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<li class="toctree-l1 current"><a class="current reference internal" href="#">IDL interface</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#dimension-types">Dimension types</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#harp_import"><code class="docutils literal notranslate"><span class="pre">harp_import()</span></code></a></li>
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<section id="idl-interface">
<h1>IDL interface</h1>
<p>The Interactive Data Language (IDL) interface consists of a Dynamic Loadable
Module (DLM) that provides the <cite>harp_import</cite>, <cite>harp_export</cite>, <cite>harp_version</cite>,
and ‘harp_unload’ functions.</p>
<p>Products are represented in IDL as structures which can be manipulated freely
from within IDL. A product structure contains a field for each variable
contained in the product and contains the global attributes <cite>source_product</cite>
and <cite>history</cite> (if available). Each variable itself is again a structure containing
the variable attributes (<cite>unit</cite>, <cite>description</cite>, etc.) and a field <cite>data</cite> that
contains the data of the variable. The structure of a variable also contains a
field <cite>name</cite> that contains the case-sensitive name of the variable and (if the
variable is not a scalar) a field <cite>dimension</cite> that contains a list of dimension
names for each dimension of the variable.</p>
<p>Products can be exported as HARP compliant products in any of the file formats
supported by the HARP C library (netCDF/HDF4/HDF5). Such exported products can
subsequently be processed further using the <a class="reference internal" href="tools.html"><span class="doc">HARP command line tools</span></a>.</p>
<section id="dimension-types">
<h2>Dimension types</h2>
<p>Each non-scalar variable will have a <cite>dimension</cite> field in its structure, which
is a list of strings representing the dimension types (e.g. <cite>time</cite>, <cite>vertical</cite>,
<cite>latitude</cite>, etc.).</p>
</section>
<section id="data-types">
<h2>Data types</h2>
<p>The HARP IDL interface takes care of the conversion of product and variables
from the C domain to the IDL domain and back. This section describes the
relation between types in the C domain and types in the IDL domain.</p>
<p>The table below shows the type map that is used when importing or ingesting a
product, i.e. when translating from the C domain to the IDL domain.</p>
<p>Variable data arrays are converted to arrays in the product structure. The data
type used for the converted array is determined from the HARP data type of the
variable according to the type map shown below. Zero-dimensional arrays of
length 1 are converted to IDL scalars. The resulting IDL type is also shown in
the type map.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 64%" />
<col style="width: 36%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>HARP data type</p></th>
<th class="head"><p>IDL type</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>harp_type_int8</p></td>
<td><p>byte</p></td>
</tr>
<tr class="row-odd"><td><p>harp_type_int16</p></td>
<td><p>int</p></td>
</tr>
<tr class="row-even"><td><p>harp_type_int32</p></td>
<td><p>long</p></td>
</tr>
<tr class="row-odd"><td><p>harp_type_float</p></td>
<td><p>float</p></td>
</tr>
<tr class="row-even"><td><p>harp_type_double</p></td>
<td><p>double</p></td>
</tr>
<tr class="row-odd"><td><p>harp_type_string</p></td>
<td><p>string</p></td>
</tr>
</tbody>
</table>
<p>Note that the IDL <cite>byte</cite> type is an unsigned type (since IDL does not have any
8-bit signed type).
The HARP IDL interface will just hard cast signed int8 values to unsigned uint8
values (e.g. -1 will become 255). Make sure that in your operations within IDL
on these 8-bit integers you als treat them as mapped signed integers.
Note also that this holds for the <cite>valid_min</cite> and <cite>valid_max</cite> attributes
(e.g. <cite>valid_min</cite> may end up being higher than <cite>valid_max</cite> in IDL).</p>
</section>
<section id="unicode">
<h2>Unicode</h2>
<p>Zero-terminated C strings received from the HARP C library are always converted
to instances of type <code class="docutils literal notranslate"><span class="pre">string</span></code> in IDL which are unicode strings.</p>
</section>
<section id="examples">
<h2>Examples</h2>
<div class="highlight-IDL notranslate"><div class="highlight"><pre><span></span><span class="c1">; Import a file as a HARP product.</span><span class="w"></span>
prod<span class="w"> </span><span class="o">=</span><span class="w"> </span>harp_import(<span class="s2">"filename.ext"</span>)<span class="w"></span>
<span class="c1">; Print information about the product.</span><span class="w"></span>
<span class="nb">help</span>,<span class="w"> </span>prod,<span class="w"> </span><span class="o">/</span>struct<span class="w"></span>
<span class="c1">; Print information about the variable 'temperature'.</span><span class="w"></span>
<span class="nb">help</span>,<span class="w"> </span>prod.temperature,<span class="w"> </span><span class="o">/</span>struct<span class="w"></span>
<span class="c1">; Print the contents of the variable 'temperature'.</span><span class="w"></span>
<span class="nb">print</span>,<span class="w"> </span>prod.temperature.data<span class="w"></span>
<span class="c1">; Export the updated product as an HDF4 file (the format must be</span><span class="w"></span>
<span class="c1">; HDF4, HDF5 or netCDF, if no format is specified netCDF is used).</span><span class="w"></span>
result<span class="w"> </span><span class="o">=</span><span class="w"> </span>harp_export(prod,<span class="w"> </span><span class="s2">"filename.hdf"</span>,<span class="w"> </span><span class="s2">"hdf4"</span>)<span class="w"></span>
<span class="c1">; Print the result of the export.</span><span class="w"></span>
<span class="nb">print</span>,<span class="w"> </span>result<span class="w"></span>
<span class="c1">; Import the HDF4 file and perform an operation to exclude the variable</span><span class="w"></span>
<span class="c1">; temperature (variable name must be in uppercase).</span><span class="w"></span>
prod2<span class="w"> </span><span class="o">=</span><span class="w"> </span>harp_import(<span class="s2">"filename.hdf"</span>,<span class="w"> </span><span class="s2">"exclude(temperature)"</span>);<span class="w"></span>
<span class="c1">; Print information about the product.</span><span class="w"></span>
<span class="nb">help</span>,<span class="w"> </span>prod2,<span class="w"> </span><span class="o">/</span>struct<span class="w"></span>
</pre></div>
</div>
</section>
<section id="api-reference">
<h2>API reference</h2>
<p>This section describes the functions defined by the HARP IDL interface.</p>
<dl class="py function">
<dt class="sig sig-object py" id="harp_import">
<span class="sig-name descname"><span class="pre">harp_import</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">operations</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">''</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">options</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">''</span></span></em><span class="sig-paren">)</span></dt>
<dd><p>Import a product from a file.</p>
<p>This will first try to import the file as an HDF4, HDF5, or netCDF file that
complies to the HARP Data Format. If the file is not stored using the HARP
format then it will try to import it using one of the available ingestion
modules.</p>
<p>If the filename argument is a list of filenames or a globbing (glob.glob())
pattern then the harp.import_product() function will be called on each
individual file and the result of harp.concatenate() on the imported products
will be returned.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><ul class="simple">
<li><p><strong>filename</strong> (<em>str</em>) – Filename of the product to ingest</p></li>
<li><p><strong>operations</strong> (<em>str</em>) – Actions to apply as part of the import; should be
specified as a semi-colon separated string of operations.</p></li>
<li><p><strong>options</strong> (<em>str</em>) – Ingestion module specific options; should be specified as
a semi-colon separated string of key=value pairs; only
used if the file is not in HARP format.</p></li>
</ul>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><p>Ingested product or error structure.</p>
</dd>
</dl>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="harp_export">
<span class="sig-name descname"><span class="pre">harp_export</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">product</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">file_format</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'netcdf'</span></span></em><span class="sig-paren">)</span></dt>
<dd><p>Export a HARP compliant product.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><ul class="simple">
<li><p><strong>product</strong> (<em>str</em>) – Product to export.</p></li>
<li><p><strong>filename</strong> (<em>str</em>) – Filename of the exported product.</p></li>
<li><p><strong>file_format</strong> (<em>str</em>) – File format to use; one of ‘netcdf’, ‘hdf4’, or
‘hdf5’. If no format is specified, netcdf is used.</p></li>
</ul>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><p>Error structure with result code.</p>
</dd>
</dl>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="harp_version">
<span class="sig-name descname"><span class="pre">harp_version</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span></dt>
<dd><p>The harp_version function returns a string containing the current version
number of HARP. The version number is always of the format ‘x.y.z’, i.e.,
major, minor, and revision numbers, separated by dots.</p>
<dl class="field-list simple">
<dt class="field-odd">Returns</dt>
<dd class="field-odd"><p>HARP version number.</p>
</dd>
</dl>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="harp_unload">
<span class="sig-name descname"><span class="pre">harp_unload</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span></dt>
<dd><p>The harp_unload procedure will clean up any HARP resources. At the first
call to a HARP IDL function the HARP C Library will be initialized which
will require some memory.
A call to harp_unload can then be used to clean up these HARP resources.
After a clean up, the first call to a HARP IDL function will initialize
the HARP C Library again.</p>
<p>This function may be (slightly) useful on systems with little memory.</p>
</dd></dl>
</section>
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