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<td></td>
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<h2>GRIB section 4, the binary data section</h2>
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An INTEGER array of at least 42 elements.
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<p>
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<table border="3">
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<caption>
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<strong>Contents of KSEC4</strong>
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</caption> <tbody>
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<tr>
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<th> Element </th>
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<th> Contents </th>
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<th> GRIB API keys<br>
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</th>
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</tr>
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<tr>
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<td> 1 </td>
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<td> Number of data values in array PSEC4 to be encoded or
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which have been decoded. When the 'A' coding option is used, the count
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is the number of image bytes stored four to an integer. When the 'B'
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coding option is used, the count is the number of integers used to
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return image bytes, stored four to an integer.
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<p> When a bitmap is used, this number includes the total
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of both missing and present data values. </p>
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<p> If this number is negative: </p>
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<li> the number of field points is -KSEC4(1), </li>
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<li> the entire field is missing, </li>
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<li> all values in PSEC4 are 0, </li>
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<li> the coded data has all the bits of its scale factor
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are set to 1 </li>
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<li> all the bits of the exponent and mantissa of its
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reference value are set to 1 (This is an ECMWF convention). </li>
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</td>
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<th style="vertical-align: top;"><div align="left">
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<p>numberOfPoints</p>
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<p>numberOfValues</p>
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<p>numberOfCodedValues</p>
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<p>numberOfMissing<br>
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</p>
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</div></th>
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</tr>
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<tr>
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<td> 2 </td>
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<td> Number of bits used for each encoded value. </td>
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<th style="vertical-align: top;"><div align="left">
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<p>decimalPrecision</p>
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<p>bitsPerValue</p>
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</div></th>
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</tr>
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<tr>
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<td> 3 </td>
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<td>
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<pre>Type of data:<br> 0 Grid point data.<br> 128 Spherical harmonic coefficients<br> (Used only if Section 2 is not included when <br> coding data.)</pre></td>
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<th style="vertical-align: top;"><div align="left"><a href="/publications/manuals/d/gribapi/keys/grids/">gridType</a><br>
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</div></th>
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</tr>
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<tr>
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<td> 4 </td>
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<td>
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<pre>Type of packing:<br> 0 Simple packing.<br> 64 Complex or second-order packing.<br></pre>
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</td>
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<th style="vertical-align: top;"><div align="left">packingType =<span class="style1">
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grid_simple | grid_ieee | spectral_complex | spectral_simple | <br>
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spectral_ieee | grid_simple_matrix | grid_second_order | <br>
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grid_second_order_different_width | grid_complex | <br>
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grid_complex_spatial_differencing | grid_jpeg | grid_png | <br>
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grid_simple_log_preprocessing<br>
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</span><br>
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</div></th>
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</tr>
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<tr>
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<td> 5 </td>
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<td>
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|
<pre>Data representation:<br> 0 Floating point data.<br> 32 Integer data.<br></pre>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 6 </td>
|
|
<td>
|
|
<pre>Additional flags indicator:<br> 0 No additional flags.<br> 16 Additional flags.<br></pre>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 7 </td>
|
|
<td> Reserved. Set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 8 </td>
|
|
<td>
|
|
<pre>Number of values indicator:<br> 0 Single datum at each grid point.<br> 64 Matrix of values at each grid point.<br></pre>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 9 </td>
|
|
<td>
|
|
<pre>Secondary bitmaps indicator:<br> 0 No secondary bitmaps.<br> 32 Secondary bitmaps present.<br></pre>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 10 </td>
|
|
<td>
|
|
<pre>Values width indicator:<br> 0 Second order values have constant width.<br> 16 Second order values have different widths.<br></pre>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 11 </td>
|
|
<td> Number of bits for second order values when these have
|
|
constant width. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 12-15 </td>
|
|
<td> Reserved for WMO reserved flag fields. Set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 16 </td>
|
|
<td> For complex packing, a pointer to the start of packed
|
|
data values (ie the octet number). Otherwise set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 17 </td>
|
|
<td> For complex packing, the scaling factor P, stored as
|
|
the INTEGER value P*1000 (in the range -10000 to +10000). Otherwise set
|
|
to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 18 </td>
|
|
<td> For complex packing, the pentagonal resolution
|
|
parameter J specifying the truncation of the subset of the data
|
|
represented as 32-bit floating point numbers (ie not packed). Otherwise
|
|
set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 19 </td>
|
|
<td> For complex packing, the pentagonal resolution
|
|
parameter K specifying the truncation of the subset of the data
|
|
represented as 32-bit floating point numbers (ie not packed). Otherwise
|
|
set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 20 </td>
|
|
<td> For complex packing, the pentagonal resolution
|
|
parameter M specifying the truncation of the subset of the data
|
|
represented as 32-bit floating point numbers (ie not packed). Otherwise
|
|
set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 21 </td>
|
|
<td> The number of non-missing values in a field which uses
|
|
a bitmap.
|
|
<p>When the 'B' coding option is used, this count is the
|
|
number of image bytes
|
|
(versions of GRIBEX after 13.040). </p>
|
|
</td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 22-33 </td>
|
|
<td> Reserved. Set to 0. </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
<tr>
|
|
<td> 34 </td>
|
|
<td> An offset bit pointer to coded values in the GRIB
|
|
record. (This is returned by the 'G', 'I' or 'J' decoding options). </td>
|
|
<th style="vertical-align: top;"><div align="left"><br>
|
|
</div></th>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
</p>
|
|
<h2>X decoding option.</h2>
|
|
Elements 34 to 42 are used only for the 'X' option, which decodes up to
|
|
4 values. (See HOPER above). The scanning mode must be from West to
|
|
East and from North to South.
|
|
<table border="3">
|
|
<caption><strong> KSEC4 - X decoding option </strong></caption><tbody>
|
|
<tr>
|
|
<th> Element </th>
|
|
<th> Contents </th>
|
|
</tr>
|
|
<tr>
|
|
<td> 34 </td>
|
|
<td> Number of points to be decoded (maximum 4). </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 35 </td>
|
|
<td> Number of the latitude row of the first value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 36 </td>
|
|
<td> Number of the longitude point of the first value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 37 </td>
|
|
<td> Number of the latitude row of the second value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 38 </td>
|
|
<td> Number of the longitude point of the second value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 39 </td>
|
|
<td> Number of the latitude row of the third value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 40 </td>
|
|
<td> Number of the longitude point of the third value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 41 </td>
|
|
<td> Number of the latitude row of the fourth value. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 42 </td>
|
|
<td> Number of the longitude point of the fourth value. </td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<h2>Grid point matrix packing.</h2>
|
|
For grid point packing, with a matrix of values at each grid point,
|
|
elements 50 to (50+NC1+NC2) are used as follows:
|
|
<table border="3">
|
|
<caption><strong> KSEC4 - grid matrix packing </strong></caption><tbody>
|
|
<tr>
|
|
<th> Element </th>
|
|
<th> Contents </th>
|
|
</tr>
|
|
<tr>
|
|
<td> 50 </td>
|
|
<td> First dimension of each matrix (the number of rows). </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 51 </td>
|
|
<td> Second dimension of each matrix (the number of
|
|
columns). </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 52 </td>
|
|
<td> First dimension coordinate values definition. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 53 </td>
|
|
<td> Number of coefficients or values used to specify the
|
|
first dimension coordinate function, NC1. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 54 </td>
|
|
<td> Second dimension coordinate values definition. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 55 </td>
|
|
<td> Number of coefficients or values used to specify the
|
|
second dimension coordinate function, NC2. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 56 </td>
|
|
<td> First dimension physical significance. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 57 </td>
|
|
<td> Second dimension physical significanc. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> 58 - 59 </td>
|
|
<td> Reserved. Set to 0. </td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<h2>ECMWF use of REALs.</h2>
|
|
In the WMO specification, the following fields are INTEGER values.
|
|
ECMWF uses floating-point values for its wave models, so these fields
|
|
contain REAL values in both input and output.
|
|
<table border="3">
|
|
<caption><strong> KSEC4 - ECMWF use of REALs </strong></caption><tbody>
|
|
<tr>
|
|
<th> Elements </th>
|
|
<th> Contents </th>
|
|
</tr>
|
|
<tr>
|
|
<td> 60 - (59+NC1) </td>
|
|
<td> Coefficients to define the first dimension coordinate
|
|
values in functional form, or the explicit coordinate values. </td>
|
|
</tr>
|
|
<tr>
|
|
<td> (60+NC1)-(59+NC1+NC2) </td>
|
|
<td> Coefficients to define the second dimension coordinate
|
|
values in functional form, or the explicit coordinate values </td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
|
|
|
|
|
|
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