GRIB2 - GRID TEMPLATE 3.90
Space view perspective or orthographic
Created 07/29/2005

Octet | Contents
--- | ---
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 (columns)
35-38 | Ny ― number of points along y-axis (rows or lines)
39-42 | Lap ― latitude of sub-satellite point
43-46 | Lop ― longitude of sub-satellite point
47 | Resolution and component flags (see Flag table 3.3)
48-51 | dx ― apparent diameter of Earth in grid lengths, in x-direction
52-55 | dy ― apparent diameter of Earth in grid lengths, in y-direction
56-59 | Xp― x-coordinate of sub-satellite point (in units of 10-3 grid length expressed as an integer)
60-63 | Yp ― y-coordinate of sub-satellite point (in units of 10-3 grid length expressed as an integer)
64 | Scanning mode (flags ― see Flag table 3.4)
65-68 | Orientation of the grid; i.e. the angle between the increasing y-axis and the meridian of the sub-satellite point in the direction of increasing latitude (see Note 3)
69-72 | Nr ― altitude of the camera from the Earth's centre, measured in units of the Earth's (equatorial) radius multiplied by a scale factor of 106 (see Notes 4 and 5)
73-76 | Xo ― x-coordinate of origin of sector image
77-80 | Yo ― y-coordinate of origin of sector i

Notes: 1. It is assumed that the satellite is at its nominal position i.e. it is looking directly at its sub-satellite point. 2. Octets 69-72 shall be set to all ones (missing) to indicate the orthographic view (from infinite distance). 3. It is the angle between the increasing y-axis and the meridian 180° E if the sub-satellite point is in the North Pole; or the meridian 0° if the sub-satellite point is the South Pole. 4. The apparent angular size of the Earth will be given by 2 × arcsin ((106 )/Nr). 5. For orthographic view from infinite distance, the value of Nr should be encoded as missing (all bits set to 1). 6. The horizontal and vertical angular resolutions of the sensor (Rx and Ry), needed for navigation equation, can be calculated from the following: Rx = 2 × arcsin ((106 )/Nr)/dx Ry = 2 × arcsin ((106 )/Nr)/dy

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