Dual watermarking method for trajectory data based on robust watermarking and fragile watermarking

A dual watermarking device for trajectory data based on robust watermarking and fragile watermarking, comprising:

• a first acquiring part, configured to acquire a robust watermark;
• a second acquiring part, configured to acquire a fragile watermark;
• a first embedding part, configured to embed the robust watermark;
• wherein a process of embedding the robust watermark by the first embedding part comprises:
• based on the robust watermark, setting a preset time threshold and a preset distance threshold for each trajectory of a trajectory dataset;
• and in response to a time difference between two trajectory points adjacent in time of the trajectory of the trajectory dataset being greater than the preset time threshold or a distance difference between the two trajectory points adjacent in time of the trajectory of the trajectory dataset being greater than the preset distance threshold, segmenting the trajectory into sub-trajectories;
• compressing each of the sub-trajectories of the trajectory dataset to obtain feature points of each trajectory of the trajectory dataset, thereby to obtain a feature point set FP of the trajectory dataset, calculating a minimum convex hull of the feature point set FP and obtaining a farthest pair of feature points in the minimum convex hull, setting feature points in the farthest pair of feature points as constant points, taking a feature point of the constant points with a smaller trajectory sequence number as a first constant point pf(xf, yf), and taking another feature point of the constant points as a second constant point ps(xs, ys);
• calculating each angle α defined by each feature point except the constant points in the feature point set FP, the first constant point pf, and the second constant point ps;
• and calculating each distance ratio r defined by each feature point except the constant points in the feature point set FP, the first constant point pf, and the second constant point ps;
• using each angle α and each distance ratio r as input values of a hash function to generate an index of a to-be-embedded robust watermark bit of each corresponding feature point except the constant points in the feature point set FP in the robust watermark Wr, and acquiring the to-be-embedded robust watermark bit of each corresponding feature point except the constant points in the feature point set/P according to the index;
• and
• embedding the to-be-embedded robust watermark bit of each corresponding feature point except the constant points in the feature point set FP into a δ-th decimal place of each angle α;
• and
• a second embedding part, configured to embed the fragile watermark;
• wherein a process of embedding the fragile watermark by the second embedding part comprises:
• calculating each angle defined by each trajectory point of the trajectory dataset, the first constant point pf, and the second constant point ps;
• calculating each distance ratio defined by each trajectory point of the trajectory dataset, the first constant point pf, and the second constant point ps;
• combining each angle and each distance ratio to map each angle and each distance ratio on integers [1, k];
• and grouping trajectory points of the trajectory dataset with a same mapping value into a corresponding one group to thereby obtain a grouping result V={V1, . . . , Vk} of the trajectory points of the trajectory dataset, and k represents the number of groups of the grouping result;
• and
• traversing each group of the grouping result V and embedding the fragile watermark into trajectory points in each group except the constant points.