## ON388 - TABLE D
Sundry Grid Definitions

Revised 09/14/2006
Red text depicts changes made since 03/10/1998
LATITUDE/LONGITUDE GRIDS
INCLUDING GAUSSIAN
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Ni - No. of points along a latitude circle
9 - 10 | Nj - No. of points along a longitude meridian
11 - 13 | La1 - latitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 90,000; bit 1 (leftmost) set to 1 for south latitude
14 - 16 | Lo1 - longitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 360,000; bit 1 (leftmost) set to 1 for west longitude
17 | Resolution and component flags (See Table 7)
18 - 20 | La2 - Latitude of last grid point (same units, value range, and bit 1 as La1)
21 - 23 | Lo2 - Longitude of last grid point (same units, value range, and bit 1 as Lo1)
24 - 25 | Di - Longitudinal Direction Increment (same units as Lo1) (if not given, all bits set = 1)
26 - 27 | Regular Lat/Lon Grid: Dj - Latitudinal Direction Increment (same units as La1) (if not given, all bits set = 1) or Gaussian Grid: N - number of latitude circles between a pole and the equator Mandatory if Gaussian Grid specified
28 | Scanning mode flags (See Table 8)
29 - 32 | Reserved (set to zero)

Notes:
1) | The latitude and longitude of the first and last gridpoints should always be given, for regular grids.
2) | If a quasi-regular grid is to be described, 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).
3) | A quasi-regular grid can be defined only for rows or columns, but not both simultaneously. The first point in each row (column) shall be positioned at the meridian (parallel) indicated in octets 11-16. The grid points shall be evenly spaced in latitude (longitude).
4) | For Gaussian grids only the rows can be rendered quasi-regular; the first point shall be located at the meridian given in octets 14-16 and the last point at the meridian given in octets 21-23.

ARAKAWA SEMI-STAGGERED E-GRID
ON ROTATED LATITUDE/LONGITUDE GRID
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Ni - Total number of actual data points included on grid
9 - 10 | Nj - Dummy second dimension; set = 1
11 - 13 | La1 - latitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 90,000; bit 1 (leftmost) set to 1 for south latitude
14 - 16 | Lo1 - longitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 360,000; bit 1 (leftmost) set to 1 for west longitude
17 | Resolution and component flags (See Table 7)
18 - 20 | La2 - Number of mass points along southernmost row of grid
21 - 23 | Lo2 - Number of rows in each column
24 - 25 | Di - Longitudinal Direction Increment (same units as Lo1; value must be supplied)
26 - 27 | Dj - Latitudinal Direction Increment (same units as La1; value must be supplied)
28 | Scanning mode flags (See Table 8)
29 - 32 | Reserved (set to zero)

Note:
The rotation of the latitude/longitude grid is such that the intersection of the "prime meridian" and the "equator" has been located at the central latitude and longitude of the area represented.

ARAKAWA FILLED E-GRID ON ROTATED
LATITUDE/LONGITUDE GRID
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Ni - Total number of actual data points included on grid
9 - 10 | Nj - Dummy second dimension; set = 1
11 - 13 | La1 - latitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 90,000; bit 1 (leftmost) set to 1 for south latitude
14 - 16 | Lo1 - longitude of first grid point; units: millidegrees (degrees x 1000); values limited to range 0 - 360,000; bit 1 (leftmost) set to 1 for west longitude
17 | Resolution and component flags (See Table 7)
18 - 20 | La2 - Number of (zonal) points in each row
21 - 23 | Lo2 - Number of (meridional) points in each column
24 - 25 | Di - Longitudinal Direction Increment (same units as Lo1; value must be supplied)
26 - 27 | Dj - Latitudinal Direction Increment (same units as La1; value must be supplied)
28 | Scanning mode flags (See Table 8)
29 - 32 | Reserved (set to zero)

Note:
The rotation of the latitude/longitude grid is such that the intersection of the "prime meridian" and the "equator" has been located at the central latitude and longitude of the area represented.

POLAR STEREOGRAPHIC GRIDS
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Nx - Number of points along x-axis
9 - 10 | Ny - Number of points along y-axis
11 - 13 | La1 - Latitude of first grid point
14 - 16 | Lo1 - Longitude of first grid point
17 | Resolution and component flags (See Table 7)
18 - 20 | Lov - The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the y-axis (or columns of the grid) along which latitude increases as the y-coordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.)
21 - 23 | Dx - the X-direction grid length (see note 2)
24 - 26 | Dy - the Y-direction grid length (see note 2)
27 | Projection center flag (see note 5)
28 | Scanning mode (See Table 8)
28 | Set to 0 (reserved)

Notes:
1) | Latitude and longitude are in millidegrees (thousandths)
2) | Grid lengths are in units of meters, at the 60 degree latitude circle nearest to the pole in the projection plane.
3) | Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitude.
4) | Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
5) | Octet 27: Bit 1 set to 0 if the North pole is on the projection plane. Bit 1 set to 1 if the South pole is on the projection plane.
6) | The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.
7) | The resolution flag (bit 1 of Table 7) is not applicable.

Curvilinear Orthogonal Grids
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
7 - 8 | Ni - No. of points along x - grid direction
9 - 10 | Nj - No. of points along y - grid direction
11 - 13 | Grid Cell centered at P, U, V [p|u|v] [0|1|2] points
14 - 16 | Reserved (set to zero)
17 | Resolution & Component flags (See Table 7)
18 - 27 | Reserved (set to zero)
28 | Scanning Mode Flags (See Table 8)
29 - 32 | Reserved (set to zero)

Notes:
1) | Orthogonal on the sphere with smoothly changing grid size dx=dy. x-y-z right handed with z-positive upwards.
2) | Arakawa C-grid

LAMBERT CONFORMAL
SECANT OR TANGENT CONE GRIDS
(GDS Octets 7 - 42)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Nx - Number of points along x-axis
9 - 10 | Ny - Number of points along y-axis
11 - 13 | La1 - Latitude of first grid point
14 - 16 | Lo1 - Longitude of first grid point
17 | Resolution and component flags (See Table 7)
18 - 20 | Lov - The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the y-axis (or columns of the grid) along which latitude increases as the y-coordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.)
21 - 23 | Dx - the X-direction grid length (see note 2)
24 - 26 | Dy - the Y-direction grid length (see Note 2)
27 | Projection center flag (see note 5)
28 | Scanning mode (See Table 8)
29 - 31 | Latin 1 - The first latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8)
32 - 34 | Latin 2 - The second latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8)
35 - 37 | Latitude of southern pole (millidegrees)
38 - 40 | Longitude of southern pole (millidegrees)
41 - 42 | Reserved (set to 0)

Notes:
1) | Latitude and longitude are in millidegrees (thousandths)
2) | Grid lengths are in units of meters, at the intersection latitude circle nearest to the pole in the projection plane.
3) | Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitde.
4) | Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
5) | Octet 27: Bit 1 set to 0 if the North pole is on the projection plane. Bit 1 set to 1 if the South pole is on the projection plane. Bit 2 set to 0 if only one projection center used Bit 2 set to 1 if projection is bipolar and symmetric
6) | The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.
7) | The resolution flag (bit 1 of Table 7) is not applicable.
8) | If Latin 1 = Latin 2 then the projection is on a tangent cone.

MERCATOR GRIDS
(GDS Octets 7 - 42)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Ni - Number of points along a latitude circle
9 - 10 | Nj - Number of points along a longitude meridian
11 - 13 | La1 - Latitude of first grid point
14 - 16 | Lo1 - Longitude of first grid point
17 | Resolution and component flags (See Table 7)
18 - 20 | La2 - latitude of last grid point
21 - 23 | Lo2 - longitude of last grid point
24 - 26 | Latin - The latitude(s) at which the Mercator projection cylinder intersects the earth.
27 | Reserved (set to 0)
28 | Scanning mode (See Table 8)
29 - 31 | Di - the longitudinal direction increment (see note 2)
32 - 34 | Dj - the latitudinal direction increment (see note 2)
35 - 42 | Reserved (set to 0)

Notes:
1) | Latitude and longitude are in millidegrees (thousandths)
2) | Grid lengths are in units of meters, at the circle of latitude specified by Latin.
3) | Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitude.
4) | Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
5) | The latitude and longitude of the last grid point should always be given.
6) | The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.

SPACE VIEW PERSPECTIVE OR ORTHOGRAPHIC
(GDS Octets 7 - 44)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | Nx - number of points along x axis (columns)
9 - 10 | Ny - number of points along y axis (rows or lines)
11 - 13 | Lap - latitude of sub-satellite point
14 - 16 | Lop - longitude of sub-satellite point
17 | Resolution and component flags (See Table 7)
18 - 20 | dx - apparent diameter of earth in grid lengths, in x direction
21 - 23 | dy - apparent diameter of earth in grid lengths, in y direction
24 - 25 | Xp - X-coordinate of sub satellite point
26 - 27 | Yp - Y-coordinate of sub-satellite point
28 | Scanning Mode (See Table 8)
29 - 31 | The orientation of the grid; i.e., the angle in millidegrees between the increasing y axis and the meridian of the sub-satellite point in the direction of increasing latitude (see note 3).
32 - 34 | Nr - the altitude of the camera from the earth's center, measured in units of the earth's (equatorial) radius (See note 4).
35 - 44 | reserved

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) | Octet 32-34 shall be set to all ones (missing) to indicate the orthographic view (from infinite distance).
3) | It is the angle between increasing y axis and the meridian 180 degrees east if the sub-satellite point is the North pole; or the meridian 0 degrees, if the sub-satellite point is the south pole.
4) | The apparent angular size of the earth will be given by 2 * asin (1/Nr).
5) | The horizontal and vertical angular resolutions of the sensor (Rx and Ry), needed for navigation equations, can be calculated from the following: Rx = 2 * asin(1/Nr) / dx Ry = 2 * asin(1/Nr) / dy

SPHERICAL HARMONIC COEFFICIENTS
(GDS Octets 7 - 32)

OCTET NO. | CONTENT & MEANING
--- | ---
7 - 8 | J - Pentagonal Resolution Parameter
9 - 10 | K - Pentagonal Resolution Parameter
11 - 12 | M - Pentagonal Resolution Parameter
13 | Representation Type (See Table 9)
14 | Coefficient Storage Mode (See Table 10)
15 - 32 | Set to zero (reserved)

Office Note 388 - GRIB