GRIB2 - GRID DEFINITION TEMPLATE 3.2

Stretched Latitude/Longitude (or equidistant
cylindrical, or Plate Carree)

Revised 04/22/2013
Red text depicts changes made since 12/22/2011


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 parallel
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 4)
68-71 Dj—j direction increment (see Note 1 and 4)
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 3)


Notes:

1.  Basic 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 stretching is defined by three parameters:
      (a) The latitude in degrees (measured in the model coordinate system) of the "pole of stretching";
      (b) The longitude in degrees (measured in the model coordinate system) of the "pole of stretching"; and
      (c) The stretching factor C in units of 10-6 represented as an integer.

The stretching is defined by representing data uniformly in a coordinate system with longitudeq λ and latitude θ1, where:
        θ 1 = sin-1[(1- C2) + (1 + C2) sin θ] / [(1 + C2) + (1 - C2) sin θ ]

and λ and θ are longitude and latitude in a coordinate system in which the "pole of stretching" is the northern pole. C = 1 gives uniform resolution, while C > 1 gives enhanced resolution around the pole of stretching.

3.  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 or variable spacing. The first point in each row (column) shall be positioned
at the meridian (parallel) indicted by octets 47-54. The grid points shall be evenly spaced in latitude (longitude).

4.  It is recommended to use unsigned direction increments.


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