**4. The foundation of an earthquake condition simulation and evaluation system**

Based on remote sensing image two-dimensional spatial information systems, interpretation and analysis has been the main means of seismic disaster assessment. Although twodimensional spatial information systems have the macroscopic and overall characteristics, it also has inevitable defects in the earthquake disaster assessment (Xiao et al, 2001, Li et al, 2007), such as in accurate expression of three-dimensional information, an inability to record non-uniform three-dimensional spatial entities, and a lack of a basis for uneven spatial entity description of lake water, landslides, collapsed buildings and so on. Therefore, it is necessary to establish an evaluation system based on three-dimensional spatial information of earthquake disaster information for analysis.

For the Wenchuan and Yushu earthquakes, using three-dimensional simulation and evaluation with advanced Earth observation technology, we established realistic 3D terrain model using the relatively sophisticated disaster assessment model and successfully created an earthquake disaster simulation and evaluation system. Based on multi-sensor, multitemporal, and multi-resolution remote sensing images and 1: 50,000 scale DEM data, we produced technology for large 3D terrain modeling and interactive real-time rendering. The 3D simulation system provides a more intuitive disaster analysis method for major collapse, landslide, and debris flow disasters. Using red-blue 3D imaging techniques to get airborne remote sensing stereo images and reconstruct three-dimensional scenes, we can efficiently extract data on damage to housing and improve the disaster analysis accuracy using red and blue stereo glasses. In a 3D environment, not only can the geo-spatial relationship between objects be shown, but also the topological relations between spatial objects. Practice has proven that this kind of three-dimensional assessment is more efficient and reliable.

### **4.1 Three-dimensional terrain modeling and visualization**

We use 1: 50,000 topographic vector data of the disaster area for error analysis and to eliminate gross errors of contour and control point data. We use a difference algorithm for vector contour data to obtain high-resolution DEM raster data. In order to rebuild 3D virtual scenes, we use a merging method of aerial remote sensing images and Landsat TM images to generate the terrain texture. In severe disaster areas, we acquired highresolution data, TM images. Then combined with DEM data, the aerial remote sensing data can be corrected precisely. Finally, the merging of aviation data and TM data yield the an image of the entire area, which is then mapped to the three-dimensional terrain model to form a virtual 3D environment.

The complicated terrain of earthquake-stricken areas and large data of three-dimension model after overlaying images and DEM have brought challenges for real-time rendering. This paper proposes a multi-resolution triangular grid dynamic geographic model based on computing vision, established a simplified algorithm based on multi-resolution vision. Using a multi-resolution scene model algorithm, this paper resolves the real-time interactive roaming difficulty of large-scale three-dimensional terrain data. First, according to the

Earth Observation for Earthquake Disaster Monitoring and Assessment 309

The overlap rate between two adjacent high-resolution images of the disaster area from airborne remote sensing is high. Using this characteristic and remote sensing image processing, the images can generate red and blue stereopairs. Through red and blue stereo glasses, they can show the 3D Spatial Information of buildings in the disaster area intuitively and greatly improve the identification and extraction efficiency of housing damage information. The identification accuracy of semi-damaged buildings increases to

(a) (b)

Fig. 8. (a) 3D analysis of secondary geological disasters in the Wenchuan earthquake, (b) 3D

Remote sensing monitoring of the Wenchuan and Yushu earthquakes' secondary geological disaster shows that high-resolution optical remote sensing, which can extract the seismic secondary disaster remote sensing characteristics accurately and monitor and evaluate the information of spatial distribution, damage degree and so on of earthquake secondary geological disasters has some advantages, such as intuition, large information and quantification. SAR has the advantages of all-weather data acquisition. The Yushu earthquake multi-mode SAR remote sensing monitoring study has proven that multi-mode SAR is effect and has important potential in earthquake disaster analysis and evaluation. Three-dimensional computing technology for measuring secondary geological disasters is an important technology, which not only improves the calculation and simulation accuracy of secondary geological disasters, but also can promote collaboration on three-dimensional simulation technology and auxiliary mitigation and provide analysis platforms for

In addition, quantitative and reliable evaluation of secondary earthquake disaster depends on high-resolution Earth observation technology. But at present the automatic disaster monitoring algorithms and software for high-resolution Earth observation images still cannot meet actual needs, and 3D interactive analysis platform technology is still not mature. Meanwhile, secondary geological disaster monitoring relies heavily on traditional

view in red-blue mode for damaged building extraction.

interactive operation in secondary geological disasters.

man-machine interactive visual interpretation technology.

more than 10%.

**5. Conclusion** 

amount of data and resolution of images, the magnitude *n* is established. According to the given format, a model file of different resolutions is generated, and then when modeling real-time rending, a series of irregular grids is used to imitate the terrain. According to their distance from the point of view and complexity of the terrain, we choose the relevant resolution terrain model within sight of the study area that is the closest to the view point. The more complex the terrain is, the higher the terrain series are, the more triangle grids in the drawing area, the more sophisticated the display terrain, and the higher the resolution. Conversely, if the view point is farther away or the terrain is flat, the series of the topography of the area shows will be lower, the number of mesh triangles will be fewer, the terrain rougher, and the resolution lower. Thus, minimizing the number of triangles and reducing memory consumption can make the images and models have identical effects or gaps in a given range, closest to the real terrain.

In this paper we take the improved adaptive quaternary tree to construct layers of details. The quaternary tree index and the grading mode of organization management for largescale three-dimensional scenes can provide the chance for real-time interactive roaming analysis. In order to ensure the smoothness of scene rendering, we adopt a pre-loaded cache before the scene into the visible range. Then based on real-time rendering of the scene's rectangular range and the quaternary tree index, we can access related scenes' serial numbers quickly, which can be pre-loaded into memory. The scheduling management strategy can improve the rendering efficiency significantly, achieve real time, interactive terrain rendering, and improve the efficiency of disaster evaluation and analysis in the 3D environment.

#### **4.2 Three-dimensional terrain modeling and visualization**

Exposed areas along the river valley include a regional north-east-trending thrust fault. The area exhibits many faults and tectonites, which are weak and vulnerable and form the detachment surfaces. Due to the earthquake's physical destruction combined with heavy rain, a large number of landslides, mud-rock flows, and other geological disasters occurred. Our system provides a qualitative and quantitative analysis and monitoring of these secondary disasters. A 3D system for the analysis of secondary disasters has the following advantages:


One example is a statistical analysis of the secondary disaster in Chenjiaba. High-resolution aerial remote sensing images from May 28 were integrated into the system. The system gives information on landslides and mud-rock flows in the area from Beichuan County, Zhixin Village, to Pingwu County Yaogouli. The study identifies the Chenjiaba section landslide debris and other secondary geological disasters as the most serious. The system also marks the distribution of the disaster and builds disaster level categories. There is a total of 135 landslides, covering an area of 508 square kilometers, 38 dilapidations, covering 75.6 square kilometers, and 9 mud-rock flows covering an area of 23.9 square kilometers.

The overlap rate between two adjacent high-resolution images of the disaster area from airborne remote sensing is high. Using this characteristic and remote sensing image processing, the images can generate red and blue stereopairs. Through red and blue stereo glasses, they can show the 3D Spatial Information of buildings in the disaster area intuitively and greatly improve the identification and extraction efficiency of housing damage information. The identification accuracy of semi-damaged buildings increases to more than 10%.

Fig. 8. (a) 3D analysis of secondary geological disasters in the Wenchuan earthquake, (b) 3D view in red-blue mode for damaged building extraction.
