| Octet No. | 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 7. A scale value of radius of spherical Earth, or major or minor axis of oblate spheroid Earth, is derived by applying the apropriate scale factor to the value expressed in meters. 8. General reference information pertaining to the projections used for satellite data can be found in Section 4.4 of "LRIT/HRIT Global Specification", Doc. No. CGMS 03, issue 2.6, dated 12 August, 1999 (http://www.eumetsat.int/Home/Main/AboutEUMETSAT/ International Relations/CGMS/groups/cps/documents/document/pdf_cgms_03.pdf, page 20 onwards). |