[分享] 地理坐标系与投影坐标系的区别

  
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">首先理解地理坐标系（<span lang="EN-US">Geographic coordinate system</span>），直译为 <b style="mso-bidi-font-weight: normal">地理坐标系统</b>，是以经纬度为地图的存储单位的。很明显，<span lang="EN-US">Geographic coordinate system</span>是球面坐标系统。<span lang="EN-US"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">我们要将地球上的数字化信息存放到球面坐标系统上，如何进行操作呢？地球是一个不规则的椭球，如何将数据信息以科学的方法存放到椭球上？<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">这必然要求我们找到这样的一个椭球体。这样的椭球体具有特点：可以量化计算的。具有长半轴，短半轴，偏心率。以下几行便是<span lang="EN-US">Krasovsky_1940</span>椭球及其相应参数。<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US">Spheroid: Krasovsky_1940 <br/>Semimajor Axis: 6378245.000000000000000000 <br/>Semiminor Axis: 6356863.018773047300000000 <br/>Inverse Flattening</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">（扁率）<span lang="EN-US">: 298.300000000000010000 <br/></span>然而有了这个椭球体以后还不够，还需要一个大地基准面将这个椭球定位。在坐标系统描述中，可以看到有这么一行：<span lang="EN-US"> <br/>Datum: D_Beijing_1954 <br/></span>表示，大地基准面是<span lang="EN-US">D_Beijing_1954</span>。<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">有了<span lang="EN-US">Spheroid</span>和<span lang="EN-US">Datum</span>两个基本条件，地理坐标系统便可以使用。<span lang="EN-US"> <br/></span>完整参数：<span lang="EN-US"> <br/>Alias: <br/>Abbreviation: <br/>Remarks: <br/>Angular Unit: Degree (0.017453292519943299) <br/>Prime Meridian</span>（起始经度）<span lang="EN-US">: Greenwich (0.000000000000000000) <br/>Datum</span>（大地基准面）<span lang="EN-US">: D_Beijing_1954 <br/>Spheroid</span>（参考椭球体）<span lang="EN-US">: Krasovsky_1940 <br/>Semimajor Axis: 6378245.000000000000000000 <br/>Semiminor Axis: 6356863.018773047300000000 <br/>Inverse Flattening: 298.300000000000010000<o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">接下来便是<span lang="EN-US">Projection coordinate system</span>（<b style="mso-bidi-font-weight: normal">投影坐标系统</b>），首先看看投影坐标系统中的一些参数。<span lang="EN-US"> <br/>Projection: Gauss_Kruger <br/>Parameters: <br/>False_Easting: 500000.000000 <br/>False_Northing: 0.000000 <br/>Central_Meridian: 117.000000 <br/>Scale_Factor: 1.000000 <br/>Latitude_Of_Origin: 0.000000<o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US">Linear Unit: Meter (1.000000) <br/>Geographic Coordinate System: <br/>Name: GCS_Beijing_1954 <br/>Alias: <br/>Abbreviation: <br/>Remarks: <br/>Angular Unit: Degree (0.017453292519943299) <br/>Prime Meridian: Greenwich (0.000000000000000000) <br/>Datum: D_Beijing_1954 <br/>Spheroid: Krasovsky_1940 <br/>Semimajor Axis: 6378245.000000000000000000 <br/>Semiminor Axis: 6356863.018773047300000000 <br/>Inverse Flattening: 298.300000000000010000 <br/></span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">从参数中可以看出，每一个投影坐标系统都必定会有<span lang="EN-US">Geographic Coordinate System</span>。<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b style="mso-bidi-font-weight: normal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">投影坐标系统</span></b><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">，实质上便是平面坐标系统，其地图单位通常为米。<span lang="EN-US"> <br/></span>那么为什么投影坐标系统中要存在坐标系统的参数呢？ <span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><br/></span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">这时候，又要说明一下投影的意义：<span style="COLOR: red">将球面坐标转化为平面坐标的过程便称为投影</span>。<span lang="EN-US"> <br/></span>好了，投影的条件就出来了：<span lang="EN-US"> <br/>a</span>、球面坐标<span lang="EN-US"> <br/>b</span>、转化过程（也就是算法）<span lang="EN-US"> <br/></span>也就是说，要得到投影坐标就必须得有一个<span lang="EN-US">“</span>拿来<span lang="EN-US">”</span>投影的球面坐标，然后才能使用算法去投影！<span lang="EN-US"> <br/></span>即每一个投影坐标系统都必须要求有<span lang="EN-US">Geographic Coordinate System</span>参数。<span lang="EN-US"> <br style="mso-special-character: line-break"/><br style="mso-special-character: line-break"/><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">我们现在看到的很多教材上的对坐标系统的称呼很多，都可以归结为上述两种投影。其中包括我们常见的<span lang="EN-US">“</span>非地球投影坐标系统<span lang="EN-US">”</span>。<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>

  
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">另， <b style="mso-bidi-font-weight: normal">大地坐标（<span lang="EN-US">Geodetic Coordinate</span>）</b><span lang="EN-US">:</span>大地测量中以参考椭球面为基准面的坐标。地面点<span lang="EN-US">P</span>的位置用大地经度<span lang="EN-US">L</span>、大地纬度<span lang="EN-US">B</span>和大地高<span lang="EN-US">H</span>表示。当点在参考椭球面上时，仅用大地经度和大地纬度表示。大地经度是通过该点的大地子午面与起始大地子午面之间的夹角，大地纬度是通过该点的法线与赤道面的夹角，大地高是地面点沿法线到参考椭球面的距离。<span lang="EN-US"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><span style="mso-spacerun: yes"> </span><br/></span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">方里网<span lang="EN-US">:</span>是由平行于投影坐标轴的两组平行线所构成的方格网。因为是每隔整公里绘出坐标纵线和坐标横线，所以称之为方里网，由于方里线同时 又是平行于直角坐标轴的坐标网线，故又称直角坐标网。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><br/></span><span style="FONT-FAMILY: 宋体; COLOR: red; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">在<span lang="EN-US">1</span>：<span lang="EN-US">1</span>万<span lang="EN-US">——1</span>：<span lang="EN-US">20</span>万比例尺的地形图上，经纬线只以图廓线的形式直接表现出来，并在图角处注出相应度数。为了在用图时加密成网，在内外图廓间还绘有加密经纬网的加密分划短线<span lang="EN-US">(</span>图式中称<span lang="EN-US">“</span>分度带<span lang="EN-US">”)</span>，必要时对应短线相连就可以构成加密的经纬线网。<span lang="EN-US">1</span>：<span lang="EN-US">2 5</span>万地形图上，除内图廓上绘有经纬网的加密分划外，图内还有加密用的十字线。</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt"> <span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><br/></span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">我国的<span lang="EN-US">1</span>：<span lang="EN-US">50</span>万<span lang="EN-US">——1</span>：<span lang="EN-US">100</span>万地形图，在图面上直接绘出经纬线网，内图廓上也有供加密经纬线网的加密分划短线。 <span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><br/></span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">直角坐标网的坐标系以中央经线投影后的直线为<span lang="EN-US">X</span>轴，以赤道投影后的直线为<span lang="EN-US">Y</span>轴，它们的交点为坐标原点。这样，坐标系中就出现了四 个象限。纵坐标从赤道算起向北为正、向南为负；横坐标从中央经线算起，向东为正、向西为负。<span lang="EN-US"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt">虽然我们可以认为方里网是直角坐标，大地坐标就是球面坐标。但是我们在一副地形图上经常见到方里网和经纬度网，我们很习惯的称经纬度网为大地坐标，这个时候的大地坐标不是球面坐标，她与方里网的投影是一样的（一般为高斯），也是平面坐标。<span lang="EN-US"><o:p></o:p></span></span></p>

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