| 摘要 |
PROBLEM TO BE SOLVED: To provide an electronic watermark imbedding method that is immune to various modification operations such as rotation, magnification/reduction, appending, and segmentation to vector map data, thereby an imbedded electronic watermark being hardly eliminated or falsified and to provide an electronic watermark extract method. SOLUTION: An electronic watermark module 100 divides one line segment of vector map data 105 stored in a map server 106 into line segments (101) and imbeds an electronic watermark, which is encrypted according to its division ratio, to the vector map data (102-104) so as to imbed the electronic watermark to the vector map data.
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