Changes between Version 6 and Version 7 of GridMapHorizDatum

03/10/08 16:33:59 (11 years ago)



  • GridMapHorizDatum

    v6 v7  
    2525== Initial Statement of Technical Proposal ==
    27 === Add to the "Map parameters" lists in Examples F.1 - F.8 ===
     27=== Add the following paragraphs to Appendix F before Example F.1 ===
    29  * ''semi_major_axis'' and either ''semi_minor_axis'' or ''inverse_flattening'' - Used only for ellipsoidal earth approximations.
    30  * ''earth_radius'' - Used only for spherical earth approximations.
    31  * ''longitude_of_prime_meridian'' - Optional (default = 0.0).
     29Attributes for specifying the horizontal datum are common to all grid mappings. The horizontal datum specifies a prime meridian and an ellipsoid or sphere used to approximate the shape of the earth. The prime meridian, which defines the origin from which longitude is measured, should be specified by the value of the ''longitude_of_prime_meridian'' attribute. The ''longitude_of_prime_meridian'' attribute is optional, its default value is 0.0.
     31When an ellipsoid is used to approximate the shape of the earth, it should be specified with the ''semi_major_axis'' attribute and either the ''semi_minor_axis'' attribute or the ''inverse_flattening'' attribute. When a sphere is used, it should be specified with the ''earth_radius'' attribute. If only the ''semi_major_axis'' is specified, a client should use that value as the radius of a spherical earth. If none of the four attributes are specified, a client should assume a standard spherical or ellipsoidal earth. For instance, the "GRS 1980 Authalic Sphere" (EPSG 7048) defines the earth's radius as 6371007 meters and the "GRS 1980" ellipsoid (EPSG 7019) defines the semi-major axis as 6378137 meters and the inverse flattening as 29.257222101.
     33More complete definitions of the horizontal datum attributes are given in Table F.1.
    3335=== Add the following attributes to Table F.1 ===