может поможет, только вчера искал, правда немного другое:
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* Three shift parameters specifying the distance, in meters, to shift the ellipsoid along each of its axes. These parameters are usually denoted by dX, dY, and dZ. They may also be denoted by X, Y, and Z, or by u, v, and w.
* Three rotation parameters specifying the angle, in arc-seconds, to rotate the ellipsoid around each of its axes. These parameters are usually denoted by EX, EY, and EZ. They may also be denoted by X, Y, and Z, or by , , and .
* A scale correction factor specifying the amount, in parts per million, to adjust the size of the ellipsoid. This parameter is denoted by the letter m, or sometimes .
* The longitude of the prime meridian, in degrees east of Greenwich. The prime meridian specifies which location on earth is assigned longitude 0°. Most datums use Greenwich as the prime meridian, so this parameter is usually zero. However, some datums use a different location as the prime meridian. For example, the NTF datum uses Paris as its prime meridian, which is 2.33722917 degrees east of Greenwich. If the NTF datum is used in a coordinate system, all longitudes in that coordinate system are relative to Paris instead of Greenwich.
A custom datum can be defined in any coordinate system definition. The Appendix describes how to define a coordinate system. To define a custom datum in a coordinate system, use datum number 9999 followed by the datum parameters, in this order:
9999, EllipsoidNumber, dX, dY, dZ, EX, EY, EZ, m, PrimeMeridian
Some datums specify only an ellipsoid and shift parameters (dX, dY, dZ), with no rotation parameters, scale correction, or prime meridian. In those cases, use datum number 999 instead of 9999, to simplify the definition: (See Example LD-3 below):
999, EllipsoidNumber, dX, dY, dZ