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NDFD Spatial Reference System



    NDFD Grids



      NDFD data are stored as points on regular grids.  There are 6 grids with each grid derived from points projected from a sphere of radius 6371.2 km.  The CONUS and Northern Hemisphere grids use a Lambert Conformal projection while the Guam, Hawaii, Puerto Rico, and Northern Pacific grids use a Mercator projection.  The Alaska grid is based on a Polar Stereographic projection.  Additional meta-data on NDFD grids are available in three grid definition tables below.

    NDFD Horizontal Datum



    NDFD Vertical Datum



      The NDFD uses elevation values referenced to mean sea level as represented by the WGS84 geoid.

    Details of NDFD Grids Found in GRIB2 Meta Data



    The NDFD grids, as described in the tables below, are the result of projecting a sphere onto a flat surface. The corner of the grid is found at the point identified in the grid parameters tables as latitude1 and longitude1. Each table lists the number of points in the grid which is the product of the number of points on the parallel and meridian. Grid points are seperated by Dx meters along the x axis (longitude) and Dy meters along the y axis (latitude). The projection type, earth radius, and other grid definition parameters are provided in the tables below. For more information on decoding GRIB2 files, see the section on GRIB2 Links.

      CONUS and Northern Hemisphere Grids

      Grid Parameter CONUS 5km CONUS 2.5km Northern Hemisphere
      Number of Points 739297 2953665 1509825
      Projection Type Lambert Conformal Lambert Conformal Lambert Conformal
      Shape of Earth sphere sphere sphere
      Earth Radius 6371.2 km 6371.2 km 6371.2 km
      Number of Points on the parallel 1073 2145 1473
      Number of Points on the Meridian 689 1377 1025
      Latitude1 20.191999 20.191999 12.189999
      Longitude1 238.445999 238.445999 226.541000
      u/v vectors relative to easterly/northerly easterly/northerly easterly/northerly
      Dx 5079.406 m 2539.703 m 5079.406 m
      Dy 5079.406 m 2539.703 m 5079.406 m
      GRIB2 grid, scan mode 64 (0100) 64 (0100) 64 (0100)
      Scan i/x direction positive positive positive
      Scan j/y direction positive positive positive
      Consecutive points in i/x direction i/x direction i/x direction
      Adjacent rows scan in same direction same direction same direction
      Mesh Latitude 25 25 25
      Orientation Longitude 265 265 265
      Which Pole is on the Plane north north north
      Is Projection Bi-polar no no no
      Tangent Latitude1 25 25 25
      Tangent Latitude2 25 25 25
      Southern Latitude -90 -90 -90
      Southern Longitude 0 0 0

      Guam, Hawaii, Puerto Rico Grids, Northern Pacific and Oceanic Grids

      Grid Parameter Guam Hawaii Puerto Rico N. Pacific Oceanic
      Number of Points 37249 72225 75936 1580529 4512981
      Projection Type Mercator Mercator Mercator Mercator Mercator
      Shape of Earth sphere sphere sphere sphere sphere
      Earth Radius 6371.2 km 6371.2 km 6371.2 km 6371.2 km 6371.2 km
      Number of Points on the parallel 193 321 339 1473 2517
      Number of Points on the Meridian 193 225 224 1073 1793
      Latitude1 12.349884 18.072699 16.977485 -25.000000 -30.4192
      Longitude1 143.686538 198.474999 291.972167 110.000000 129.906000
      u/v vectors relative to easterly/northerly easterly/northerly easterly/northerly easterly/northerly easterly/northerly
      Latitude2 16.794399 23.087799 19.544499 60.643999 79.991525
      Longitude2 148.280000 206.130999 296.015600 250.871000 10.689223
      Dx 2500.0 m 2500.0 m 1250.0 m 10000.0 m 10000.0 m
      Dy 2500.0 m 2500.0 m 1250.0 m 10000.0 m 10000.0 m
      GRIB2 grid, scan mode 64 (0100) 64 (0100) 64 (0100) 64 (0100) 64 (0100)
      Scan i/x direction positive positive positive positive positive
      Scan j/y direction positive positive positive positive positive
      Consecutive points in i/x direction i/x direction i/x direction i/x direction i/x direction
      Adjacent rows scan in same direction same direction same direction same direction same direction
      Mesh Latitude 20 20 20 20 20
      Orientation Longitude 0 0 0 0 0
      Tangent Latitude1 0 0 0 0 0
      Tangent Latitude2 0 0 0 0 0
      Southern Latitude 0 0 0 0 0
      Southern Longitude 0 0 0 0 0

      Alaska Grid

      Grid Parameter Alaska
      Number of Points 456225
      Projection Type Polar Stereographic
      Shape of Earth sphere
      Earth Radius 6371.2 km
      Number of Points on the parallel 825
      Number of Points on the Meridian 553
      Latitude1 40.530101
      Longitude1 181.429000
      u/v vectors relative to easterly/northerly
      Dx 5953.125 m
      Dy 5953.125 m
      GRIB2 grid, scan mode 64 (0100)
      Scan i/x direction positive
      Scan j/y direction positive
      Consecutive points in i/x direction
      Adjacent rows scan in same direction
      Mesh Latitude 60
      Orientation Longitude 210
      Which Pole is on the Plane north
      Is Projection Bi-polar no
      Tangent Latitude1 90
      Tangent Latitude2 90
      Southern Latitude 0
      Southern Longitude 0
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