基于NMEA 0183的GPS设备轨迹恢复方法

APPROACH OF TRAJECTORY RECOVERY FROM GPS DEVICES BASED ON NMEA 0183

针对GPS设备的轨迹恢复问题,由于传统的文件恢复方法依赖于系统元信息,一旦元信息受损、不可读或重新分配等原因就会恢复失败。借助文件雕复的思想提出一种基于NMEA 0183协议的GPS设备轨迹恢复方法,可以在系统元信息不可用的前提下恢复出GPS设备上的轨迹日志数据。首先利用轨迹数据的特征从镜像中定位到所有属于NMEA日志的数据块。再根据日志数据在时间和空间上的局部连续性以及日志的结构特征设计一个判别器,对所有已定位的数据块使用重组算法恢复出日志。最后再根据相应的格式对恢复出的日志进行解析,重构出被删除的行车轨迹。实验结果表明,在数据镜像完整、系统元信息不可用、日志文件高度分片、日志数据部分覆写的情况下恢复率能够保持在99%以上,并且能够兼容不同簇大小的文件系统。

For the problem of trajectory recovery from GPS devices, since traditional recovery method relies on system metadata, it will be failed if the metadata is damaged, unreadable or reallocated. An approach of trajectory recovery from GPS devices based on NMEA 0183 protocol is proposed according to the idea of file carving, which can successfully recover the track log data under the condition that metadata is unavailable. At first, all the data blocks belonging to the NMEA log were pinpointed by using the characteristics of track data. Then, a discriminator was designed according to the time and space continuity of log data and some structural characteristics. The obtained data blocks were reconstructed into new logs by leveraging a reassembly algorithm. Finally, the deleted trajectories were reconstructed by analyzing the recovered logs according to the NMEA formats. The experimental results show that the recovery rate can be maintained above 99% in the cases of complete forensic image, unavailable metadata image, extremely fragmented image and data overwriting. In addition, it is also compatible with various file systems of different cluster sizes.