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When users zoom in or out on a digital map, the map should change correspondingly to present geographical information at proper levels. A way to help map users better keep track of their interested objects is to change the map smoothly instead of discretely switching between several levels of detail. This paper focuses on the problem of providing smooth merging of area objects. We propose to merge multiple areas simultaneously to share their animation durations. In this way, each merging operation can be prolonged, and it is visually smoother. We present a greedy algorithm to decide which areas should be merged at each step. The merging process is pre-computed and is recorded into a space-scale cube (SSC). When a user accesses our web map, the SSC is sent to the client side so that the map can be generated by slicing the SSC in the graphics processing unit (GPU). We also explain how to snap the zooming to valid states so that the zooming will not stop halfway of the merging operations. Our case study shows that it is visually smoother to merge simultaneously than to sequentially merge each pair of areas.

海底地貌数据与人类认知海洋、探索海洋、利用海洋息息相关, 海底地貌数据综合是海图编制、海洋空间数据处理的重点研究内容之一。海底地貌数据综合属于地图综合的研究范畴, 但受历史渊源、学科体系、应用范畴等诸多因素影响, 常被认为是地图综合中相对独立、特殊的研究内容。本文在明确海底地貌数据综合特殊性的基础上, 从数据增强、综合方法、质量评价3个方面梳理海底地貌数据综合研究进展, 归纳了几种常见的海底地貌数据综合应用案例, 并从研究内容、技术方法、实践应用3个方面探讨了海底地貌数据综合的发展趋势。

Digital Elevation Models (DEMs) are extensively utilized for terrain analysis, representation, and visualization. Various application scenarios require DEMs at different Level of Details (LODs). Although traditional multi-scale landform expression methods primarily target DEMs at small scales, the simplifying Digital Surface Models (DSMs) for urban modeling at large scales remains a significant challenge. By integrating map generalization theory with computer vision techniques, we developed a novel method for urban building simplification in DSMs, termed Building Simplification in Digital Surface Models (BS-DSM). First, the buildings extracted from the DSMs are subjected to morphological analysis and aligned to a specific orientation. Next, the DSMs are divided into rectangular pixel blocks through energy-driven sampling, followed by horizontal simplification of building shapes in a 2D projection plane according to the geometric characteristics of these pixel blocks. Finally, to preserve the average height and total volume of the simplified 3D buildings in the vertical direction, the building heights across different pixel blocks are adjusted and interpolated based on the skeleton lines of building roofs and calculations of adjacent height values. The proposed BS-DSM method was evaluated using the publicly available Vaihingen DSM dataset. The result shows that the BS-DSM method performs better in simplifying building shape and height while meeting basic multi-scale expression constraints compared with traditional filtering methods.

Building simplification involves the process of reducing the complexity of building shapes and details, which is crucial for preserving key features, highlighting essential information, and enhancing map readability. As the map scale decreases, the complex details of buildings need to be effectively simplified. Although various methods exist for simplifying vector or raster data buildings, there is limited research on retaining the original building textures during the simplification process. This study proposes a raster-based method for the simplification and texturing of buildings in remote sensing imagery. The method begins with segmenting preprocessed individual raster data buildings using the superpixels extracted via energy-driven sampling (SEEDS) superpixel segmentation method. Superpixels to be retained are then selected based on the evaluation parameters, corner ratio (CR), and square ratio (SR). Subsequently, the building area texture is extracted, and suitable textures from the texture library are selected through texture feature comparison (TFC). The selected textures are then hue-adjusted to achieve simplified textures that closely resemble the original image. Compared to traditional raster-based building simplification methods, this superpixel-based approach for the simplification and texturing of buildings in remote sensing imagery provides more suitable textures for simplified structures. This enhances the effectiveness of raster-based map generalization, improving both the aesthetic appeal and functionality of maps.

Cartographic generalization is a problem, which poses interesting challenges to automation. Whereas plenty of algorithms have been developed for the different sub-problems of generalization (e.g., simplification, displacement, aggregation), there are still cases, which are not generalized adequately or in a satisfactory way. The main problem is the interplay between different operators. In those cases the human operator is the benchmark, who is able to design an aesthetic and correct representation of the physical reality. Deep learning methods have shown tremendous success for interpretation problems for which algorithmic methods have deficits. A prominent example is the classification and interpretation of images, where deep learning approaches outperform traditional computer vision methods. In both domains-computer vision and cartography-humans are able to produce good solutions. A prerequisite for the application of deep learning is the availability of many representative training examples for the situation to be learned. As this is given in cartography (there are many existing map series), the idea in this paper is to employ deep convolutional neural networks (DCNNs) for cartographic generalizations tasks, especially for the task of building generalization. Three network architectures, namely U-net, residual U-net and generative adversarial network (GAN), are evaluated both quantitatively and qualitatively in this paper. They are compared based on their performance on this task at target map scales 1:10,000, 1:15,000 and 1:25,000, respectively. The results indicate that deep learning models can successfully learn cartographic generalization operations in one single model in an implicit way. The residual U-net outperforms the others and achieved the best generalization performance.

As web maps are now extensively used by billions of users, the energy consumption of these maps is not marginal anymore. Green cartography seeks to reduce the energy consumption of maps to promote more sustainable digital tools. To reduce energy consumption, we first need to better understand the different sources of energy consumption for web maps. Among these sources, this paper focuses on the tiles that are stored on servers and then constantly transferred each time a user explores the map. This paper presents several experiments carried out with current web maps to assess this energy consumption. We first try to assess the number of map tiles that are loaded through the web when users explore web maps, and we determine which types of interaction are used with the maps, and a similar amount of tiles is loaded. Then, we try to assess which zoom levels are the most loaded by users; it appears that the medium–large scales are the most used (between zoom levels 11 and 17). Then, we explore the size of the map tiles and try to assess which ones are larger and thus require more energy to load over the web; we can find clear differences between zoom levels. Finally, we discuss how map generalization could be used to reduce energy consumption by creating lighter tiles. These experiments show that the current web maps are suboptimal regarding energy consumption, with many tiles loaded at zoom levels where the tiles are larger than necessary.

The consistency of geospatial data is of great significance for the application and updating of geographic information in web maps. Due to the multiple data sources and different temporal versions, the tile web maps usually meet the inconsistency question across different layers. This study tries to develop a method to detect this kind of inconsistency utilizing a raster-based scaling approach. Compared with vector-based handling, this method can be directly available for multi-level tile images in a pixel representation form. The proposed cross-layer raster tile map rendering method (CRTMRM) consists of four primary aspects: geographic object separation, consistency rendering rules, data scaling and derivation with super-pixel segmentation, and inconsistency detection. The scale transformation strategy with the super-pixel attempts to obtain a simplified representation. Taking the scale lifespan variation and geometric consistency rules into account, the inconsistency detection of tile maps is conducted between temporal versions, multi-sources, and different scales through actual and derived data overlay analysis. The experiment focuses on features of cross-layer water or vegetation areas with Level 9 to Level 14 in Baidu Maps, Amap, and Google Maps. This method is able to serve as a basis for massive unstructured web map data inconsistency detection and support intelligent web map rendering.

Recognizing building group patterns is fundamental to numerous fields, such as urban landscape evaluation, social analysis, and map generalization. Despite the increasing number of algorithms available for building group pattern recognition, there is still a lack of satisfactory grouping results due to insufficient information and only geometric features being provided to recognition methods. This study aims to provide a novel building grouping method that combines building function and geometric information. We specifically focus on the process of recognizing building groups in topographic maps as a prerequisite to subsequent map generalization. First, the building functions are inferred using the dynamic time warping (DTW) algorithm based on Tencent user density data and POIs (points of interest). Then, two types of constrained Delaunay triangulations (CDTs) are created for each building block, from which several spatial indices, such as the continuity index (SCI), direction, and distance of every two adjacent buildings, are derived. Finally, each building block is modeled as a graph on the grounds of derived matrices and building function information, and a graph segmentation approach is proposed to extract building groups. A case study is conducted to test the proposed approach. The experimental results indicate that the proposed approach can produce satisfactory results, given that the correctness value is above 81.63% for our study area. Comparative studies reveal that the method without building function information is an ineffective grouping method when buildings with different functions are close to each other. In addition, generalization results derived from the proposed method are more in line with those of maps for daily use, as they provide users with more accurate spatial divisions of urban buildings.

As the complexity of GIS data continues to increase, there is a growing demand for automated map generalization. As end-to-end generative models, GAN models offer new solutions for automated map generalization. This study explores the impact of different map symbolization configurations on generative models, specifically using CycleGAN for line feature generalization. The quality of the generated results was assessed by constructing various symbolization datasets (line width, type, and color) and evaluating CycleGAN’s performance using metrics such as the MSE, SSIM, and PSNR. The results indicate that moderate line widths (0.5–1) yield better detail preservation, and different line types (framed lines and dashed lines) can highlight feature boundaries and enhance visual perception. By contrast, high-contrast color schemes enhance feature differentiation but increase pixel-level errors. This study concludes that generative models can maintain the geometric structure and spatial distribution of line features, but it is crucial to choose more suitable line features for different scenarios to meet detail requirements, ensuring high-quality outputs under diverse configurations.

P283.7; 为充分利用已有化简成果及其蕴含的化简知识,本文集成几种机器学习算法提出图形、图像融合利用的智能化简方法,实现顶点取舍决策的学习和优化.首先,分别利用全连接神经网络和卷积神经网络设计、构建基于图形的顶点取舍模型和基于图像的顶点取舍模型,通过样本训练各模型拟合从图形特征到顶点取舍和从栅格图像到顶点取舍的映射;然后,基于线性加权、朴素贝叶斯、支持向量机、人工神经网络构建多种融合决策模型,实现基于图形和基于图像的顶点取舍的融合利用;最后,通过试验用例对所有模型进行测试.试验结果表明:基于图形和基于图像的顶点取舍模型在一定程度上学习、掌握了化简算子,融合利用后还能进一步提高化简准确性、实现优势互补.