Study On The Integrated Generalization Of Relief And Water System Based On General DEM

Relief generalization is one of the most important parts in cartography. Relief exists in the real three dimension world, it is complexity and polymorphism makes its digitalization worked out as multiple products. Relief generalization is full of challenges.In this paper, we re-examine the issue of relief generalization in the viewpoint of 3D information carrier inside relief. Thus we extend all the relief modeling conception to general DEM. The general DEM is expected to unify the different forms of DEM which always behavior different after the operations of relief generalization. The general DEM is also compliant to the composition of relief information. The river systems wandering behind the ground can also be regarded to be part of terrain information. In this paper we just adopt the concept and innovatively put forward the proposal of the integrated generalization of relief and river systems, which is meaningful for settle the problem of morphologic conflicts between the generalization of relief and generalization of water system.This paper specifically in the follow six import researches:(1) The paper clarified the meaning and significance of the study, analyzed the challenges and new features of relief generalization, summarized the progress of this research field and focused on the results of the theoretical researches and the existing algorithms.(2) The paper analyzed the features of relief including the morphology three-dimensional topographic continuity, the complexity, the diversity, the spatial proximity and the uncertainty of its elements. Then it discussed modeling methods of current DEM. DEM is a model of information about relief, and also has the essential means for interpretation the geomorphologic features. So, this paper raises the point: Different DEM forms are only multi-state expression of the same three dimensional shape of the earth surface, under ideal conditions they should be a set of "same Heterogeneous quality" stuff. Thus, we put forward the concepts of the general DEM: (i) the DEMs expressed in varied forms should be equivalent in nature; (ii) irregular distribution of discrete points is the most general form, any other form of DEM can be looked as its special cases; (iii) When the general form of DEM is correctly generalized, any other form of DEM can also be generalized with the same precise.(3) In the viewpoint of "General", the DEM information should include all the elevation point. With start point, after discussing the three-dimensional relief generalization constraints and the existing DEM generalization conceptual framework, this paper proposed a model for the relief generalization based general DEM. The model includes four elements:(ⅰ) three dimensional topographic feature point selection, (ⅱ) the terrain constraints analysis, (ⅲ) the degree of automation and (ⅳ) the qualitative evaluation of the generalization results. The model particularly emphasized that the water system winding on the earth surface should be regarded as the constraint for the process of relief generalization. Flow path is a kind of important compensation to the three-dimensional relief information and can partly control the final result of relief morpho-simplification.(4) Based on the expatiation of implement mechanism of 3DDP algorithm for the feature points’extraction, we constituted the 3DDP algorithm systems for the relief generalization. Making use of the spatial approximation relation between the elevations, a series of optimization methods were proposed for some specific DEM, such as the scanning sorting method for the Grid DEM, the line wise sorting for the contour DEM, and global loneliness index for weight pseudo point-plane distance calculation. Furthermore, Trend plane model and the multi-view model were prompt based on the visual selection. With a case study, we successfully proved the well feasibility of 3DDP algorithms.(5) The harmonic spatial relations between the relief and the water system in the real world were discussed deeply. Their integrated combinations were summarized in three states:"river exists and so is the valley", "river vanish but valley exist" and "river vanish and so is the valley". Based on the semantic affinity of the stream physical characters and the 3D feature of the earth surface, the elevation points on the flow pathway can be viewed as the elevation points, namely a kind of general DEM. Therefore, the basic idea of integrated generalization of relief and water systems is brought forward. Based on the 3D relief generalization model, take the dendriform water systems for example; we advanced the framework integrated cartographic generalization of the relief and water system using 3DDP algorithm. The experiments show that this integrated generalization can simplify the spatial configuration of both relief form and the water systems, while keeping their harmonious relations.(6) The automated control on the generalization degree and the evaluation of the generalization results are two important portions in the relief generalization process. For the first issues, we advanced a new method named intelligent damping oscillation, which can automatically adjust the generalization threshold by twofold iterative level, one is the amount of data compression and the other is the amount of relief information. For the second issue, whereas the quality assessment of the results of the relief generalization is obviously subjective at present, we had some preliminary discussions on it. The quality assessment of the relief generalization should be based on the same abstracted level, and the better results relief should be the one which more approaches the original physiognomy. we also proposed the methods for the quantification of the relief information and the generalization results for the further study.