3D urban Modeling Based on skyline

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3D urban Modeling Based on skyline

 

Since Gore proposed the concept of "Digital Earth", it has become a hot topic to express geographical space in digital form. Digital provinces and cities and digital towns have become the development strategies of developed provinces, cities, and regions in the 21st century, it has become one of the commanding heights of Technology, Industry, and economy. 3D Urban Landscape modeling is an important part of digital city construction. It is one of the research contents of photography measurement and remote sensing, geographic information system and computer science. The establishment of three-dimensional urban landscape will express and process geospatial information in a new way, and play an important role in urban planning, real estate development, traffic management, tourism and other fields.

With the rapid development of the information age, people are increasingly eager to express and process all kinds of three-dimensional information in the city. Not only do they need to express a single building or a group of buildings, but they also need to establish an overall urban landscape model, we also hope to use these models for urban planning and design, Emergency Command, and other work. However, it is difficult to quickly build a large-scale 3D model, and city 3D modeling is plagued by insufficient data resources. On the one hand, it is difficult for regular and simple buildings to express the real 3D world. On the other hand, fine modeling not only takes time and effort, but also brings a lot of difficulties to the system's visualization and spatial analysis in the later stages. In the development of digital regions, city virtual modeling often faces the challenge of "large data volume, heavy tasks, high hardware requirements, and long development cycle", which greatly limits the development of this field. Therefore, through comparative research and experiments, the author combines the existing methods to find a relatively economical and fast solution based on the characteristics of the urban landscape model, and uses the skyline software as a platform, taking xuchang City, Henan Province as the test zone, the construction of 3D urban landscape is completed, which provides an idea for the construction of 3D urban landscape. I believe it will be helpful to promote 3D urban Modeling in China.

 

 

1Research Status of 3D Modeling

At present, people have made a lot of research on 3D Urban Landscape modeling. In terms of technology, 3D modeling has roughly three implementation technologies: first, directly using 3D modeling software, software such as sketch up and 3dmax are used for modeling. The second is to directly use the two-dimensional line drawing data of traditional GIS and its corresponding HEIGHT attributes for 3D modeling. The corresponding textures can be added to the surface of each building; third, 3D modeling using digital photography and measurement technology. The first method can realistically represent the city's fine structure and material characteristics, but the model cannot represent the true geographical location, and the production requires a lot of manpower and material resources. The second method is more advantageous than the three-dimensional modeling of regular buildings. It does not have enough strength to express the precise nodes of the city, and the visual effect is not very good. The third method is currently relatively costly.

In the practical operation of 3D City modeling, it is difficult to quickly and effectively use one of the above technical methods in the face of a wide variety of object types and a large number of surface buildings, therefore, different technical methods are often used in combination, that is, three-dimensional modeling of multi-source data and multiple methods. For example, in the early days, people combined aerial images and DEM to build a city's terrain or architectural landscape model. Although this method is convenient and fast, the constructed buildings lack side textures and geometric information. On this basis, some scholars have proposed a method to build a three-dimensional city model based on the combination of 2 DGIS and DEM, but this method can only establish a more regular building model on the urban natural landscape, it is difficult to construct complex entities in cities, such as rivers, roads, afforestation, and municipal facilities. At present, many scholars have used sophisticated 3D modeling to reconstruct an object-based planar basemap data, aerial images, or terrestrial photographic images, although this modeling method can be used to create a precise and realistic 3D model, the entire modeling process requires manual operations and is less automated. Furthermore, this method creates a large amount of data for the model, which is not conducive to visualization and Spatial Analysis of 3du GIS. The 3D Modeling Method Based on geometric elements (CSG method) and the program-based modeling method is difficult to describe complex and Realistic 3D buildings due to the regularity constraints of geometric elements. It is mainly used in 3D games and military simulation that do not have strong requirements on realistic authenticity.

As a whole, the construction of the above three-dimensional model has become a bottleneck restricting the development of geographic information and digital city construction because of its poor visualization effect or low degree of automation.

 

2Data Preparation and technical routes

2.1Lab Area Overview

The sample area of the experiment is the old city of xuchang City, Henan Province. The area is 1.8 square kilometers, with thousands of individual buildings. The ancient and modern buildings in the area coexist, and there is a large area of water and green space, fully reflecting the complexity and diversity of general cities, it is very representative.

2.2Data Source

1) in the old city of xuchang city and its surrounding areas, the Topographic Map (DWG format) is used. The topographic map coordinate system adopted the Beijing Coordinate System in 500. The topographic map covers roads, water bodies, contour lines, buildings, and annotation information, the topographic map information was collected on January 1, 1998.

2) qucikbird high-resolution satellite image in the old city of xuchang city and its surrounding areas. The image imaging time is from January 1, 2005. The UTM projection coordinate system is used.

3) nearby digital photos of some buildings and other objects in the old city of xuchang city. The digital photos were taken on January 1, 2007.

2.3Software Configuration

The core application software is a series of Skyline software for 3D presentation and application development. The development environment is visual studio2005. There are four sets of auxiliary software. Their names and Main uses are: ArcGIS for processing and conversion of vector data; AutoCAD for Building Contour Extraction and Data Source processing; photoshop for texture image processing and processing; 3dsmax is used for 3D modeling of special buildings.

Skyline software is an excellent 3D geographic information system software. It consists of three independent subsystems: terrabuilder, terraexplorer pro, and terragate, these three subsystems can connect different geographic data and quickly distribute them to various users.

2.3.1 Terrabuilder

A large amount of image, elevation, and vector data are integrated to create a 3D model terrain database with precise coordinates.

2.3.2 Terraexplorer pro

It is a desktop application that allows users to browse and analyze spatial data and edit it. You can also add 2D or 3D objects, browsing paths, scenarios, and geographic information files. Terraw.e is connected to the terrain library created by terrabuilder and can be published on the network.

2.3.3 Terradevelease

It is a product in the terraexplorer family and can be used to customize customer requirements.

2.4Technical Route

The overall technical route is to load ouickbird satellite images and elevation data from the experimental area to the terrabuilder software of the skyline system, convert the data format, and then generate an MPT file, form the surface dataset required by the terraexplorer Pro Software of the skyline system. Next, in terraexplorer pro, load the surface dataset, import the vector dataset and related data, establish a two-dimensional and three-dimensional model, and then generate a real 3D city landscape. Figure 1 shows the specific technical route.

Figure 1 Technical Route of 3D City Modeling

 

33D City Model Establishment

3.1Terrain Modeling

Terrain Modeling is based on the DEM data of a region and overlays remote sensing images to display 3D terrain.

Process the DWG topographic map, delete unnecessary layers, retain only the layers of buildings, labels, lawns, road trees, and contour lines, and extract the contour lines, then, the contour data is interpolated to generate the terrain DEM. This process can be completed in AutoCAD and ArcGIS.

Correction and Projection Transformation of fast bird images, and color processing using Photoshop, so that they conform to the beautiful and natural principle, as the terrain texture or three-dimensional city "basemap ".

Load the terrain DEM and remote sensing images of coordinate system 1 to the terrabuilder software of Skyline series to generate *. MP format file, which is a terrain dataset that reflects the terrain fluctuations and expresses the real texture of the ground.

3.2Building Modeling

For 3D modeling of buildings in a large area, different types of buildings must be modeled separately to improve efficiency. The buildings in the city area are represented by simple textures. The main buildings along the street need to add photo textures Based on the blocks to enhance the sense of realism; 3dsmax can be used for separate modeling of complex or important landmark buildings with fine structures and textures. This process not only improves modeling efficiency, but also reduces the amount of data and facilitates the display and roaming of 3D scenes.

3.2.1 Modeling of Common Buildings

The topographic map is processed in AutoCAD, and unnecessary lines are deleted to reduce the data volume. Only the main and clear building outlines are left, and the data is imported into ArcGIS for topology check, close the contour lines of buildings that are not closed to ensure that the subsequent modeling can proceed smoothly. The processed building data and floor labeling information are spatial and associated with the building to assign floor attributes, the height of the building is calculated based on 3 meters on each layer. In this way, vector data including the plane profile data and elevation information of a building is obtained.

In the skyline series terraexplorer Pro software, load the previously generated terrain dataset, import the building vector data, and stretch the data according to the height attribute to obtain the building object block. Due to the time difference of the data source, a small number of buildings may not match the buildings displayed in the remote sensing basemap. You need to use the 3d-building function in terraexplorer pro, 3D modeling is performed on the location of a building to make the building object block consistent with the Remote Sensing basemap, with a simple and unified texture. This method can be used for modeling of a large number of buildings within a city plot.

3.2.2Texture ing

The meaning of texture can be simply summarized as: The image can be used to replace the simulated or non-simulated details in the entity model to improve the simulation fidelity and display speed. Building texture is an important part of the three-dimensional model of a building. Its quality determines the overall effect and texture details of the scene, and ultimately determines the degree of realism of the scene. Texture must be added for main buildings along the street to enhance the sense of realism.

The texture of a building consists of two parts: the side and the top, which are extracted by using near-scene digital photos and images. A large number of close-to-view photos of buildings are taken in the test area. close-to-view photos need to be processed in Photoshop. The basic operations such as cropping, splicing, free transformation, and stretching are mainly used. According to the experiment, we can conclude that it is best to save the processed photos in JPG format to reduce the data volume. At the same time, the image resolution should be adjusted to the power of 2, and the image size should be smaller than kb. The top textures of building models are collected from remote sensing images.

After processing the texture image, select the corresponding facade of the building along the street in the terraexplorer Pro software, map the texture, and add the texture to enhance the 3D representation of the city.

3.2.3Special Building

For buildings or landmarks with complex structures in the city, the automatic stretching method will cause serious distortion of buildings, such as ancient buildings, bridges, and large sculptures, such irregular objects and their landmark buildings must be independently modeled.

Separate modeling of these buildings in 3dmax, with refined structures and materials. Convert the created model to *. X or * FLT format. This is two 3D file formats supported by Skyline. The model files in these two formats are relatively small, facilitating loading and displaying. The conversion process requires third-party plug-ins. After the conversion format, the model file can be directly loaded into terraexplorer pro, and the location and relevant properties can be adjusted to complete the modeling of special buildings. There are about 10 buildings to be separately modeled in the test area.

3.2.4Other modeling components

The method of transparent texture is used for tree processing, rather than the three-dimensional model. The purpose of this method is mainly to consider the data volume. Currently, the common method is to use cross-area texture or a single texture to represent a single tree. This study uses a single texture. When this method is used, the display of trees is a billboard technology, that is, no matter how the scene rotates, the object is always facing the screen and observer. Although the texture image is relatively simple, this method saves data space as much as possible, and keeps the image more entertaining. The processing of roads and lawns can be relatively flexible, and can be expressed in a single color or in a real texture,

 

43D City Landscape Display

After loading the terrain dataset and adding vector data and the corresponding model, you can browse and roam the 3D Urban Landscape in terraexplorer pro. You can also perform secondary development, customize the interface and corresponding functions. In this study, the skyline series terradevelease development tool is used to implement the 3D display system in the old city of xuchang. Terradevelease provides a wide range of Custom Application customization functions in the form of ActiveX controls. In visual integrated development environment Visual studio2005, an independent 3D Visual application system can be developed by integrating all functions and custom interfaces of the terraexplorer Pro software system with the terradevelease development tool. In this system, you can perform basic roaming and navigation operations to view the three-dimensional landscape of the entire old city of xuchang. Its application interface 2 is shown.

 

 

5Summary

This paper proposes a complete urban 3D modeling solution. Firstly, this paper introduces the research status of 3D modeling, and then uses CAD topographic maps and remote sensing images as data sources and skyline software as a platform to complete 3D modeling in the old city of xuchang, finally, the 3D display system of the old city of xuchang is realized using the development kit provided by Skyline. The results show that this 3D modeling method is feasible. It can efficiently and quickly create a 3D Urban Landscape in large scenarios, intuitively and quickly display and browse 3D information, and meet the needs of 3D urban modeling. Currently, most of the terrain data of the Basic Surveying and Mapping Department is still in the DWG format. Using this method to build a three-dimensional urban landscape can save a lot of manpower and material resources, which is not only suitable for China's national conditions, it can also meet various needs and play an important role in demonstrating and guiding the speed of 3D virtual city digital community construction.