摘要
对常规线性四叉树编码方法存在的不足进行了分析 ,提出了一种在遍历栅格数据过程中直接生成四叉树的快速动态编码方法。该方法用栈代替线性表或数组 ,在提取格网单元后 ,直接检测其属性值 ,生成十进制Morton码。将这些数据压入栈 ,在栈中同步地对已检测过的格网单元或结点向上层结点进行合并。当对整个栅格数据遍历完后 ,栈中剩下的记录就是所需要的线性四叉树编码结果。最后根据测试结果比较了动态编码与常规编码方法的运行效率和内存占用量。结果表明 。
Raster data structure is one of the effective data structures to express spatial data.When raster data structure is used,the smaller the size of pixel or grid cell is,the higher resolving power of spatial data comes and the more cells with the same attribute value.This structure causes a large amount of redundant information.It is essential to compress the original raster data for the purpose of reducing the amount of data storage and the requirement of memory resource during data processing. Linear quadtree encoding is one of the significant compressing and organizing approaches for raster data.It transforms the primal raster data into a linear table.In the table,there are two columns that represent respectively the decimal Morton codes which denote the location and size of the leaf nodes of the quadtree and their corresponding attribute values.Two different traditional methods can be used to construct the linear table.They are linear_table method and pseudo_code method respectively.Both of the two methods are time_consuming and require large memory blocks when a huge raster data file is processed.It is necessary to investigate a new,fast and effective data compressing method to suit for huge raster data.Due to disadvantages of the two traditional linear quadtree encoding methods,a fast dynamic linear quadtree encoding approach (FDLQE) is put forward in this paper.This method can construct linear quadtree directly through only once tracing of the whole raster data.It uses a dynamic stack instead of linear table or one_dimensional array.FDLQE takes the decimal Morton code and its corresponding attribute value of a pixel or a homogeneous region as a record.It once uses a 2×2 window to extract 4 sequential pixels from the original raster data according to their decimal Morton codes,compares whether their attribute values are the same.If the attribute values of the pixels are the same,the 4 pixels can be combined into a node and the smallest decimal Morton code and its corresponding attribute value are pushed into
出处
《武汉测绘科技大学学报》
CSCD
2000年第4期324-328,共5页
Geomatics and Information Science of Wuhan University
基金
国家自然科学基金资助项目!(49871069)
教育部博士点基金资助项目!(97029005)
