JPEG压缩对摄影测量点定位精度的影响

Abstract

对某城区一对 1∶80 0 0航摄立体数字影像利用Intergraph数字摄影测量工作站上的立体量测软件IS DM进行手工量测 ,然后通过用自行开发的GPS辅助光束法区域网平差软件WuCAPSGPS的单模型光束法平差精确测定了 18个加密点的位置。经过对数字影像采用 1到 10 0不同质量因子的JPEG压缩 ,获得一组质量各异的压缩影像 ,从分析重建影像点定位结果的变化入手 ,探讨了JPEG压缩对摄影测量点定位精度的影响。试验表明 :失真JPEG压缩对摄影测量点定位精度的影响是显著的。随着压缩比的增大 ,影像可视化质量逐渐衰减 ,像点量测精度不断降低 ,加密点位精度几乎呈线性趋势下降 ,且高程比平面衰减的速度要快得多 This paper is to investigate empirically the accuracy effects of photogrammetric point determination (PPD) using digital aerial stereo images with different level of JPEG compression as well as the suitability of adopting JPEG standard to compress digital aerial images. A pair of aerial black_white photos with 1∶8000 scale taken from a city proper was selected and scanned at a resolution of 25μm. We measured 18 image points with ISDM (Image Station Digital Mensuration) of Intergraph digital photogrammetric workstation and performed the bundle adjustment by single model with WuCAPS\-\{GPS\} (Wuhan GPS_supported bundle block adjustment) developed by the authors. In processing various JPEG compressed images with Q _factors from 1 to 100, the accuracy of the 3D coordinates of photogrammetric points was assessed and compared. The empirical results have shown that, when the compression ratios are under 10, the visual quality of JPEG compressed images is excellent and the accuracy of manual image mensuration is not influenced in essence. Although the significant differences of 3D coordinates of pass points are found in the bundle adjustment with different JPEG compressed images, the resulting accuracy of PPD will also meet the requirement for most photogrammetric applications. Therefore, a compression ratio of 10 could be recommended for photogrammetric point determination.