assambly which shall be called "substation" in the future, may be as large
as several acres or it can fit in to a garage like box. If we put the *common
task* of all these assemblies in the highest rank, we should all call them
"substations". And as we need to make a difference between their
considerable difference in size, we need to have a suitable
characteristicum. Some people suggest, we can use the highest voltage
handled by the substation. In deed, the voltage is the main parameter the
size of a transforming assembly is depending on (but not allways, as SF6
techniques allow for reducing the size of switches considerably). As I
understood the discussion, this is one of the guide lines for the renewal
of the tagging of power facilities.

On the other hand why should we shift the way of destinguishing the sizes
of substations from the top-level key "power" to a secondary key like
"voltage" (or some other suitable key)? Let us take "power=pole" and
"power=tower". Basically poles and towers are doing the same: they are
carrying wires. Their main differences are their different capabilty in
carrying more or less heavy wires and providing more or less space between
the wires. If we follow the concept of summarizing tags to a more general
one as is being proposed for substations/stations, "power=pole" has to be
substituted by "power=tower". As a consequence we have to look for a key
that gives information about the size of the tower. Which one should we
take? The height? Getting this measure will be difficult for most of us.
The length of isolators? The spacing of the wires? Or even the voltage of
the circuits the tower carries? If we delegate a differentiation from a
primary key to a sub key this tends to afford more precise information
about the object we want te describe. This is the most relevant drawback I
see when changing over to the new paradigma. As of now OSM taggers only
need to identify the course feature of an object which is sufficient to
give it a proper tag. But if a more precise feature is necessary for
correctly tagging, I am afraid the destinguishing key will be ignored or
wrong in many cases. As a consequence data base queries or map rendering
will be negativly affected. There are more examples of the kind tower/pole.
Take power=cable and power=line. The term "line" is the main term (in the
sense it is conducting electricity) and we want to destinguish those over
ground which are now being called "lines" and those under ground which are
now being called "cable". Following the new paradigma all "cables" have to
be retagged as "lines". In the days I was an OSM greenhorn, I tagged power
cables as "power=line" and "layer=-1". It didn't take long and some
experienced OSM collegues deprecated my tagging (and changed it without
informing me).

I'm not a fighter. Not for things that do not affect the quality of a
system in general. I can live with the old and will live with a new tagging
scheme. If you ask me what I'd prefer, I'd answer: Let a bot run over the
data base that converts all "power=station" to "power=substation". This is
the correct english terminus. And then tell all the OSM taggers
"sub_stations" that handle voltages below 50 kV have to be replaced by
something new, say "power_box", "power_distribution_cabinet" or something
like that and those that handle higher voltages should loose their
underspace.

Greatings Heinrich

==

*François Lacombe*

francois dot lacombe At telecom-bretagne dot eu
http://www.infos-reseaux.com
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