Changes between Version 2 and Version 3 of GridMapHorizDatum


Ignore:
Timestamp:
03/06/08 12:13:13 (11 years ago)
Author:
edavis
Comment:

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  • GridMapHorizDatum

    v2 v3  
    2727=== Add to the "Map parameters" lists in Examples F.1, F.2, F.3, F.4, F.5, F.7, and F.8 ===
    2828
    29  * semi_major_axis (use with semi_minor_axis or inverse_flattening)
    30  * semi_minor_axis
    31  * inverse_flattening
    32  * earth_radius (used in place of the above three attributes for spherical earth)
    33  * longitude_of_prime_meridian
     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.
    3432
    3533=== Add the following attributes to Table F.1 ===
    3634
    3735|| '''Attribute''' || '''Description''' ||
    38 || earth_radius || Used to specify the radius, in metres, of the spherical figure used to approximate the shape of the Earth. This attribute should be specified for those projected CRS's in which the X-Y cartesian coordinates have been derived using a spherical Earth approximation. If the cartesian coordinates were derived using the ellipsoid associated with the geodetic datum then this attribute should not be defined. Example: "6371007” , which is the radius of the GRS 1980 Authalic Sphere. ||
    39 || inverse_flattening || Used to specify the inverse flattening (1/f) of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. The flattening (f) of the ellipsoid is related to the semi-major and semi-minor axes by the formula f = (a-b)/a. In the case of a spherical Earth this attribute should be omitted. Example: 298.257222101 for the GRS 1980 ellipsoid. (Note: By convention the dimensions of an ellipsoid are specified using either the semi-major and semi-minor axis lengths, or the semi-major axis length and the inverse flattening. If all three attributes are specified then the supplied values must be consistent with the aforementioned formula.) ||
     36|| earth_radius || Used to specify the radius, in metres, of the spherical figure used to approximate the shape of the Earth. This attribute should be specified for those projections in which the X-Y cartesian coordinates have been derived using a spherical Earth approximation. If the cartesian coordinates were derived using an ellipsoid to approximate the shape of the Earth, then this attribute should not be defined. Example: "6371007” , which is the radius of the GRS 1980 Authalic Sphere. ||
     37|| inverse_flattening || Used to specify the inverse flattening (1/f) of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. The flattening (f) of the ellipsoid is related to the semi-major and semi-minor axes by the formula f = (a-b)/a. In the case of a spherical Earth this attribute should be omitted (see the ''earth_radius'' attribute). Example: 298.257222101 for the GRS 1980 ellipsoid. (Note: By convention the dimensions of an ellipsoid are specified using either the semi-major and semi-minor axis lengths, or the semi-major axis length and the inverse flattening. If all three attributes are specified then the supplied values must be consistent with the aforementioned formula.) ||
    4038|| longitude_of_prime_meridian || Specifies the longitude, with respect to Greenwich, of the prime meridian associated with the geodetic datum. The prime meridian defines the origin from which longitude values are determined. Domain: -180.0 <= longitude_of_prime_meridian < 180.0 decimal degrees. Default = 0.0 ||
    41 || semi_major_axis || Specifies the length, in metres, of the semi-major axis of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. Commonly denoted using the symbol “a”. In the case of a spherical Earth approximation this attribute defines the radius of the Earth. See also the inverse_flattening attribute. ||
    42 || semi_minor_axis || Specifies the length, in metres, of the semi-minor axis of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. Commonly denoted using the symbol “b”. In the case of a spherical Earth approximation this attribute should be omitted (the preferred option) or else set equal to the value of the semi_major_axis attribute. See also the inverse_flattening attribute. ||
     39|| semi_major_axis || Specifies the length, in metres, of the semi-major axis of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. Commonly denoted using the symbol “a”. In the case of a spherical Earth approximation this attribute should be omitted (see the ''earth_radius'' attribute). See also the ''inverse_flattening'' attribute. ||
     40|| semi_minor_axis || Specifies the length, in metres, of the semi-minor axis of the ellipsoidal figure associated with the geodetic datum and used to approximate the shape of the Earth. Commonly denoted using the symbol “b”. In the case of a spherical Earth approximation this attribute should be omitted (see the ''earth_radius'' attribute). See also the ''inverse_flattening'' attribute. ||