# V and H Coordinates

The V and H coordinate system is used in many telephone databases to geographic location.

Jay K. Donald of AT&T created the V&H coordinate system in 1957 to simplify the calculation of distance between telephone rate centers. The system is based on Donald Elliptic Projection. It is a two-point equidistant projection for the continental United States and Canada. It uses units of the square-root of one-tenth of a mile. The system was designed allow calculations in the field using a slide-rule.

To calculate the distances between a point 1 and 2 each with V and H coordinates use this formula:

Distance in miles = square_root( ( (V1-V2)**2 + (H1-H2)**2 ) /10 )

Converting from V and H to or from Latitude and Longitude appears not to be simple.

Here are some links that have source code and commentary on the conversion process

There are also a number of products you can purchase that have functions to do the conversion.

Jay K. Donald of AT&T created the V&H coordinate system in 1957 to simplify the calculation of distance between telephone rate centers. The system is based on Donald Elliptic Projection. It is a two-point equidistant projection for the continental United States and Canada. It uses units of the square-root of one-tenth of a mile. The system was designed allow calculations in the field using a slide-rule.

To calculate the distances between a point 1 and 2 each with V and H coordinates use this formula:

Distance in miles = square_root( ( (V1-V2)**2 + (H1-H2)**2 ) /10 )

Converting from V and H to or from Latitude and Longitude appears not to be simple.

Here are some links that have source code and commentary on the conversion process

- http://openmap.bbn.com has a VHTransform Class in Java
- Mailing list posting with C code
- More C code
- Mailing list posting with Fortran code
- Telcordia has a 190 page document (for sale) on the history and mathematics underlying the V and H system titled: Telcordia® Notes on V&H Coordinates: The Mystery Unveiled
- Geo::Coordinates::VandH Perl code is available from CPAN or downloadable from here
- PHP functions for VandH Calculate the distance between two VH coordinates, or convert them to lat long.

There are also a number of products you can purchase that have functions to do the conversion.

- V and H Toolkit from HTLT
- CO Finder from Stuff Software
- V&H Coordinate Batch Conversion from Quentin Sager Consulting
- VHCalc from Telcordia

## See Also

- Telcordia page on V and H Coordinates
- Map Coordinate Systems - see section on V and H in the Miscellaneous Systems section
- Online Central Office Distance Calculator

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