GRIB2 - GRID DEFINITION TEMPLATE 3.41

Rotated Gaussian Latitude/Longitude

Revised 06/19/2008
Red text depicts changes made since 07/29/2005


Octet No. Contents
15
 Shape of the Earth (See Code Table 3.2)
16
 Scale factor of radius of spherical Earth
17-20
 Scale value of radius of spherical Earth
21
 Scale factor of major axis of oblate spheroid Earth
22-25
 Scaled value of major axis of oblate spheroid Earth
26
 Scale factor of minor axis of oblate spheroid Earth
27-30
 Scaled value of minor axis of oblate spheroid Earth
31-34
 Ni ― number of points along a paralell
35-38

Nj — number of points along a meridian

39-42
 Basic angle of the initial production domain (see Note 1)
43-46 Subdivisions of basic angle used to define extreme longitudes and latitudes, and direction increments (see Note 1)
47-50

La1 - latitude of first grid point (see Note 1)

51-54
 Lo1 - longitude of first grid point (see Note 1)
55
 Resolution and component flags (see Flag Table 3.3)
56-59

La2 - latitude of last grid point (see Note 1)

60-63

Lo2 - longitude of last grid point (see Note 1)

64-67

Di - i direction increment (see Notes 1 and 5)

68-71 N - number of paralells between a pole and the equator (see Note 2)
72 Scanning mode (flags — see Flag Table 3.4)
73-76 Latitude of the southern pole of projection
77-80
 Longitude of the southern pole of projection
81-84
 Angle of rotation of projection
85-nn

List of number of points along each meridian or parallel
(These octets are only present for quasi-regular grids as described in note 4)


Notes:
1. Basis angle of the initial production domain and subdivisions of this basic angle are provided to manage cases where the recommended unit of 10-6 degrees is not applicable to describe the extreme longitudes and latitudes, and direction increments. For these last six descriptors, the unit is equal to the ratio of the basic angle and the subdivisions number.  For ordinary cases, zero and missing values should be coded, equivalent to respective values of 1 and 106 (10-6 degrees unit).

2. The number of parallels between a pole and the Equator is used to establish the variable (Gaussian)  spacing of the parallels; this value must always be given.

3.  Three parameters define a general latitude/longitude coordinate system, formed by a general rotation of the sphere. One choice for these parameters is:
  (a) The geographic latitude in degrees of the southern pole of the coordinate system,06 for example.
  (b) The geographic longitude in degrees of the southern pole of the coordinate system,λp for example.
  (c) The angle of rotation in degrees about the new polar axis (measured clockwise when looking from the southern to the northern pole) of the coordinate system, assuming the new axis to have been obtained by first rotating the sphere through λp degrees about the geographic polar axis and then rotating through (90 + 0p) degrees so that the southern pole moved along the (previously rotated) Greenwich meridian.

4. A quasi-regular grid is only defined for appropriate grid scanning modes. Either rows or columns, but not both simultaneously, may have variable numbers of points. The first point in each row(column) shall be positioned at the meridian (parallel) indicated by Octets 47-54. The grid points shall be evenly spaced in latitude(longitude).

5. It is recommended to use unsigned direction increments.
 


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