Taken from a previous email to the List from Tom Kay 8/18/2001: The V&H coordinate system was/is a very imperfect formula that, when combined with the source of information fed into it by the LECs becomes a severe nightmare.
LERG (Local Exchange Routing Guide) A brief history of the system as used in the LERG: It was developed back in the '30s from an algorithm originally created in the 1500s by one of our ancient navigators (Magellan?), and only intended to work for telco purposes the continental United States. By virtue of the size of the base grid, a little bit of Southeast Alaska, parts of Canada, Mexico and some of the Carribean islands fell inside and could return 'correct' V&H for a few switches in those areas by default. The design was intended only for the United States as that was where Ma Bell operated, they had no intent or need for the system to work anywhere else. The system's design was to determine toll distances (miles) between any pair of switches, thus creating a base to determine your long distance charges. (Some of you really get shafted). The system was not designed for mapping purposes. In 1994 Bellcore (now Telcordia "http://www.telcordia.com/";) published and sold a set of computer programs to convert LL/V&H it may be available still, I have no need for it anymore so didn't look for it at the link above.) Bellcore was renamed Belllabs and then subsequently became Telcordia since the "Bell" name couldn't be used. Telcordia is currently owned by Science Applications International Corporation (SAIC). Many hundreds of the VH entries (in the LERG) are very inaccurate, frequently the LEC didn't know the coordinates (lat/lon) for a particular switch so they 'borrowed' coords from something near-by and submitted that to the LERG database via what was called the CLONES system (computer). Many other errors too are introduced with typos and other errors such as reversed input (V in the H and H in the V type errors.) To derive the greatest accuracy possible for mapping switch (device) locations, one should geocode the LERG using MapMarker plus on the street addresses and V&H on any entry that does not include a geocodeable address. (This can be done by merging LERG 1, 6 & 7 together) to put all of the relevant data together. It is a rather cumbersome task, but if you need any level of accuracy it's the best way to do it. Though you'll still have hundreds of errors. Consider that the VH system was developed without modern day computers (we had none when it was originally created) so it was the best thing available for the task. With today's GIS capabilities and computer system Bellcore should have converted their system to accept decimal degree lon/lat data instead of continuing to use V&H, or at the very least, include two columns for the original Lat/Lon pairs so that we could map them from the original source data. I approached Bellcore in 1994 about the practicallity of changing that system to dec degrees, my plea fell on deaf ears, but then 'it was they way they'd always done it', a 'legacy' system and their interest is not for mapping purposes. When one converts LL to VH the result will have an error, guaranteed. It goes without saying that if you then convert your resultant V&H pair back into lat/lons, you'll have another error. In short you will not get reliable precision from LERG data, at best you'll get close, if you need precision you can best accomplish it through development of MapBasic programs, database (LERG) merges and MapMarker+. It isn't too painful if your interest is in a small geographic area of the U.S. but for all telco switches & devices in the U.S., plan on an initial investment of a few hundred hours (program development and initial mapped results 'validation' to correct everything possible, and then a few hours each month to update your maps from LERG monthly updates. FYI... LERG data is a subset of Telcordia data. -Ross E. Bagwell GIS Manager Universal Access Inc. -----Original Message----- From: Cameron Crum [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 05, 2003 12:51 PM To: [EMAIL PROTECTED] Subject: MI-L Telephone Company Coord system I have a Telcordia(sp?), formerly Bell Labs I think, database of central offices for the US that have the fields v-coord and h-coord. The entries in these fields are a four digit number. Does anyone happen to know what coordinate system they might have used? Maybe some of the guys with a little wireline telco experience out there? Cameron --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 5798 This communication contains information from Universal Access, Inc. 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