根據著作權法與國家機密保護法規定，DEM與等高線圖的著作者享有其著作權且高精度的DEM以及等高線圖需要受到保護，因此DEM與等高線圖的數位浮水印技術有其研究的價值。
離散餘弦轉換(DCT)、離散傅立葉轉換(DFT)及離散小波轉換(DWT)為浮水印技術中常用的演算法，本研究提出以線性同餘法(LCG)產生密鑰並根據坡度分級與高程起伏量調整浮水印的嵌入強度，來設計出一種新的浮水印嵌入方法，並探討本研究提出的嵌入方法搭配三種演算法應用於DEM數位浮水印時的效果，再嘗試將DEM的測試經驗應用在等高線圖上，最後透過峰值信號噪訊比(PSNR)、均方根誤差(RMSD)及最大誤差來評估浮水印的成效，並進行攻擊測試，以位元錯誤率(BER)來檢視浮水印技術抵抗攻擊的能力。
實驗成果顯示本研究提出的方法，在DEM受到攻擊後萃取出的浮水印皆能以人眼辨識時，以DFT作為演算法造成的RMS dZ最小，山區、丘陵及平地分別為1.50m、0.51m及0.02m，分別佔實驗區高程起伏量的0.08%、0.10%及0.09%，抵抗破壞的能力最差，除了裁切攻擊外的BER最大值為25.6%；以哈爾小波作為演算法造成的RMS dZ最大，山區、丘陵及平地分別為3.35m、1.13m及0.05m，分別佔實驗區高程起伏量的0.18%、0.23%及0.23%，抵抗破壞的能力最好，除了裁切攻擊外的BER最大值為15.1%；DCT的表現介於前面兩者之間，對DEM造成的RMS dZ在山區、丘陵及平地分別為1.88m、0.64m及0.03m，分別佔實驗區高程起伏量的0.10%、0.13%及0.14%，除了裁切攻擊外的BER最大值為20.1%，而基於DCT的嵌入法對DEM造成的RMS dZ，在山區、丘陵及平原分別可以降低到0.75m、0.44m及0.01m，分別佔實驗區高程起伏量的0.04%、0.09%及0.05%，能夠符合國家規範，PSNR皆大於59dB，代表浮水印不可視，受到攻擊後浮水印的BER值皆小於35.8%，以本研究的實驗案例來說浮水印具有強韌性；而基於DCT的嵌入法對等高線圖造成的RMS dXY最大值為0.13m，節點的最大平面位移量為0.25m，受到攻擊後浮水印的BER值最大為38.5%，抵抗裁切破壞的能力較差，但能夠抵抗重新排列以及隨機亂數攻擊。

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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