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Respected readers, authors and reviewers, you can add comments to this page on any questions about the contribution, review,        editing and publication of this journal. We will give you an answer as soon as possible. Thank you for your support! YAN Haowen, ZHANG Xingang, LU Xiaomin, LI Pengbo. Approach to automating the DP Algorithm—taking river simplification as an example[J]. Geomatics and Information Science of Wuhan University. doi: 10.13203/j.whugis20210412
 Citation: YAN Haowen, ZHANG Xingang, LU Xiaomin, LI Pengbo. Approach to automating the DP Algorithm—taking river simplification as an example[J]. Geomatics and Information Science of Wuhan University. # Approach to automating the DP Algorithm—taking river simplification as an example

##### doi: 10.13203/j.whugis20210412
Funds:

The National Natural Science Foundation of China (41930101).

• Received Date: 2022-07-13
Available Online: 2022-08-18 • Objectives: Curve simplification is of importance in automated map generalization; nevertheless, the Douglas-Peucker Algorithm (i.e., the DP Algorithm) popularly used in map generalization is not automatic, because a key parameter called distance tolerance (i.e.,ε) must be given by experienced cartographers and need to be input before execution of the algorithm. Methods: To solve the problem, this paper proposed a method to automatically calculate 𝜀 and by which the automation of the DP Algorithm is achieved. The method consists of the following steps:(1) A formula is constructed by the Hausdorff Distance for calculating the similarity degree (Sim) between a curve at a larger scale and its simplified counterpart at a smaller scale. (2) 15 linear rivers are selected, and each of them are manually simplified to get their counterparts at seven different scales. The Sim of each original river and each of its simplified counterpart at a smaller scale can be obtained using the formula constructed by the Hausdorff Distance, and 15×7=105 coordinate pairs consisting of (S, Sim) can be got, and a function between Sim and 𝑆 are constructed by the curve fitting using the coordinates. (3) In the meanwhile, the 15 rivers are simplified using a number of 𝜀, and the Sim of each original river and each of its simplified counterpart at a smaller scale can be calculated using the formula constructed by the Hausdorff Distance. In this way, a number of coordinate pairs (ε, Sim) are got, and a function between 𝜀 and Sim is constructed by the curve fitting. (4) By the function between Sim and S and that between 𝜀 and Sim, a formula between 𝜀 and 𝑆 can be deducted. Using the formula ε can be calculated automatically, because in a map generalization task 𝑆 is usually known. After this step, automation of the DP Algorithm is achieved. Results: The experiments have shown that (1) the proposed DP Algorithm can automatically simplify the rivers in a specific geographical area to get the results at different scales; and (2) the resulting river curves generated by the proposed DP Algorithm have a high degree of similarity with the ones made by experienced cartographers. Their average similarity degree is 0.927. Conclusion: The proposed DP algorithm can simplify curve features on maps automatically, and the results are highly intelligent and credible. Although only river data is tested in this paper, the principle of the proposed method can be extended to other linear features on maps. Our future work will be on improving the accuracy of the proposed DP Algorithm using more river data so that the algorithm can be used in practical map generalization engineering.
• ## Approach to automating the DP Algorithm—taking river simplification as an example

##### doi: 10.13203/j.whugis20210412
###### 1. Department of GIS, Faculty of Geomatics, Lanzhou Jiaotong University, Lanzhou 730070, China;2. National-local Joint Engineering Research Center of Technologies and Applications for National Geographic State Monitoring, Lanzhou 730070, China;3. Gansu Provincial Engineering Laboratory for National Geographic State Monitoring, Lanzhou 730070, China
Funds:

The National Natural Science Foundation of China (41930101).

Abstract: Objectives: Curve simplification is of importance in automated map generalization; nevertheless, the Douglas-Peucker Algorithm (i.e., the DP Algorithm) popularly used in map generalization is not automatic, because a key parameter called distance tolerance (i.e.,ε) must be given by experienced cartographers and need to be input before execution of the algorithm. Methods: To solve the problem, this paper proposed a method to automatically calculate 𝜀 and by which the automation of the DP Algorithm is achieved. The method consists of the following steps:(1) A formula is constructed by the Hausdorff Distance for calculating the similarity degree (Sim) between a curve at a larger scale and its simplified counterpart at a smaller scale. (2) 15 linear rivers are selected, and each of them are manually simplified to get their counterparts at seven different scales. The Sim of each original river and each of its simplified counterpart at a smaller scale can be obtained using the formula constructed by the Hausdorff Distance, and 15×7=105 coordinate pairs consisting of (S, Sim) can be got, and a function between Sim and 𝑆 are constructed by the curve fitting using the coordinates. (3) In the meanwhile, the 15 rivers are simplified using a number of 𝜀, and the Sim of each original river and each of its simplified counterpart at a smaller scale can be calculated using the formula constructed by the Hausdorff Distance. In this way, a number of coordinate pairs (ε, Sim) are got, and a function between 𝜀 and Sim is constructed by the curve fitting. (4) By the function between Sim and S and that between 𝜀 and Sim, a formula between 𝜀 and 𝑆 can be deducted. Using the formula ε can be calculated automatically, because in a map generalization task 𝑆 is usually known. After this step, automation of the DP Algorithm is achieved. Results: The experiments have shown that (1) the proposed DP Algorithm can automatically simplify the rivers in a specific geographical area to get the results at different scales; and (2) the resulting river curves generated by the proposed DP Algorithm have a high degree of similarity with the ones made by experienced cartographers. Their average similarity degree is 0.927. Conclusion: The proposed DP algorithm can simplify curve features on maps automatically, and the results are highly intelligent and credible. Although only river data is tested in this paper, the principle of the proposed method can be extended to other linear features on maps. Our future work will be on improving the accuracy of the proposed DP Algorithm using more river data so that the algorithm can be used in practical map generalization engineering.

YAN Haowen, ZHANG Xingang, LU Xiaomin, LI Pengbo. Approach to automating the DP Algorithm—taking river simplification as an example[J]. Geomatics and Information Science of Wuhan University. doi: 10.13203/j.whugis20210412
 Citation: YAN Haowen, ZHANG Xingang, LU Xiaomin, LI Pengbo. Approach to automating the DP Algorithm—taking river simplification as an example[J]. Geomatics and Information Science of Wuhan University. Reference (19)
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