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 <span id="projectnumber">1.49</span>
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<div class="title">Introduction </div> </div>
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<div class="textblock"><center> Forward to <a class="el" href="install.html">Installing GeographicLib</a>. Up to <a class="el" href="index.html#contents">Contents</a>. </center><p><a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a> offers a C++ interfaces to a small (but important!) set of geographic transformations. It grew out of a desire to improve on the <a href="http://earth-info.nga.mil/GandG/geotrans/">geotrans</a> package for transforming between geographic and <a class="el" href="classGeographicLib_1_1MGRS.html" title="Convert between UTM/UPS and MGRS. ">MGRS</a> coordinates. At present, <a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a> provides UTM, UPS, <a class="el" href="classGeographicLib_1_1MGRS.html" title="Convert between UTM/UPS and MGRS. ">MGRS</a>, geocentric, and local cartesian projections, gravity and geomagnetic models, and classes for geodesic calculations.</p>
<p>The goals of <a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a> are:</p><ul>
<li>Accuracy. In most applications the accuracy is close to round-off, about 5 nm (5 nanometers). Even though in many geographic applications 1 cm is considered "accurate enough", there is little penalty in providing much better accuracy. In situations where a faster approximate algorithm is necessary, <a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a> offers an accurate benchmark to guide the development.</li>
<li>Completeness. For each of the projections included, an attempt is made to provide a complete solution. For example, <a class="el" href="classGeographicLib_1_1Geodesic.html#afdca5eb7c37fa2fecf124aecd6c436fd">Geodesic::Inverse</a> works for anti-podal points. Similarly, <a class="el" href="classGeographicLib_1_1Geocentric.html#a14fde4d04f816f2d1f433590865cf16f">Geocentric.Reverse</a> will return accurate geodetic coordinates even for points close to the center of the earth.</li>
<li>C++ interface. For the projection methods, this allows encapsulation of the ellipsoid parameters.</li>
<li>Emphasis on projections necessary for analyzing military data.</li>
<li>Uniform treatment of UTM/UPS. The <a class="el" href="classGeographicLib_1_1UTMUPS.html" title="Convert between geographic coordinates and UTM/UPS. ">UTMUPS</a> class treats UPS as zone 0. This simplifies conversions between UTM and UPS coordinates, etc.</li>
<li>Well defined and stable conventions for the conversion between UTM/UPS to <a class="el" href="classGeographicLib_1_1MGRS.html" title="Convert between UTM/UPS and MGRS. ">MGRS</a> coordinates.</li>
<li>Detailed internal documentation on the algorithms. For the most part <a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a> uses published algorithms and references are given. If changes have been made (usually to improve the numerical accuracy), these are described in the code.</li>
</ul>
<p>Various <a class="el" href="utilities.html">Utility programs</a> are provided with the library. These illustrate the use of the library and are useful in their own right. This library and the utilities have been tested with g++ 5.3.1 under Linux, with Apple LLVM 7.0.2 under Mac OS X, and with MS Visual Studio 10 (2010), 11 (2012), 12 (2013), 14 (2015), and 15 (2017) compiled for 32 bit and 64 bit on Windows.</p>
<p>MATLAB, JavaScript, and Python interfaces are provided to portions of <a class="el" href="namespaceGeographicLib.html" title="Namespace for GeographicLib. ">GeographicLib</a>; see <a class="el" href="other.html">Implementations in other languages</a>.</p>
<p>The section <a class="el" href="geodesic.html">Geodesics on an ellipsoid of revolution</a> documents the method of solving the geodesic problem.</p>
<p>The section <a class="el" href="transversemercator.html">Transverse Mercator projection</a> documents various properties of this projection.</p>
<p>The bulk of the testing has used geographically relevant values of the flattening. Thus, you can expect close to full accuracy for −0.01 ≤ <em>f</em> ≤ 0.01 (but note that <a class="el" href="classGeographicLib_1_1TransverseMercatorExact.html" title="An exact implementation of the transverse Mercator projection. ">TransverseMercatorExact</a> is restricted to <em>f</em> > 0). However, reasonably accurate results can be expected if −0.1 ≤ <em>f</em> ≤ 0.1. Outside this range, you should attempt to verify the accuracy of the routines independently. Two types of problems may occur with larger values of <em>f</em>:</p><ul>
<li>Some classes, specifically <a class="el" href="classGeographicLib_1_1Geodesic.html" title="Geodesic calculations ">Geodesic</a>, <a class="el" href="classGeographicLib_1_1GeodesicLine.html" title="A geodesic line. ">GeodesicLine</a>, and <a class="el" href="classGeographicLib_1_1TransverseMercator.html" title="Transverse Mercator projection. ">TransverseMercator</a>, use series expansions using <em>f</em> as a small parameter. The accuracy of these routines will degrade as <em>f</em> becomes large.</li>
<li>Even when exact formulas are used, many of the classes need to invert the exact formulas (e.g., to invert a projection), typically, using Newton's method. This usually provides an essentially exact inversion. However, the choice of starting guess and the exit conditions have been tuned to cover small values of <em>f</em> and the inversion may be incorrect if <em>f</em> is large.</li>
</ul>
<p>Undoubtedly, bugs lurk in this code and in the documentation. Please report any you find to <a href="#" onclick="location.href='mai'+'lto:'+'cha'+'rl'+'es@'+'ka'+'rne'+'y.'+'com'; return false;">charl<span style="display: none;">.nosp@m.</span>es@k<span style="display: none;">.nosp@m.</span>arney<span style="display: none;">.nosp@m.</span>.com</a>.</p>
<center> Forward to <a class="el" href="install.html">Installing GeographicLib</a>. Up to <a class="el" href="index.html#contents">Contents</a>. </center> </div></div><!-- contents -->
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