高清晰度电视的基本概念实际上并不是提高每个单元域的清晰度，而更多是提高图像中包括的可视域的百分比。
The basic concept behind high-definition television is actually not to increase the definition per unit area… but rather to increase the percentage of the visual field contained by the image.
对基于DEM数据库的可视域分析，该算法在时间复杂度较低的情况下大大减少了访问数据库的次数，取得了很好的效果。
For viewshed analysis based on DEM database, the algorithm having a good experimental effect reduces obviously the frequency of access to database with lower time complexity.
对基于DEM数据库的可视域分析，该算法在时间复杂度较低的情况下大大减少了访问数据库的次数，取得了很好的效果。
For viewshed analysis based on DEM database, the algorithm having a good experimental effect reduces obviously the frequency of access to database with lower time complexity.
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