Grid 20: Stretched latitude/longitude
Grids
| Octets | Key | Type | Content |
| 7-8 | Ni | unsigned | Ni number of points along a parallel |
| 9-10 | Nj | unsigned | Nj number of points along a meridian |
| 11-13 | latitudeOfFirstGridPoint | signed | La1 latitude of first grid point |
| 14-16 | longitudeOfFirstGridPoint | signed | Lo1 longitude of first grid point |
| 17 | resolutionAndComponentFlags | codeflag | Resolution and component flags (see Code table 7) |
| 18-20 | latitudeOfLastGridPoint | signed | La2 latitude of last grid point |
| 21-23 | longitudeOfLastGridPoint | signed | Lo2 longitude of last grid point |
| 24-25 | iDirectionIncrement | unsigned | Di i direction increment |
| 26-27 | jDirectionIncrement | unsigned | Dj j direction increment |
| 28 | scanningMode | codeflag | Scanning mode (flags see Flag/Code table 8) |
| 29-32 | Set to zero (reserved) | ||
| 33-35 | longitudeOfStretchingPole | signed | Latitude of pole of stretching in millidegrees (integer) |
| 36-38 | latitudeOfStretchingPole | signed | Longitude of pole of stretching in millidegrees (integer) |
| 39-42 | stretchingFactor | ibmfloat | Stretching factor (representation as for the reference value) |
( 1) Latitude, longitude and increments are in millidegrees.
( 2) Latitude values are limited to the range 090 000; bit 1 is set to 1 to indicate south latitude.
( 3) Longitude values are limited to the range 0360 000; bit 1 is set to 1 to indicate west longitude.
( 4) The latitude and longitude of the last grid point and the first grid point should always be given for regular grids.
( 5) Where items are not given, the appropriate octet(s) should have all bits set to 1.
( 8) 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;
(c) The stretching factor C. The stretching is defined by representing data uniformly in a coordinate system with longitude lambda and latitude theta, where:
theta=sin-1 ( (1-C2)+(1+C2)sin theta ) / ( (1+C2)+(1-C2)sin theta )
and lambda and theta 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.
( 9) For stretched grids, the vertical coordinate parameters start at octet 43 instead of 33.
( 10) For stretched and rotated latitude/longitude grids, the vertical coordinate parameters start at octet 53.
( 11) The first and last grid points may not necessarily correspond to the first and last data points, respectively, if the bit-map section is used.
( 12) For data on a quasi-regular grid, in which all the rows or columns do not necessarily have the same number of grid points, either Ni (octets 7-8) or Nj (octets 9-10) and the corresponding Di (octets 24-25) or Dj (octets 26-27) shall be coded with all bits set to 1 (missing); the actual number of points along each parallel or meridian shall be coded.
( 13) 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 11-16. The grid points shall be evenly spaced in latitude (longitude).