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Google Earth Engine ——数据全解析专辑(DEM-H: Australian SRTM Hydrologically Enforced Digital)澳大利亚1弧秒 DEM!

The Hydrologically Enforced Digital Elevation Model (DEM-H) was derived from the SRTM data acquired by NASA in February 2000. The model has been hydrologically conditioned and drainage enforced. The DEM-H captures flow paths based on SRTM elevations and mapped stream lines, and supports delineation of catchments and related hydrological attributes. The dataset was derived from the 1 second smoothed Digital Elevation Model (DEM-S; ANZCW0703014016) by enforcing hydrological connectivity with the ANUDEM software, using selected AusHydro V1.6 (February 2010) 1:250,000 scale watercourse lines (ANZCW0503900101) and lines derived from DEM-S to define the watercourses. The drainage enforcement has produced a consistent representation of hydrological connectivity with some elevation artefacts resulting from the drainage enforcement. A full description of the methods is in preparation (Dowling et al., in prep).

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ThreadLocal实现线程安全 转

Spring通过各种模板类降低了开发者使用各种数据持久技术的难度。这些模板类都是线程安全的,也就是说,多个DAO可以复用同一个模板实例而不会发生冲突。我们使用模板类访问底层数据,根据持久化技术的不同,模板类需要绑定数据连接或会话的资源。但这些资源本身是非线程安全的,也就是说它们不能在同一时刻被多个线程共享。虽然模板类通过资源池获取数据连接或会话,但资源池本身解决的是数据连接或会话的缓存问题,并非数据连接或会话的线程安全问题。  按照传统经验,如果某个对象是非线程安全的,在多线程环境下,对对象的访问必须采用synchronized进行线程同步。但模板类并未采用线程同步机制,因为线程同步会降低并发性,影响系统性能。此外,通过代码同步解决线程安全的挑战性很大,可能会增强好几倍的实现难度。那么模板类究竟仰仗何种魔法神功,可以在无须线程同步的情况下就化解线程安全的难题呢?答案就是ThreadLocal!  ThreadLocal在Spring中发挥着重要的作用,在管理request作用域的Bean、事务管理、任务调度、AOP等模块都出现了它们的身影,起着举足轻重的作用。

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