项目基金:国家自然科学基金项目41471377、41531179、41421001;科技部基础研究计划项目2014FY121100;资源与环境信息系统国家重点实验室"结合大数据和抽样的空间制图"项目088RA200YA.[ Foundation items:National Natural Science Foundation of China, No.41471377, 41531179, 41421001;The Program Grant in Fundamental Re-search from the Ministry of Science and Technology, No.2014FY121100;LREIS, No.088RA200YA. ]