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">
<Placemark>
<name>Simple placemark</name>
<description>Attached to the ground. Intelligently places itself
at the height of the underlying terrain.
</description>
<Point>
<coordinates>-122.0822035425683,37.42228990140251,0</coordinates>
</Point>
</Placemark>
</kml>
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">
（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>，<Snippet>和<BalloonStyle>中的<text>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>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">
<Document>
<Placemark>
<name>CDATA example</name>
<description>
<![CDATA[
<h1>CDATA Tags are useful!</h1>
<p><font color="red">Text is <i>more readable</i> and
<b>easier to write</b> when you can avoid using entity
references.</font></p>
]]>
</description>
<Point>
<coordinates>102.595626,14.996729</coordinates>
</Point>
</Placemark>
</Document>
</kml>
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">
<Document>
<Placemark>
<name>Entity references example</name>
<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>
</description>
<Point>
<coordinates>102.594411,14.998518</coordinates>
</Point>
</Placemark>
</Document>
</kml>
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">
<Folder>
<name>Ground Overlays</name>
<description>Examples of ground overlays</description>
<GroundOverlay>
<name>Large-scale overlay on terrain</name>
<description>Overlay shows
<Icon>
<href>http://code.google.com/apis/kml/documentation/etna.jpg</href>
</Icon>
<LatLonBox>
<north>37.91904192681665</north>
<south>37.46543388598137</south>
<east>15.35832653742206</east>
<west>14.60128369746704</west>
<rotation>-0.1556640799496235</rotation>
</LatLonBox>
</GroundOverlay>
</Folder>
</kml>
在<GroundOverlay>中，它包含两个较新的标记：
<Icon>：指定图片的URL；
<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>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">
<Document>
<name>Paths</name>
<description>Examples of paths. Note that the tessellate tag is by default set to 0. If you want to create tessellated lines, they must be authored (or edited) directly in KML.</description>
<Style id="yellowLineGreenPoly">
<LineStyle>
<color>7f00ffff</color>
<width>4</width>
</LineStyle>
<PolyStyle>
<color>7f00ff00</color>
</PolyStyle>
</Style>
<Placemark>
<name>Absolute Extruded</name>
<description>Transparent green wall with yellow outlines</description> <styleUrl>#yellowLineGreenPoly</styleUrl>
<LineString>
<extrude>1</extrude>
<tessellate>1</tessellate>
<altitudeMode>absolute</altitudeMode>
<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
</coordinates>
</LineString>
</Placemark>
</Document>
</kml>
1.5 多边形
多边形由<Polygon>定义，包括<outerBoundaryIs>和<innerBoundaryIs>，如下所示：
<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://earth.google.com/kml/2.1">
<Placemark>
<name>The Pentagon</name>
<Polygon>
<extrude>1</extrude>
<altitudeMode>relativeToGround</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<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
</coordinates>
</LinearRing>
</outerBoundaryIs>
<innerBoundaryIs>
<LinearRing>
<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
</coordinates>
</LinearRing>
</innerBoundaryIs>
</Polygon>
</Placemark>
</kml>
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