最小二乘内插数学模型生成虚拟地形的可视化研究

数字高程模型 可视化 最小二乘 OpenGL （digital elevation model; visualization; least squares ; OpenGL）
【文 摘】本文通过对最小二乘内插数学模型的分析和研究,利用搜索圆的搜索方法,运用C44语言和OpenGL动态连接库将采集的离散点生成DEM数据,实现了由二维平面上的等高线到三维虚拟地形的可视化,并对可视化效果进行了比较和分析。可视化结果表明,此算法速度快且效果好。此研究成果对虚拟战场环境的生成有一定参考价值。     

Remote sensing of structural complexity indices for habitat and species distribution modeling

Spatial distribution models are increasingly used in ecological studies, but are limited by the poor accuracy of remote sensing (RS) for mapping microhabitat (< 0.1 ha) features. Mapping accuracy can be improved by combining advanced RS image-processing techniques with microhabitat data expressed as a structural complexity index (SCI). To test this idea, we used principal components analysis (PCA) and an additive SCI method developed for forest ecology (calculated by re-scaling and summing representative structural variables) to summarize 13 microhabitat-scale (0.04 ha) vegetation structure attributes describing the rare mountain bongo antelope's (Tragelaphus eurycerus isaaci) habitat in Kenya's Aberdare mountains. Microhabitat data were collected in 127 plots: 37 related to bongo habitat use, 90 from 1 km-spaced grid points representing overall habitat availability and bongo non-presence. We then assessed each SCI's effectiveness for discerning microhabitat variability and bongo habitat selection, using Wilcoxon Rank Sum tests for differences in mean SCI scores among plots divided into 4 vegetation classes, and the Area Under the Curve (AUC) of receiver operating characteristics from logistic regressions. We also examined the accuracy of predicted SCI scores resulting from regression models based on variables derived from a) ASTER imagery processed with spectral mixture and texture analysis, b) an SRTM DEM and c) rainfall data, using the 90 grid plots for model training and the bongo plots as an independent test dataset. Of the five SCIs derived, two performed best: the PCA-derived Canopy Structure Index (CSI) and an additive index summarizing 8 structural variables (AI₈). CSI and AI₈ showed significant differences between 5 of 6 vegetation class pairs, strong abilities to distinguish bongo-selected from available habitat (AUCs = 0.71 (CSI); 0.70 (AI₈)), and predicted scores 60-110% more accurate than reported by other studies using RS to quantify individual microhabitat structural attributes (CSI model R² = 0.51, RMSE = 0.19 (training) and 0.21 (test); AI₈ model R² = 0.46, RMSE = 0.17 (training) and 0.19 (test)). Repeating the Wilcoxon tests and logistic regressions with RS-predicted SCI values showed that AI₈ most effectively preserved the patterns found with the observed SCIs. These results demonstrate that SCIs effectively characterize microhabitat structure and selection, and boost microhabitat mapping accuracy when combined with enhanced RS image-processing techniques. This approach can improve distribution models and broaden their applicability, makes RS more relevant to applied ecology, and shows that processing field data to be more compatible with RS can improve RS-based habitat mapping accuracy.     

利用QAR和DEM的机载气象雷达地杂波仿真方法

地杂波是降低机载气象雷达性能的一个关键因素。利用数字高程模型（Digital elevation model,DEM）精确计算不同地形的电磁散射时,本文提出了将经纬度变化量转换成距离变化量的方法,简化计算,并修正了俯角和擦地角计算。然后根据气象雷达方程建模地杂波,按照WXR-2100的实际参数设置雷达参数,结合快速存取记录器（Quick access recorder,QAR）反演的航班飞行参数,分别高保真地仿真了起飞和巡航两个阶段机载气象雷达不同工作模式下的杂波图,反映了实际的运行情况,最后建立了杂波图数据库。     

Crusta: A new virtual globe for real-time visualization of sub-meter digital topography at planetary scales

Virtual globes are becoming ubiquitous in the visualization of planetary bodies and Earth specifically. While many of the current virtual globes have proven to be quite useful for remote geologic investigation, they were never designed for the purpose of serving as virtual geologic instruments. Their shortcomings have become more obvious as earth scientists struggle to visualize recently released digital elevation models of very high spatial resolution (0.5-1 m²/sample) and extent (>2000 km²). We developed Crusta as an alternative virtual globe that allows users to easily visualize their custom imagery and more importantly their custom topography. Crusta represents the globe as a 30-sided polyhedron to avoid distortion of the display, in particular the singularities at the poles characteristic of other projections. This polyhedron defines 30 “base patches,” each being a four-sided region that can be subdivided to an arbitrarily fine grid on the surface of the globe to accommodate input data of arbitrary resolution, from global (BlueMarble) to local (tripod LiDAR), all in the same visualization. We designed Crusta to be dynamic with the shading of the terrain surface computed on-the-fly when a user manipulates his point-of-view. In a similarly interactive fashion the globe's surface can be exaggerated vertically. The combination of the two effects greatly improves the perception of shape. A convenient pre-processing tool based on the GDAL library facilitates importing a number of data formats into the Crusta-specific multi-scale hierarchies that enable interactive visualization on a range of platforms from laptops to immersive geowalls and caves. The main scientific user community for Crusta is earth scientists, and their needs have been driving the development.     

An algorithm for generalizing topography to grids while preserving subscale morphologic characteristics—creating a glacier bed DEM for Jakobshavn trough as low-resolution input for dynamic ice-sheet models

The objective of this paper is to derive an algorithm for preserving important subscale morphologic characteristics at grids of lower-resolution, in particular for linear features such as canyons and ridge lines. The development of such an algorithm is necessitated by applications that require reduced spatial resolution, as is common in cartographic generalization, GIS applications, and geophysical modeling. Since any algorithm that results in weighted averages, including optimum interpolation and ordinary kriging, cannot reproduce correct depths, a new algorithm is designed based on principles of mathematical morphology. The algorithm described here is applied to derive a subglacial bed of the Greenland Ice Sheet that includes the trough of Jakobshavn Isbræ as a continuous canyon at correct depth in a low-resolution (5-km) digital elevation model (DEM). Data from recent airborne radar measurements of the elevation of the subglacial bed as part of the CReSIS project are utilized. The morphologic algorithm is designed with geophysical ice-sheet modeling in mind, in the following context. Currently occurring changes in the Earth's climate and the cryosphere cause changes in sea level, and the societal relevance of these natural processes motivates estimation of maximal sea-level rise in the medium-term future. The fast-moving outlet glaciers are more sensitive to climatic change than other parts of the Greenland ice sheet. Jakobshavn Isbrae, the fastest-moving ice stream in Greenland, follows a subglacial geologic trough. Since the existence of the trough causes the acceleration of the slow-moving inland ice in the Jakobshavn region and the formation of the ice stream, correct representation of the trough in a DEM is essential to model changes in the dynamics of the ice sheet and resultant sea-level predictions, even if current ice-sheet models can typically be run only at 5-km resolution. The DEM resultant from this study helps to bridge the conceptual gap between data analysis and geophysical modeling approaches. It is available as SeaRISE Greenland bed data set dev1.2 at http://websrv.cs.umt.edu/isis/index.php/SeaRISE_Assessment.     

A fast and robust bulk-loading algorithm for indexing very large digital elevation datasets: I. Algorithm

Digital elevation models (DEMs) constitute a valuable source of data for a number of geoscience-related applications. The Shuttle Radar Topography Mission (SRTM) collected and made available to the public the world's largest DEM (composed of billions of points) until that date. The SRTM DEM is stored on the NASA repository as a well-organized collection of flat files. The retrieval of this stored topographic information about a region of interest involves one selection of a proper list of files, their downloading, data filtering in the desired region, and their processing according to user needs. With the aim to provide an easier and faster access to this data by improving its further analysis and processing, we have indexed the SRTM DEM by means of a spatial indexing based on the kd-tree data structure, called the Q-tree. This paper is the first in a two-part series that describes the method followed to build an index on such huge amounts of data, minimizing the number of insert operations. We demonstrate that our method can build a very efficient space-partitioning index, with good performance in both point and range queries on the spatial data. To the best of our knowledge, this is the only successful spatial indexing proposal in the literature that deals with such a huge volume of data.     

低空突防用数字地形数据压缩研究

地形数据是低空突防系统最主要的信息来源之一,由于机载条件对电子设备的重量和体积有很大的限制,因此地形数据必须按低空防的要求进行压缩以减小其存储空间,本文探讨并比较了采用。ＬＰＣ,ＤＣＴ和ＢＴＣ三种压缩算法运行低空防用地形数据压缩的特点,文中首先设计了一个三阶预测器对地形数据进行ＬＰＣ压缩,其次给出了ＤＣＴ编码的恢复误差的估计式,并根据该估计式按低空防要求选取量化矩阵以压缩地形数据,最后提出了一种块间自适应的ＢＴＣ算法,仿真结果表明,块间自适应ＢＴＣ算法的综合压缩的性能较合乎低空突防的要求。     

基于IMAGIS农村地理信息系统的设计与实现

随着社会主义新农村建设的不断深入,农村人民生活水平的不断提高,新农村的规划和管理也相应的提高到一个新的层次。运用现代技术手段提高新农村发展规划水平和建设的可视化效果,本文结合适普公司IMAGIS软件,对新农村建设的三维场景问题进行讨论,并且根据三维地理信息系统的原理和方法来建立农村的三维模型场景,给出了系统空间数据和属性数据的管理方法。     

基于小波神经网络的GPS高程异常拟合模型探究

利用GPS进行高程测量具有很多优越性,高精度地确定高程异常对于用GPS高程测量部分代替普通几何水准测量具有重要意义。依据BP神经网络和小波神经网络的基本原理,利用实验数据证实了小波神经网络模型比BP神经网络模型和文献[6]模型在GPS高程异常拟合中具有更高的精度,说明小波神经网络在GPS高程异常拟合中具有较强的实用性。