| Summary: | 碩士 === 國立成功大學 === 測量及空間資訊學系 === 106 === This study proposes a digital watermarking method for DEMs and contour maps. The method includes linear congruential generator(LCG), adaptive method, discrete cosine transform(DCT), discrete Fourier transform(DFT) and discrete wavelet transform(DWT). This study checks the robustness of watermarked DEM by using median filter, mean filter, random noise and clip attacks and checks watermarked contour maps by using clip, reordering and random noise attacks. The results of watermarked DEM with the proposed method by means of DCT are shown below. Maximum RMS dZ of DEM is 0.75m which means watermarked DEM can meet our national requirements. The peak signal-to-noise ratio(PSNR) value of all DEMs are larger than 59dB which means watermark is invisible. The bit error rate(BER) value of destroyed watermarks are all less than 35.8%. For my cases, the value of BER means that watermark can resist the attacks caused by four attack methods mentioned above. The results of watermarked contour map also are shown below. Maximum RMS dXY is 0.13m and maximal horizontal shift of vertex is 0.25m which means it can meet our national requirements and watermark cannot be perceived by human eyes which means watermark is invisible. The BER value of clip attack is 38.5% which is maximal. It means that the proposed method is weak to resist the attack caused by clip attack. But other BER values are smaller than 15.8%, for my case, it means that the proposed method can resist the attacks caused by reordering and random noise.
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