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44 lines
1.6 KiB
44 lines
1.6 KiB
<sect2 id="calc-geodetic">
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<title>Geodetic Coordinates module</title>
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<indexterm><primary>Tools</primary>
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<secondary>Astrocalculator</secondary>
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<tertiary>Geodetic Coordinates module</tertiary>
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</indexterm>
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<screenshot>
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<screeninfo>
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The Geodetic Coordinates calculator module
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</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="calc-geodetic.png" format="PNG"/>
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</imageobject>
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<textobject>
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<phrase>Geodetic Coordinates</phrase>
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</textobject>
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</mediaobject>
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</screenshot>
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<para>
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The normal <link linkend="ai-geocoords">geographic coordinate
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system</link> assumes that the Earth is a perfect sphere. This is
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nearly true, so for most purposes geographic coordinates are fine.
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If very high precision is required, then we must take the true shape
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of the Earth into account. The Earth is an ellipsoid; the distance
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around the equator is about 0.3% longer than a <link
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linkend="ai-greatcircle">Great Circle</link> that passes through the
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poles. The <firstterm>Geodetic Coordinate system</firstterm> takes
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this ellipsoidal shape into account, and expresses the position
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on the Earth's surface in Cartesian coordinates (X, Y, and Z).
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</para>
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<para>
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To use the module, first select which coordinates you will use as
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input in the <guilabel>Input Selection</guilabel> section. Then, fill
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in the input coordinates in either the <guilabel>Cartesian
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Coordinates</guilabel> section or the <guilabel>Geographic
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Coordinates</guilabel> section. When you press the
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<guibutton>Compute</guibutton> button, the corresponding
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coordinates will be filled in.
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</para>
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</sect2>
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