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0001 <sect2 id="calc-geodetic">
0002 <title>Geodetic Coordinates module</title>
0003 <indexterm><primary>Tools</primary>
0004 <secondary>Astrocalculator</secondary>
0005 <tertiary>Geodetic Coordinates module</tertiary>
0006 </indexterm>
0008 <screenshot>
0009 <screeninfo>
0010 The Geodetic Coordinates calculator module
0011 </screeninfo>
0012 <mediaobject>
0013   <imageobject>
0014     <imagedata fileref="calc-geodetic.png" format="PNG"/>
0015   </imageobject>
0016   <textobject>
0017     <phrase>Geodetic Coordinates</phrase>
0018   </textobject>
0019 </mediaobject>
0020 </screenshot>
0022 <para>
0023 The normal <link linkend="ai-geocoords">geographic coordinate
0024 system</link> assumes that the Earth is a perfect sphere.  This is
0025 nearly true, so for most purposes geographic coordinates are fine.
0026 If very high precision is required, then we must take the true shape
0027 of the Earth into account.  The Earth is an ellipsoid; the distance
0028 around the equator is about 0.3% longer than a <link
0029 linkend="ai-greatcircle">Great Circle</link> that passes through the
0030 poles.  The <firstterm>Geodetic Coordinate system</firstterm> takes
0031 this ellipsoidal shape into account, and expresses the position
0032 on the Earth's surface in Cartesian coordinates (X, Y and Z) or in
0033 Geographic coordinates (Longitude, Latitude and Elevation).
0034 </para>
0036 <para>
0037 To use the module, first select which coordinates you will use as
0038 input in the <guilabel>Select Input Coordinates</guilabel> section: <guilabel>Cartesian</guilabel>
0039 or <guilabel>Geographic</guilabel> radio buttons.
0040 Then select an ellipsoid model and fill
0041 in the input coordinates in either the <guilabel>Cartesian
0042 Coordinates</guilabel> section or the <guilabel>Geographic
0043 Coordinates</guilabel> section.  When you press the
0044 <guibutton>Convert</guibutton> button, the corresponding
0045 coordinates will be filled in.
0046 </para>
0048 <para>
0049 The module contains a batch mode for converting several coordinate
0050 values at once.  You must construct an input file in which each line
0051 contains up to three numbers: the input coordinate values (either Cartesian
0052 or Geographic).  Then specify which coordinates you are using as input,
0053 and identify the input and output filenames.  Finally, press the
0054 <guibutton>Run</guibutton> button to generate the output file,
0055 which will contain the converted coordinates (Cartesian or
0056 Geographic; the complement of what you chose as the input values).
0057 </para>
0059 </sect2>