Guide to WMO Table Driven Code Forms

Octet No. Contents
1-4 Length of section in octets (nn)
5 Number of Section (“3”)
6 Source of grid definition (see Code Table 3.0 and Note 1)
7-10 Number of data points
11 Number of octets for optional list of numbers defining number of points (see
Note 2)
12 Interpretation of list of numbers defining number of points (see Code Table
3.11)
13-14 Grid Definition Template Number (=N) (see Code Table 3.1)
15-xx Grid Definition Template (see Template 3.N, where N is the Grid Definition
Template Number given in octets 13-14)
[xx+1]-nn Optional list of numbers defining number of points (see Notes 2, 3, and 4)
Let us assume the values in octets 6, 11, and 12 are all zero, thus eliminating the special cases
described in Section 2.1.4, and the value in octets 13 - 14 is 20. Code Table 3.1 reveals that 20
corresponds to a Polar Stereographic grid projection. It is described by Grid Definition template
3.20. We now insert Grid Definition Template 3.20 into octets 15-xx. The contents of the Grid
Definition Section then become:
Octet No. Contents
1-4 Length of section in octets (nn)
5 Number of Section (“3”)
6 Source of grid definition (see Code Table 3.0 and Note 1)
7-10 Number of data points
11 Number of octets for optional list of numbers defining number of points (see
Note 2)
12 Interpretation of list of numbers defining number of points (see Code Table
3.11)
13-14 Grid Definition Template Number (=N) (see Code Table 3.1)
15 Shape of the earth (see Code Table 3.2)
16 Scale factor of radius of spherical earth
17-20 Scaled 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 Nx – number of points along X-axis
35-38 Ny – number of points along Y-axis
39-42 La1 – latitude of first grid point
43-46 Lo1 – longitude of first grid point
47 Resolution and component flag (see flag table 3.3 and Note 1)
48-51 LaD – Latitude where Dx and Dy are specified
52-55 LoV – orientation of the grid (see note 2)
56-59 Dx – X direction grid length (see Note 3)
60-63 Dy – Y direction grid length (see Note 3)
64 Projection centre flag (see Flag Table 3.5)
65 Scanning mode (see Flag Table 3.4)
The four notes referred to in Grid Definition Template 3.20 are:
1. The resolution flag (bit 3-4 of Flag Table 3.3) is not applicable.
2. LoV is the longitude value of the meridian that is parallel to the Y-axis (or columns
of the grid) along which latitude increases as the Y-coordinate increases (the
orientation longitude may or may not appear on a particular grid).
3. Grid length is in units of 10-3 m at the latitude specified by LaD.
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