栅格数据金字塔是空间信息系统中的一类基本组织结构,基于小波的金字塔构建方法需要考虑数据分块导致的边界问题,现有算法或者未考虑边界问题,或者在消除边界缝隙问题时需增加大量的计算。针对分块数据小波变换的边界问题,提出分块数据的小波系数拼接算法,该算法对相邻子块边界系数进行叠加,使拼接后的小波系数等效于直接对大数据进行小波变换。在此基础上,提出无缝栅格数据小波金字塔构建方法:首先对大块数据进行分块多级小波变换,然后利用小波系数拼接算法完成对各块系数的无缝拼接。该金字塔结构消除了边界系数,实现了各子带小波系数的无缝组织。实验结果表明,拼接算法可大幅减少高层金字塔的数据量,且易于实现。

A raster data pyramid is a basic data structure in spatial information systems.The boundary issue caused by blocking must be considered in a wavelet-based pyramid construction method.This issue is not mentioned in most existing algorithms or a large amount of calculations is needed to eliminate the border gap in those other methods.This paper presents a wavelet coefficient stitching algorithm for data blocks,which addresses the block boundaries in the wavelet transformation.The key point of our stitching algorithm is that one block coefficients is patched by its adjoining blocks boundary coefficients.The stitching result is equivalent to proceeding wavelet transformation on the whole data.A pyramid construction method is proposed that is named seamless wavelet pyramid construction method (SWPCM).In the SWPCM,the whole data is divided into a large number of blocks and a wavelet transformation is performed on each block.Then,the stitching algorithm is executed on the blocks' wavelet coefficients.The boundary coefficients are eliminated and data seamless organization is achieved with SWPCM.The experiments show that the stitching algorithm can significantly reduce the sizes of high level coefficients and that the proposed method is easy to implement.