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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