Google Earth与Python CGI交互例子

看了Servlet-based Google Earth Tours感觉挺好，不过他这个不够简单，我来仿照KML官方网站的python例子，写个简单的小例子把文章的精髓拿出来.

快速体验：

1. 把下面的getest.kml和getest.py保存到本机。

2.把getest.py的第一行改成你的python解释器路径，并放到Apache的cgi-bin下。

3. 双击getest.kml会启动google earth，在Place面板里会出现Python Demo目录，选中它，当你移动屏幕的时候，你会发现屏幕中心一直会有一个placemark，这个placemark是python程序动态返回的。



原理介绍：

1. 先看看KML的<NetworkLink>标签的样子，比如getest.kml


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


<kml xmlns="http://earth.google.com/kml/2.2">


<Folder>


<name>Python Demo</name>


<visibility>0</visibility>


<open>0</open>


<description>Liu Test</description>




<NetworkLink>


<name>Random Placemark</name>


<visibility>0</visibility>


<open>0</open>


<description>my discription</description>


<refreshVisibility>0</refreshVisibility>


<flyToView>0</flyToView>


<Link>


<href>http://localhost/cgi-bin/getest.py</href>


<refreshInterval>2</refreshInterval>


<viewRefreshMode>onStop</viewRefreshMode>


<viewRefreshTime>1</viewRefreshTime>


</Link>


</NetworkLink>




</Folder>


</kml>



这里主要有两个地方：

一个是 <href>http://localhost/cgi-bin/getest.py</href> ，GE向这个URL要数据，并把BBOX以GET方式发送到该URL，比如http://localhost/cgi-bin/getest.py?bbox=121,36,122,37

另一个是<refreshInterval>2</refreshInterval>


<viewRefreshMode>onStop</viewRefreshMode>


<viewRefreshTime>1</viewRefreshTime>

这几个标签指定了GE发送数据的时间间隔和其他设定。

当我们在GE中打开这个KML文件的时候，GE就回向 http://localhost/cgi-bin/getest.py 要数据，我们就可以在getest.py中对该请求进行处理，并返回结果(KML)。

2. 第二步就是编写getest.py处理这个响应，最简单的是返回一个位于屏幕中心的地标，代码如下：


#!C:/Python24/python.exe


#replace the line above with our own python path




import cgi




url = cgi.FieldStorage()


bbox = url['BBOX'].value


bbox = bbox.split(',')


west = float(bbox[0])


south = float(bbox[1])


east = float(bbox[2])


north = float(bbox[3])




center_lng = ((east - west) / 2) + west


center_lat = ((north - south) / 2) + south




kml = (


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


'<kml xmlns="http://earth.google.com/kml/2.2"> '


'<Placemark> '


'<name>View-centered placemark</name> '


'<Point> '


'<coordinates>%.6f,%.6f</coordinates> '


'</Point> '


'</Placemark> '


'</kml>'


) %(center_lng, center_lat)




print 'Content-Type: application/vnd.google-earth.kml+xml '


print kml



我们也可以在getest.py中编写复杂的功能，比如从数据库中提取数据生成KML文件，然后返回客户端与GE的数据叠加。原理介绍，简单至上，就这么简单吧。

学习资料(摘自http://www.javaworld.com/javaworld/jw-11-2005/jw-1114-google.html)：

Resources


Download the source code that accompanies this article “Servlet-based Google Earth Tours”
http://www.javaworld.com/javaworld/jw-11-2005/google/jw-1114-google.zip

Cylindrical projection
http://mathworld.wolfram.com/CylindricalProjection.html

Google Earth API
http://code.google.com/apis.html#earth

Google Earth Community
http://bbs.keyhole.com/ubb/ubbthreads.php/Cat/0

Google Earth download
http://earth.google.com/download-earth.html

Google Earth homepage
http://earth.google.com/

Hibernate framework
http://www.hibernate.org/

iBATIS framework
http://ibatis.apache.org/index.html

Jamon framework
http://www.jamon.org/Features.html

Microsoft Virtual Earth
http://virtualearth.msn.com/

Nasa World Wind
http://worldwind.arc.nasa.gov/

Google Earth KML Tutorial, where you'll find the algorithm for centering
http://www.keyhole.com/kml/kml_tut.html#tracking_point

For more articles on servlets, browse the Servlets section of JavaWorld's Topical Index
http://www.javaworld.com/channel_content/jw-servlets-index.shtml

For more articles on how to put your Java skills to work, browse the Applied Java section of JavaWorld's Topical Index
http://www.javaworld.com/channel_content/jw-applied-index.shtml