Songshan Yue

Prototyping an open environment for sharing geographical analysis models on cloud computing platform

Abstract The sharing of geographical analysis models is of crucial importance for simulating geographic processes and phenomena in the current geographical information systems (e.g. Digital Earth), but there remain some issues that have not been completely resolved. The challenges include, eliminating model heterogeneity and searching for suitable infrastructures to support the open sharing and effective execution of models. Taking advantage of cloud computing, this article aims to address the above issues and develop an open environment for geographical analysis model sharing. On the basis of the analysis of the applicability of cloud computing, the architecture of the open environment is proposed. More importantly, key strategies designed for heterogeneous model description, model encapsulating as well as model deploying and transparent accessing in the cloud are discussed in detail to establish such an environment. Finally, the prototype environment is implemented, and experiments were conducted to verify the environments feasibility to support the sharing of geographical analysis models.

A data description model for reusing, sharing and integrating geo-analysis models

Geo-analysis models are necessary tools for understanding various geo-processes and phenomena in Earth’s environment. Studying, reusing, sharing and integrating geo-analysis models can help researchers solve complicated and synthetic geo-problems with interdisciplinary knowledge, especially for researchers who collaborate with each other to build virtual geographic environments (VGEs). While the integration frameworks of geo-analysis models could permit their practical use, it is essential for model users to prepare data according to the specific requirements of the different geo-analysis models. Model users should invest adequate effort and time into preparing such model data, particularly when employing multi-disciplinary geo-analysis models. This paper proposed a data description model, the Universal Data eXchange (UDX) model that can reduce the effort and difficulties of model data preparation and pre-processing for model users. With the UDX model, researchers from interdiscipline can build a collaborative workspace in VGEs more conveniently. A hierarchical structure was employed in the UDX model for the flexible description of heterogeneous model data, and a set of basic data node types was designed to provide a relatively stable organization method for the various data contents. In the UDX model, the structural format data (e.g., the Shapefile and NetCDF data) and the flexible plain text data content can be described in a uniform way. In addition, model data information can be completely and unambiguously described with the items in the attachment libraries (e.g., unit and dimension library, semantic library, spatial reference library, and data description template library). Furthermore, two different model integration case studies were conducted to prove that various data processing methods and efforts can be accumulated and organized with the designed UDX data processing library.

A function-based linear map symbol building and rendering method using shader language

Maps are widely used to visualize geo-information so that map users can develop related understandings about the real world. Such a process for communicating information is largely dependent on the rendering of map elements using different symbols (points and linear and area symbols). To meet the demand of more dynamic and comprehensive visualization in map rendering, it is essential to improve the rendering efficiency. This paper focuses on these research topics, especially the difficulty in constructing and drawing linear map symbols. By employing shader language, a function-based linear symbol building and rendering method is presented in this paper. The basic idea of this function-based method is to build a map-rendering solution that employs graphic processing unit (GPU) acceleration technology to improve the rendering efficiency. A ‘function’ is used to represent the algorithm that draws certain simple or complex linear map symbols. This function reflects the structure of a linear map symbol (describing the symbol construction information) and also the rendering process of the symbolized linear map elements (handled on a per-pixel basis by the shader program). Based on the Open Geospatial Consortium (OGC), Styled Layer Descriptor (SLD) specifications, four basic line types (i.e., solid lines, dashed lines, gradient color lines, and transition lines) are implemented in the proposed method, and the implementation of line markers, line joins and line caps is also discussed. Three experiments are conducted to demonstrate improvements in map rendering. The results show that a variety of linear map symbols can be constructed in a uniform way, which suggests that the proposed method addresses the difficulty in drawing linear map symbols. With this method, the efficiency of rendering linear map elements is substantially improved compared to using the graphics device interface plus (GDI+) and anti-grain geometry (AGG) methods; it also provides an applicable approach for developing map rendering systems. Using this function-based concept, the complexity of building linear map symbols and drawing linear map elements can be decreased.

A progressive transmission strategy for GIS vector data under the precondition of pixel losslessness

It is well known that the final results of geographic information system (GIS) mapping are composed of rasterized pixels in most display devices. Based on this, pixel equivalence is proposed as two vector data that can produce the same raster image on a device under the same mapping processes and parameters. Moreover, if between the two data, one is considered the original data and the other is its reduced-quantity version, then the latter can be regarded as pixel losslessness relative to the former. In this case, the reduced-quantity version can be used instead of the original data to produce the same result from the perspective of visualization. The aim of this article is to explore how to produce the transmitted data, including an initial code and a series of increments that are used for progressive transmission, to retain pixel losslessness. By illustrating that the vector data can be represented by a vertex or ordered sequence of vertices, this article introduces the detailed concepts of pixel equivalence and pixel losslessness of vector data. Then, the requirements for pixel equivalence between two vertices are deduced by analyzing the coordinate transform processes under specific assumptions. The method to generate an initial code and a series of increments related to a single vertex is proposed to produce vertices that are pixel equivalence to the original vertex under different coordinate transform processes. By discussing the traversing mode of the ordered sequence of vertices based on quadtree cells, a coding algorithm is proposed to develop the progressive transmission related to the multi-vertex and to generate reduced-quantity versions to retain pixel losslessness. Finally, experiments are designed to demonstrate that, under the precondition of pixel losslessness, the proposed progressive transmission method can significantly reduce the amount of transmitted data in the network environment.

Geographic scenario: a possible foundation for further development of virtual geographic environments

ABSTRACT It has been two decades since virtual geographic environments (VGEs) were initially proposed. While relevant theories and technologies are evolving, data organization models have always been the foundation of VGE development, and they require further exploration. Based on the comprehensive consideration of the characteristics of VGEs, geographic scene is proposed to organize geographic information and data. We empirically find that geographic scene provides a suitable organization schema to support geo-visualization, geo-simulation, and geo-collaboration. To systematically investigate the concept and method of geographic scene, Geographic Scenario is proposed as the theory on developing geographic scene, and corresponding key issues of the Geographic Scenario are illustrated in this article. Prospects of the proposed method are discussed with the hope of informing future studies of VGEs.

A model-service deployment strategy for collaboratively sharing geo-analysis models in an open web environment

ABSTRACT Geo-analysis models can be shared and reused via model-services to support more effective responses to risks and help to build a sustainable world. The deployment of model-services typically requires significant effort, primarily because of the complexity and disciplinary specifics of geo-analysis models. Various modelling participants engage in the collaborative modelling process: geo-analysis model resources are provided by model providers, computational resources are provided by computational resource providers, and the published model-services are accessed by model users. This paper primarily focuses on model-service deployment, with the basic goal of providing a collaboration-oriented method for modelling participants to conveniently work together and make full use of modelling and computational resources across an open web environment. For model resource providers, a model-deployment description method is studied to help build model-deployment packages; for computational resource providers, a computational resource description method is studied to help build model-service containers and connectors. An experimental system for sharing and reusing geo-analysis models is built to verify the capability and feasibility of the proposed methods. Through this strategy, modellers from dispersed regions can work together more easily, thus providing dynamic and reliable geospatial information for Future Earth studies.

A characteristic bitmap coding method for vector elements based on self-adaptive gridding

Spatial index is a key component of Geographic Information Systems (GISystems). To date, an increasing number of spatial indexes have been developed to enhance the efficiency of spatial analysis and spatial query. Approximate expressions are adopted in the foundation of spatial index construction, to assist data organisation, e.g., bounding box of vector elements can be employed to build R-tree index. However, R-tree index using such bounding box expresses elements approximately, which usually results in redundancy and excessiveness due to inherent roughness of this method. This study proposes a characteristic bitmap coding method, termed the QCODE method, which generates approximate expressions of vector elements based on self-adaptive gridding. Based on the sizes of vector elements, this method selects the grid at an appropriate level in a self-adaptive manner, discretises the vector elements into grids through a rasterisation operation, as well as compresses and encodes this information as the code of a characteristic bitmap, i.e., the QCODE. The ‘bit’ data type is used in the design of QCODE to restrict the approximate expression of vector elements into finite bytes, providing more precise filtering as compared to the case in which only bounding box is used. With its distinct characteristics, the QCODE is introduced for the improvement of R-tree index. The results of experiments show that, combined with R-tree index, this method can reduce the filtering amount of vector elements as required for spatial analysis, and accelerate the execution efficiency of the entire process of GIS spatial analysis.

A Procedural Construction Method for Interactive Map Symbols Used for Disasters and Emergency Response

The timely and accurate mapping of dynamic disasters and emergencies is an important task that is necessary for supporting the decision-making that can improve the efficiency of rescue and response efforts. The existing emergency symbol libraries are primarily composed of point symbols and simple line symbols, focusing on the representation of disasters, related facilities, and operations. However, various existing response factors (e.g., the distribution and types of emergency forces) are also important for further decision-making and emergency responses; there is a need to design complex and diverse symbols to represent this rich information. Moreover, traditional mapping systems only provide static map symbols that cannot be easily edited after creation, making it difficult to support interactive editing after the symbols are mapped, thus hindering the representation of dynamic disasters and response factors. This article targets a solution of the above issues by proposing a procedural construction method of interactive map symbols for dynamic disasters and emergency responses. There are two primary research points. First, an emergency response and decision symbol library was classified and integrated into the existing attachments to form a richer symbol library for comprehensively representing disasters and emergencies. Second, an interactive map symbol procedural construction method was designed based on (1) primitive geometric compositions and geometric graphics algorithms to construct the map symbol graphics; (2) an interactive graphics control and drawing attributes configuration method to support user interactive editing of the visual variables of the mapped symbols; (3) and a dynamic updating and drawing strategy to support the real-time refreshing of the changing visual variables. The experiment was conducted using the Wenchuan earthquake as a case study, and the results demonstrate a powerful capacity of the produced interactive map symbols, which will contribute to the improvement of the mapping efficiency and representation capability of disasters and emergency response.

A Representation Method for Complex Road Networks in Virtual Geographic Environments

Road networks are important for modelling the urban geographic environment. It is necessary to determine the spatial relationships of road intersections when using maps to help researchers conduct virtual urban geographic experiments (because a road intersection might occur as a connected cross or as an unconnected bridge overpass). Based on the concept of using different map layers to organize the render order of each road segment, three methods (manual, semi-automatic and mask-based automatic) are available to help map designers arrange the rendering order. However, significant efforts are still needed, and rendering efficiency remains problematic with these methods. This paper considers the Discrete, Crossing, Overpass, Underpass, Conjunction, Up-overlap and Down-overlap spatial relationships of road intersections. An automatic method is proposed to represent these spatial relationships when drawing road networks on a map. The data-layer organization method (reflecting road grade and elevation-level information) and the symbol-layer decomposition method (reflecting road covering order in the vertical direction) are designed to determine the rendering order of each road element when rendering a map. In addition, an “auxiliary-drawing-action” (for drawing road segments belonging to different grades and elevations) is proposed to adjust the rendering sequences automatically. Two experiments are conducted to demonstrate the feasibility and efficiency of the method, and the results demonstrate that it can effectively handle spatial relationships of road networks in map representations. Using the proposed method, the difficulty of rendering complex road networks can be reduced.

Construction of collaborative mapping engine for dynamic disaster and emergency response

In the collaborative mapping of disasters, response situations and decisions, it is important to support various emergency responders with a unified platform to help in decision making and coordinating emergency action. However, most existing symbol libraries focus primarily on representing disasters and related information. These libraries lack specific symbols to map response situations and emergency decisions. For representation of dynamic disasters and response factors, these symbols support rich interactive editing after the symbols are mapped. In addition, decision making and mapping of disasters and response situations typically involve different domains of expertise and different responsibilities of map makers. It is essential to construct a collaborative mapping engine that supports disaster and emergency mapping on a collaborative platform. However, most existing methods of collaboration cannot readily support collaboration on symbols containing complex data structures or accommodate rich interactive editing operations. This article proposes a collaborative mapping engine for dynamic disasters and emergency responses. To support collaborative mapping based on complex data structures and rich interactive map symbols, it proposes a method of mapping operation replication to implement collaboration. Additionally, strategies were designed to enhance the efficiency and stability of collaboration. Finally, an experiment was conducted using the Wenchuan earthquake as an example. The results reveal that the engine can contribute to improved mapping efficiency and management during emergencies.