GOOGLE地球浏览器分析（五）：KML文件基本格式

GOOGLE地球浏览器分析（五）：KML文件基本格式

粟卫民http://www.gisdev.cn/ http://blog.csdn.net/suen/ 日期：<chsdate year="2007" month="7" day="5" islunardate="False" isrocdate="False" w:st="on"><span lang="EN-US">2007-7-5</span></chsdate>

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第三节我们介绍了KML文件的定义及其在GOOGLE地图浏览器中的地位，并给出了一个简单的样例文件。下面我们详细介绍KML文件的格式。

1 基本格式

基本格式的KML文件是指可以直接由Google Earth创建的KML文件，它包括地点标记、叠层、路线和多边形。下面分别介绍。

1.1 地点标记（Placemarks）

上一节我们给出了一个地点标记（Placemarks）的示例。地点标记是Google Earth中最常用的地理特征，它使用一个黄色的图钉在地球表面标记一个位置。一个简单的地点标记的KML代码如下所示：

<?xml version="1.0" encoding="UTF-8"?>

<kml xmlns="http://earth.google.com/kml/2.1"></kml>

<placemark><span style=""> </span></placemark>

<name>Simple placemark</name>

<description>Attached to the ground. Intelligently places itself </description>

at the height of the underlying terrain.

<point><span style=""> </span></point>

<coordinates>-122.0822035425683,37.42228990140251,0</coordinates>

它包括以下几个部分：

（1）XML头：<?xml version="1.0" encoding="UTF-8"?>

（2）KML命名空间定义：<kml xmlns="http://earth.google.com/kml/2.1"></kml>

（3）地点标记对象，包括：

名称（name）：用于对地点标记进行注记；

描述（description）：对地点标记进行描述，“气球（ballon）”中的显示内容；

点（Point）：指定地点标记的位置。

1.2 使用HTML描述地点标记

有两种方式来使用HTML描述地点标记，一种是直接在<description></description>，<snippet></snippet>和<balloonstyle></balloonstyle>中的标记中写入标准HTTP超链接地址，如www.google.com，这样Google Earth 4.0及更高版本将利用Auto-Markup技术自动把它显示为超链接。另一种是使用CDATA元素在<description></description>标记中写入自己的HTML标记语言，如下所示：

<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1"></kml>

<document></document>

<placemark></placemark>

<name>CDATA example</name>

<description></description>

CDATA Tags are useful!

Text is more readable and

easier to write when you can avoid using entity

references.

]]>

<point></point>

<coordinates>102.595626,14.996729</coordinates>

当然，还有一种使用转义字符来表示特殊符号的方式，这就不需要CDATA元素，如下所示：

<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1"></kml>

<document></document>

<placemark></placemark>

<name>Entity references example</name>

<description></description>

<h1>Entity references are hard to type!</h1>

<p><font color="green">Text is

<i>more readable</i>

and <b>easier to write</b>

when you can avoid using entity references.</font></p>

<point></point>

<coordinates>102.594411,14.998518</coordinates>

1.3叠层

叠层是覆盖在地球表面的图像。一个简单的叠层KML代码如下所示：

<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1"></kml>

<folder><span style=""> </span></folder>

<name>Ground Overlays</name>

<description>Examples of ground overlays</description>

<groundoverlay><span style=""> </span></groundoverlay>

<name>Large-scale overlay on terrain</name>

<description>Overlay shows <place w:st="on">Mount Etna</place> erupting on July 13th, 2001.</description>

<icon><span style=""> </span></icon>

<href>http://code.google.com/apis/kml/documentation/etna.jpg</href>

<latlonbox><span style=""> </span></latlonbox>

<north>37.91904192681665</north>

<south>37.46543388598137</south>

<east>15.35832653742206</east>

<west>14.60128369746704</west>

<rotation>-0.1556640799496235</rotation>

在<groundoverlay></groundoverlay>中，它包含两个较新的标记：

<icon></icon>：指定图片的URL；

<latlonbox></latlonbox>：指定图片的位置和范围。

Google Earth支持JPEG，BMP， GIF， TIFF， TGA和PNG等格式的图像。

1.4 路线

在KML里面，路线由<linestring></linestring>元素来创建。如下所示：

<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1"></kml>

<document><span style=""> </span></document>

<name>Paths</name>

<description>Examples of paths. Note that the tessellate tag is by default<span style=""> </span>set to 0. If you want to create tessellated lines, they must be authored<span style=""> </span>(or edited) directly in KML.</description>

<style id="yellowLineGreenPoly"><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"><LineStyle><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"><color>7f00ffff</color><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"><width>4</width><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"></LineStyle><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"><PolyStyle><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"><color>7f00ff00</color><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"></PolyStyle><span style=""> </span></span></p><p class="MsoNormal"><span lang="EN-US"></style>

<placemark></placemark>

<name>Absolute Extruded</name>

<description>Transparent green wall with yellow outlines</description> <styleurl>#yellowLineGreenPoly</styleurl>

<linestring><span style=""> </span></linestring>

<extrude>1</extrude>

<tessellate>1</tessellate>

<altitudemode>absolute</altitudemode>

<coordinates></coordinates>

-112.2550785337791,36.07954952145647,2357 -112.2549277039738,36.08117083492122,2357 -112.2552505069063,36.08260761307279,2357 -112.2564540158376,36.08395660588506,2357 -112.2580238976449,36.08511401044813,2357 -112.2595218489022,36.08584355239394,2357 -112.2608216347552,36.08612634548589,2357 -112.262073428656,36.08626019085147,2357 -112.2633204928495,36.08621519860091,2357 -112.2644963846444,36.08627897945274,2357 -112.2656969554589,36.08649599090644,2357

1.5 多边形

多边形由定义，包括<outerboundaryis></outerboundaryis>和<innerboundaryis></innerboundaryis>，如下所示：

<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1"></kml>

<placemark><span style=""> </span></placemark>

<name>The Pentagon</name>

<extrude>1</extrude>

<altitudemode>relativeToGround</altitudemode>

<outerboundaryis><span style=""> </span></outerboundaryis>

<linearring><span style=""> </span></linearring>

<coordinates><span style=""> </span></coordinates>

-77.05788457660967,38.87253259892824,100 -77.05465973756702,38.87291016281703,100 -77.05315536854791,38.87053267794386,100 -77.05552622493516,38.868757801256,100 -77.05844056290393,38.86996206506943,100 -77.05788457660967,38.87253259892824,100

<innerboundaryis><span style=""></span></innerboundaryis>

<linearring><span style=""> </span></linearring>

<coordinates><span style=""> </span></coordinates>

-77.05668055019126,38.87154239798456,100 -77.05542625960818,38.87167890344077,100 -77.05485125901024,38.87076535397792,100 -77.05577677433152,38.87008686581446,100 -77.05691162017543,38.87054446963351,100 -77.05668055019126,38.87154239798456,100

注：本文大部分内容是由GOOGLE KML文档KML Samples翻译而来，如果GOOGLE公司觉得有什么不妥，请联系我修改或删除。

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