Spatial Vector Data Compression Method Based on Integer Wavelet Transform
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摘要: 针对空间曲线矢量数据相邻坐标点间坐标值大小差别不大的特点，提出一种新的矢量数据压缩方法：首先将空间坐标点间的差值转换为整型的偏移量，使用偏移量表示矢量数据的坐标点；然后利用整数小波变换(IWT)处理偏移量序列，最后对变换后的小波系数进行无损熵编码.使用此方法对中国数字地理地图数据的SHP文件进行压缩，实验结果显示, 压缩比超过11，高于其他类似方法，表明本压缩方法能够实现较高压缩比的空间矢量数据无损压缩.Abstract: The curve vector data are characterized by small differences between coordinate values of adjacent points. So in this paper, differences between the coordinate values are converted to the integer offset and then the offset is used as the substitute for coordinates of vector data. The integer offset sequence is processed by integer wavelet transform and then lossless entropy coding is used to compress the wavelet coefficients. Compressing the China's digital geographic map data of SHP files by the presented method generates a compression ratio higher than 11. Experimental results show that, for the vector data lossless compression, the presented compression method can achieve a higher compression ratio than other similar methods.
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表 1 浮点数矢量数据整型化
Table 1. Transforming float of vector data into integer
数据点编号 原始矢量数据坐标点 坐标值偏移量表示 偏移量整数化 X坐标 Y坐标 X坐标 Y坐标 X坐标 Y坐标 1 122.095 0 52.033 7 0 0 0 0 2 122.075 1 52.038 8 -0.019 9 0.005 1 -199 51 3 122.058 1 52.038 3 -0.017 0 -0.000 5 -170 -5 4 122.049 3 52.037 0 -0.008 8 -0.001 3 -88 -13 5 122.045 8 52.035 2 -0.003 5 -0.001 8 -35 -18 6 122.045 7 52.032 7 -0.000 1 -0.002 5 -1 -25 7 122.055 2 52.018 5 0.009 5 -0.014 2 95 -142 8 122.056 5 52.010 7 0.001 3 -0.007 8 13 -78 9 122.058 1 52.002 8 0.001 6 -0.007 9 16 -79 10 122.060 3 52.000 0 0.002 2 -0.002 8 22 -28 11 122.063 4 51.996 1 0.003 1 -0.003 9 31 -39 12 122.064 7 51.990 2 0.001 3 -0.005 9 13 -59 13 122.063 0 51.986 3 -0.001 7 -0.003 9 -17 -39 14 122.059 8 51.982 8 -0.003 2 -0.003 5 -32 -35 15 122.053 1 51.982 1 -0.006 7 -0.000 7 -67 -7 16 122.048 3 51.981 1 -0.004 8 -0.001 0 -48 -10 17 122.041 7 51.980 3 -0.006 6 -0.000 8 -66 -8 18 122.034 3 51.978 4 -0.007 4 -0.001 9 -74 -19 19 122.028 6 51.973 3 -0.005 7 -0.005 1 -57 -51 20 122.024 4 51.966 4 -0.004 2 -0.006 9 -42 -69 21 122.021 2 51.959 1 -0.003 2 -0.007 3 -32 -73 22 122.013 7 51.950 6 -0.007 5 -0.008 5 -75 -85 23 122.008 3 51.945 9 -0.005 4 -0.004 7 -54 -47 24 122.003 3 51.943 1 -0.005 0 -0.002 8 -50 -28 25 121.996 8 51.942 3 -0.006 5 -0.000 8 -65 -8 26 121.993 8 51.942 2 -0.003 0 -0.000 1 -30 -1 27 121.986 1 51.937 2 -0.007 8 -0.005 0 -78 -50 28 121.975 9 51.930 7 -0.010 2 -0.006 5 -102 -65 
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表 2 矢量数据压缩结果
Table 2. Vector data compression results
实验数据 原始数据大小(kb) 压缩后数据大小(kb) 压缩比 roa_4m.shp 583 54 10.8 rai_4m.shp 753 67 11.2 bou1_4l.shp 1 142 101 11.3 hyd1_4l.shp 1 151 101 11.4 hyd1_4p.shp 933 86 10.9
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