686 lines
23 KiB
HTML
686 lines
23 KiB
HTML
<!DOCTYPE html PUBLIC "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type"
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content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR"
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content="Mozilla/4.79 [en] (X11; U; Linux 2.4.9-34smp i686) [Netscape]">
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<title>netCDF Format</title>
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</head>
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<body alink="#ff0000" bgcolor="#ffffff" link="#0000ee" text="#000000"
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vlink="#551a8b">
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<h1>
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netCDF File Format</h1>
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January 3, 2012
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<br>
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<hr width="100%">
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<br>
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This document describes the format of the netCDF file that is:
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<ul>
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<li>
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generated from the <a href="ifpnetCDF.html">ifpnetCDF product formatter</a></li>
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<li>
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read by the <a href="iscMosaic.html">iscMosaic program</a></li>
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</ul>
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In AWIPS1 ifpServer read netCDF files for gridded data. In AWIPS2 this format
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has been replaced with <a href="edexHDF5.html">HDF5 format</a>.
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<p><a href="#OrganizationoftheGriddedData">Organization of the Gridded
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Data in the netCDF file</a>
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<br>
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<a href="#netCDFVariableNames">netCDF Variable Names</a>
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<br>
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</p>
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<hr width="100%">
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<h2><a name="OrganizationoftheGriddedData"></a>Organization of the
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Gridded
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Data in the netCDF file</h2>
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<div style="margin-bottom: 0in;">To fully understand this
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section
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you should know something about how netCDF files are structured in
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general.
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See the netCDF web site at:</div>
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<div style="margin-bottom: 0in;">http://www.unidata.ucar.edu/packages/netcdf/</div>
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<div style="margin-bottom: 0in;">Each of the supported data types
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(SCALAR,
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VECTOR, and WEATHER) are stored in a slightly different way. All
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of the data types are stored as a cube as</div>
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<div style="margin-bottom: 0in;">illustrated by the figure below:</div>
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<img src="images/ifpnetCDF1.gif" name="Graphic1" border="0" height="183"
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width="285">
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<br>
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<p>For weather elements of type SCALAR, all of the data are stored in
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this
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simple cube form. For VECTOR weather elements, two cubes
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are
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used, one for the magnitude, one for direction and they are coordinated
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so that the first magnitude grid corresponds to the first direction
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grid,
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and so on. For WEATHER, one cube is used to store byte values
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that map into another structure that holds strings that represent the
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weather
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values. The following illustration shows how this WEATHER grid
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and WEATHER KEY should be used to extract a weather value.
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</p>
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<p><img src="images/ifpnetCDF2.gif" name="Graphic2" border="0"
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height="167" width="429"></p>
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<p>The grid on the left illustrates the values of the byte values for
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the
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weather grid. The list on the left shows the actual weather
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values
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expressed
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as a text string. In order to determine what the weather value
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is at any given point, you will need both the weather byte grid and the
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"weather
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key". Simply read the byte value in the grid and lookup that
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value in the key list.
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</p>
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<hr width="100%">
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<h2><a name="netCDFVariableNames"></a>netCDF Variable Names</h2>
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Each netCDF variable name represents a weather element set of grids,
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plus
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additional information:
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<br>
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<br>
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<table nosave="" border="1" width="100%">
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<caption><br>
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</caption><tbody>
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</tbody>
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<tbody>
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<tr nosave="">
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<td nosave=""><b>Format</b></td>
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<td><b>Example</b></td>
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<td><b>Data Type</b></td>
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<td><b>Dimensions</b></td>
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<td><b>Description</b></td>
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</tr>
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<tr>
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<td>parmName_level</td>
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<td>Sky_SFC</td>
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<td>Scalar Grid Data</td>
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<td>(#grids, ysize, xsize)</td>
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<td>Variable that contains scalar grids as floats, shorts, or
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bytes. Attributes
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are associated with this variable.</td>
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</tr>
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<tr>
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<td>parmName_level_GridHistory</td>
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<td>Sky_SFC_GridHistory</td>
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<td>Grid Data History for scalar, vector, and weather</td>
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<td>(# grids, string size)</td>
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<td>Variable that contains the coded grid data history for the
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grid.
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The associated grid is specified in the first dimension. The data
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format
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is characters. More detail on the formatting of the history string is
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shown
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<a href="#History">here</a>
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.</td>
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</tr>
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<tr>
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<td>parmName_Mag_level</td>
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<td>Wind_Mag_SFC</td>
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<td>Vector Grid Data, magnitude component</td>
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<td>(#grids, ysize, xsize)</td>
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<td>Variable that contains the magnitude component of the gridded
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data
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as floats, shorts, or bytes. Attributes are associated with this
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variable.</td>
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</tr>
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<tr>
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<td>parmName_Dir_level</td>
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<td>Wind_Dir_SFC</td>
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<td>Vector Grid Data, direction component</td>
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<td>(#grids, ysize, xsize)</td>
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<td>Variable that contains the direction component of the gridded
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data
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as floats, shorts, or bytes. Attributes are associated with this
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variable. The direction is the "from" direction of the wind and
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is
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in degrees from true north.</td>
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</tr>
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<tr>
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<td>parmName_level</td>
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<td>Wx_SFC</td>
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<td>Weather Grid Data</td>
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<td>(#grids, ysize, xsize)</td>
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<td>Variable that contains the weather grid as bytes. Attributes
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are associated
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with this variable. You need the weather keys to determine the meaning
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of each number in the grid.</td>
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</tr>
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<tr>
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<td>parmName_SFC_wxKeys</td>
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<td>Wx_SFC_wxKeys</td>
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<td>Weather Key Data</td>
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<td>(#grids, #keys, #size of each key)</td>
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<td>Variable that contains the weather key mapping for each Wx
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grid.
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The #keys refers to the key mapping index in the grid data.</td>
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</tr>
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</tbody>
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</table>
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<hr width="100%">
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<h2><a name="WeatherElementAttributes"></a>Weather Element Attributes</h2>
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<div style="margin-bottom: 0in;">Every Weather Element variable in the
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netCDF file has a collection of attributes. In the table below,
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we
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briefly describe each attribute and its meaning. For more
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information
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about a particular attribute, click on the link.</div>
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<br>
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<table border="1" cellpadding="2" cellspacing="2" width="100%">
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<caption><br>
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</caption><tbody>
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</tbody>
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<tbody>
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<tr>
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<td><b>Attribute Name</b></td>
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<td><b>Attribute Description</b></td>
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</tr>
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<tr>
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<td><a href="#ValidTimes">validTimes</a></td>
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<td>A list of start and end times for which the grids are
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valid.
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These are ordered start1, end1, start2, end2, etc. The time is in
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seconds from Jan 1, 1970 at 0000z.</td>
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</tr>
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<tr>
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<td><a href="#DescriptiveName">descriptiveName</a></td>
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<td>The descriptive name of the weather element.</td>
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</tr>
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<tr>
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<td><a href="#GridSize">gridsize</a></td>
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<td>The number of grid cells in each grid for this weather
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element
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(x, y)</td>
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</tr>
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<tr>
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<td><a href="#DomainOrigin">domainOrigin</a></td>
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<td>The lower left corner of the grid domain in AWIPS
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coordinates</td>
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</tr>
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<tr>
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<td><a href="#DomainExtent">domainExtent</a></td>
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<td>The extent of the domain in AWIPS coordinates</td>
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</tr>
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<tr>
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<td><a href="#MinMaxAllowedValues">minMaxAllowedValues</a></td>
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<td>The minimum and maximum values allowed, respectively
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for this
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weather element</td>
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</tr>
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<tr>
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<td><a href="#GridType">gridType</a></td>
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<td>The type of grid. The types are: SCALAR, VECTOR,
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WEATHER</td>
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</tr>
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<tr>
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<td><a href="#DatabaseID">databaseID</a></td>
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<td>Database identifier from which the grids were
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extracted.</td>
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</tr>
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<tr>
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<td><a href="#SiteID">siteID</a></td>
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<td>The site ID of the database from which the grids were
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extracted.</td>
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</tr>
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<tr>
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<td><a href="#Units">units</a></td>
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<td>The units of the values for these grids.</td>
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</tr>
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<tr>
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<td><a href="#Level">level</a></td>
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<td>The level of the data. For forecast data this is
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always
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"SFC"</td>
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</tr>
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<tr>
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<td><a href="#TimeConstraints">timeConstraints</a></td>
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<td>Three integers that represent the time constraints for
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the data.
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See GFE documentation for more details.</td>
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</tr>
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<tr>
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<td><a href="#Precision">precision</a></td>
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<td>Data precision for the gridded data. </td>
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</tr>
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<tr>
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<td><a href="#ProjectionInfo">projection info</a> (12
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items)</td>
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<td>All the infomation needed to reconstruct the
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projection on which
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this grid is defined.</td>
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</tr>
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<tr>
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<td>fillValue</td>
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<td>Data fill value which indicates that portions of the grid is
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not valid.</td>
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</tr>
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<tr>
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<td><a href="#dataMultiplier">dataMultiplier</a></td>
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<td>Data multiplier for the values contained in the grid.
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If not
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specified, defaults to 1.</td>
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</tr>
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<tr>
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<td><a href="#dataMultiplier">dataOffset</a></td>
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<td>Data offset for the values contained in the grid. If
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not specified,
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defaults to 0.</td>
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</tr>
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</tbody>
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</table>
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<br>
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<h3><a name="ValidTimes"></a>VaildTimes</h3>
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The valid times listed for a weather element define the start time and
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end time for each grid in terms of seconds since 01 Jan 1970.
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This
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is a
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standard format for representing time on UNIX systems. The times
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listed are organized in pairs. The first pair applies to the
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start
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time and
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end time of the first grid. The second pair applies to the start
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time and end time of the second grid, and so on. There should be
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exacty the
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same number of validTime pairs.
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<h3><a name="DescriptiveName"></a>Descriptive Name</h3>
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The descriptive name field provides a more detailed description of the
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parameter.
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<br>
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<h3><a name="GridSize"></a>GridSize</h3>
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The size of the grid in terms of grid cells expressed as a pair of
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numbers
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(x, y)
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<h3><a name="DomainOrigin"></a>DomainOrigin</h3>
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The (x, y) coordinate origin or lower-left corner of the grid domain in
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AWIPS coordinates. The AWIPS coordinates are expressed in terms
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of
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the
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current projection (usually the AWIPS 211 projection).
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<h3><a name="DomainExtent"></a>DomainExtent</h3>
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The (x, y) coordinate of the extent of the office domin expressed in
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the
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same coordinate system as the origin. This is always the offset
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from
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the
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origin. Adding this coordinate to the origin give the upper-right
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coordinate.
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<h3><a name="MinMaxAllowedValues"></a>MinMaxAllowedValues</h3>
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The minimum and maximum value allowed for this weather element
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expressed
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as a pair of numbers (min, max).
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<h3><a name="GridType"></a>GridType</h3>
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The data type for the grids. Possible values are SCALAR, VECTOR,
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and WEATHER.
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<h3><a name="DatabaseID"></a>DatabaseID</h3>
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The database identifier from which the grid originated. It has the
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format
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CCC_GRID__Fcst_YYYYMMDD_HHMM where,
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CCC is the site identifier, YYYY is the year, MM is the number of the
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month, DD is the day, HH is the hour and MM is the minute
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<h3><a name="SiteID"></a>SiteID</h3>
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The three letter identifier of the site from which the data originated.
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<h3><a name="Units"></a>Units</h3>
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The parameter units field indicates the units used by the data.
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<br>
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<h3><a name="Level"></a>Level</h3>
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The level for this weather element (e.g., 500MB). All surface
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data
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have the level SFC.
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<h3><a name="Precision"></a>Precision</h3>
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The number of significant decimal points for the data. A value of 0
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indicates
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that integer values are all that is important (even if there is more
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precision
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indicated by the data). A value of 1 indicates that the precision is 10
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-1 or 0.1.
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<h3><a name="TimeConstraints"></a>Time Constraints</h3>
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<div style="margin-bottom: 0in;">The time constraints consist of three
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elements: starting time, duration, and repeat interval. These values
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indicate
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the time limits that the parameter must obey. All grids for the
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parameter
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must be aligned on the specified time constraints. The starting time
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indicates
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the time of the first possible grid after 0000z. The duration indicates
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the length of the grid. The repeat interval defines how often the grid
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can repeat. All of the units are in seconds.
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For example, the illustration below
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shows
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the possible grid boundaries for a time constraint of starting time of
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0, duration of 6 hours, and repeat interval of 6 hours:</div>
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<div style="margin-bottom: 0in;"><img src="images/ifpAG-5.gif"
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name="Graphic3" border="0" height="118" width="487"></div>
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<div style="margin-bottom: 0in;">In the above example, grids can be a
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minimum of 6 hours long, but could be 12 or 18 or even 24 hours in
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length
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just as long as the starting and ending time of the grid falls on one
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of
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the defined above.
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A time constraint can be defined to have gaps in the data. For example,
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a 24-hour summary of daytime maximum temperature may have a constraint
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of starting time 900z, duration of 18 hours, and a repeat interval of
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24
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hours:
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<p><img src="images/ifpAG-6.gif" name="Graphic4" border="0" height="118"
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width="487"></p>
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<p>Most parameters are defined in the database with a one hour
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constraint
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(start time = 0000z, repeat = 1 hour, duration = 1h). Therefore the
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highest
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temporal resolution of the grids is one hour:
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</p>
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<p><img src="images/ifpAG-7.gif" name="Graphic5" border="0" height="118"
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width="487"></p>
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<p style="margin-bottom: 0in;">A special case exists which defines no
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constraints. This is the situation with a start time, repeat, and
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duration
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values all set to 0. The temporal resolution of the grids can be one
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second.</div>
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<br>
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<br>
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</p>
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<h3><a name="dataMultiplier"></a>Data Multiplier and Data Offset</h3>
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The data multiplier and data offset fields are only present when the -k
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krunch switch is provided to ifpnetCDF. This forces the data to
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be
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represented in few bits, if possible. The 32-bit floats may be
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converted
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to 16-bit or 8-bit integers. If converted, the netCDF attributes
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dataMultiplier and dataOffset will be available. The formula to
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convert
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the netCDF data values into real values is:
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<center>
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<p>data value = (netCDF value * dataMultiplier) + dataOffset</p>
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</center>
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<h3>
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<a name="ProjectionInfo"></a>Projection Info</h3>
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A series of values that allows one to
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precisely reconstruct the projection and thus remap the data to any
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other
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projection. These 12 values comprise all of the value required
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to reconstruct any valid AWIPS projection. Note that some are not
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used by all projection types. The attributes are latLonLL, latLonUR,
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gridPointLL,
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gridPointUR, projectionType, latLonOrigin, stdParallelOne,
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stdParallelTwo,
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lonOrigin, lonCenter.
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<br>
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<br>
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The grid represented in the netCDF file is usually smaller than the
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projection information indicates. The projection
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information, along with the <a href="#GridSize">Grid Size</a>, <a
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href="#DomainOrigin">Domain Origin</a>, and <a href="#DomainExtent">Domain
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Extent</a> information is used to define the location of the sub-grid
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on the Earth's surface.<br>
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<br>
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<br>
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<table nosave="" border="1" width="100%">
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<caption><br>
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</caption><tbody>
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</tbody>
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<tbody>
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<tr>
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<td><b>Attribute</b></td>
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<td><b>Used By</b></td>
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<td><b>Description</b></td>
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</tr>
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<tr nosave="">
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<td nosave="">latLonLL</td>
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<td>all projections</td>
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<td nosave="">specifies the latitude and longitude in degrees of
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the lower-left
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grid point in the projection. Note that it is defined as
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x=longitude,
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y=latitude so that the entry is (lon, lat).</td>
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</tr>
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<tr>
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<td>latLonUR</td>
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<td>all projections</td>
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<td>specifies the latitude and longitude in degrees of the
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lower-left grid
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point in the projection. Note that it is defined as x=longitude,
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y=latitude so that the entry is (lon, lat).</td>
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</tr>
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<tr>
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<td>gridPointLL</td>
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<td>all projections</td>
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<td>specifies the grid numbering system and the grid point number
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for the
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lower-left point in the projection. This is usually (1, 1)</td>
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</tr>
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<tr>
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<td>gridPointUR</td>
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<td>all projections</td>
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<td>specifies the grid numbering system and the grid point number
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for the
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upper-right most point in the projection. This is specified as
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(x,y).
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The projection grid size is gridPointUR-gridPointLL+1.</td>
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</tr>
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<tr>
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<td>projectionType</td>
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<td>all projections</td>
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<td>Projection types can be LAMBERT_CONFORMAL,
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POLAR_STEREOGRAPHIC, LATLON,
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or MERCATOR.</td>
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</tr>
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<tr>
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|
<td>latLonOrigin</td>
|
|
<td>LAMBERT_CONFORMAL only</td>
|
|
<td>Specified as (lon,lat). The longitude is the location
|
|
where the
|
|
projection has north as straight up. The latitude is typically
|
|
the
|
|
latitude intersect of the projection and earth which is the standard
|
|
parallel.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>stdParallelOne</td>
|
|
<td>LAMBERT_CONFORMAL only</td>
|
|
<td>Latitude intersect of projection and earth -- lower latitude.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>stdParallelTwo</td>
|
|
<td>LAMBERT_CONFORMAL only</td>
|
|
<td>Latitude intersect of projection and earth -- upper latitude.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>lonOrigin</td>
|
|
<td>POLAR_STEREOGRAPHIC only</td>
|
|
<td>Center longitude for the polar stereographic projection,
|
|
where the
|
|
projection has north as straight up.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>lonCenter</td>
|
|
<td>MERCATOR only</td>
|
|
<td>Center longitude for the mercator projection, where the
|
|
mercator projection
|
|
is parallel to the Earth's surface.</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<hr width="100%">
|
|
<h2><a name="History"></a>Grid Data History Format</h2>
|
|
The format of each Grid Data History entry consists of one or more
|
|
strings
|
|
separated by a caret (^). A grid can have more than one history
|
|
entry.
|
|
If only one exists, then there will not be a caret in the string.
|
|
Each string, a.k.a. history, consists of 7 or 8 tokens, separated
|
|
by a space. The table below describes each of these tokens in the
|
|
order in which they appear:
|
|
<br>
|
|
<table border="1" cellpadding="2" cellspacing="2" width="100%">
|
|
<caption><br>
|
|
</caption><tbody>
|
|
</tbody>
|
|
<tbody>
|
|
<tr>
|
|
<td valign="top">Token Number</td>
|
|
<td valign="top">Token</td>
|
|
<td valign="top">Description</td>
|
|
<td valign="top">Example</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">1</td>
|
|
<td valign="top">Grid Origin</td>
|
|
<td valign="top">Number describing the origin of the grid.
|
|
0=populated from
|
|
a model, 1=time interpolated, 2=created from scratch, 3=calculated, 4=
|
|
other.</td>
|
|
<td valign="top">0</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">2</td>
|
|
<td valign="top">Original Weather Element Identifier</td>
|
|
<td valign="top">String defining the original weather element
|
|
identifier
|
|
(ParmID) for this grid. This string is colon (:) and underscore (_)
|
|
separated
|
|
and always consists of several segments in this format:
|
|
parmName_level:siteID_GRID_optionalType_modelName_modelDate_modelTime</td>
|
|
<td valign="top">T_SFC:BOU_GRID_D2D_NAM_20020209_1200</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">3</td>
|
|
<td valign="top">Original Grid Starting Time</td>
|
|
<td valign="top">Original starting valid time of the grid in
|
|
seconds since
|
|
January 1, 1970 at 0000z..</td>
|
|
<td valign="top">1013472000</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">4</td>
|
|
<td valign="top">Original Grid Ending Time</td>
|
|
<td valign="top">Original ending valid time of the grid in
|
|
seconds since
|
|
January 1, 1970 at 0000z.</td>
|
|
<td valign="top">1913475600</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">5</td>
|
|
<td valign="top">Modification Time</td>
|
|
<td valign="top">Time when the grid was last modified by an edit
|
|
operation,
|
|
in seconds since January 1, 1970 at 0000z. If the grid has not
|
|
been
|
|
modified, this value is 0.</td>
|
|
<td valign="top">1913475900</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">6</td>
|
|
<td valign="top">Modification User</td>
|
|
<td valign="top">User that last modified the grid (WsId).
|
|
If the grid
|
|
has not been modified (token #5 is zero), then token #6 is not present
|
|
in the string, i.e., it is skipped. The format of this entry
|
|
is:
|
|
networkAddress:username:processName:pid:optLock. This describes the IP
|
|
address where the grid was modified, the user account, the name of the
|
|
process, the process identifier (PID), and an optional lock value.</td>
|
|
<td valign="top">2688174985:mark:gfe:19467:0</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">7</td>
|
|
<td valign="top">Update Time</td>
|
|
<td valign="top">Time when the grid was saved to GFE
|
|
(for local
|
|
grids), or time when the grid was created for Intersite Coordination
|
|
Grids
|
|
(ISC database). In seconds since January 1, 1970 at 0000z.
|
|
Note that grids from the published (Official) database reflect the time
|
|
the grid was first stored in the database, and not when it was
|
|
published. </td>
|
|
<td valign="top">1012791326</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">8</td>
|
|
<td valign="top">Publish Time</td>
|
|
<td valign="top">Time when the grid was published to the Official
|
|
database
|
|
in seconds since January 1, 1970 at 0000z. If this grid was not
|
|
published,
|
|
then this value will be 0.</td>
|
|
<td valign="top">0</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>
|
|
</p>
|
|
<hr size="2" width="100%">
|
|
<h3><a name="GlobalAttributes"></a>Global Attributes</h3>
|
|
The following table describes the global attributes contained in the
|
|
output
|
|
netCDF file:
|
|
<br>
|
|
|
|
<br>
|
|
<table border="1" cellpadding="2" cellspacing="2" width="100%">
|
|
<caption><br>
|
|
</caption><tbody>
|
|
</tbody>
|
|
<tbody>
|
|
<tr>
|
|
<td><b> Attribute Name</b></td>
|
|
<td> <b>Attribute Description</b></td>
|
|
</tr>
|
|
<tr>
|
|
<td> creationTime</td>
|
|
<td> An integer which represents the number of seconds
|
|
since January
|
|
1, 1970 at 0000z when this file was created.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>creationTimeString</td>
|
|
<td>A human-readable version of the creationTime</td>
|
|
</tr>
|
|
<tr>
|
|
<td>fileFormatVersion</td>
|
|
<td>A string, in the form of yyyymmdd, which represents the file
|
|
format
|
|
version.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>startProcTime</td>
|
|
<td>The value of the -s switch when this file is created, in the
|
|
form of
|
|
yyyymmdd. This and the endProcTime cover the total valid time of
|
|
the netCDF file. If the assumption is made that the netCDF file
|
|
contains
|
|
all grids over a particular time period, then the startProcTime and
|
|
endProcTime
|
|
cover that period. This is used to determine what times do NOT have
|
|
grids
|
|
available.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>endProcTime</td>
|
|
<td>The value of the -e switch when this file is created, in the
|
|
form of
|
|
yyyymmdd. This and the endProcTime cover the total valid time of
|
|
the netCDF file. If the assumption is made that the netCDF file
|
|
contains
|
|
all grids over a particular time period, then the startProcTime and
|
|
endProcTime
|
|
cover that period. This is used to determine what times do NOT have
|
|
grids
|
|
available.</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
</>
|
|
For purposes of formatting a netCDF file to be compatible with the <a
|
|
href="iscMosaic.html">iscMosaic</a>
|
|
program, the fileFormatVersion must be: 20010816 or 20030117.
|
|
<br>
|
|
<hr width="100%"><br>
|
|
<br>
|
|
<div class="Body">
|
|
<a href="GFESuite.html#TableOfContents">Back To TOC</a></div>
|
|
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|
|
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|