基于BP神经网络的坐标转换

BP神经网络是一个能以任意精度逼近的非线性映射系统,能削弱坐标转换中的非线性因素的影响,削弱坐标转换中系统误差和其他异常误差影响,提高坐标转换精度。通过实例证明,BP神经网络能有效削弱数据中的系统误差影响,提高独立坐标向1980西安坐标系的转换精度,但还存在一些不足,有待继续探究。     

地图扫描矢量化误差的最小二乘配置法处理研究

屏幕扫描数字化是地图数字化的常用方法。在数字化过程中,由于地图本身的变形、扫描仪分辨率等系统误差会影响数字化的结果。仿射变换是实现栅格数据向矢量化数据转换的常用方法之一,研究表明基于最小二乘的仿射变换只可以消除整体变形,而不能消除局部变形。为此作者提出采用最小二乘配置。采用最小二乘配置可以在计算转换参数的同时估计局部系统变形信号,可以消除或减弱以上误差的影响,改善数字化精度。实例分析表明,是提高扫描数字化的有效方法。     

数字化曲线的最小二乘配置

针对数字化地图的特点,提出用最小二乘配置的理论来估计拟合曲线的参数,给出一套计算方法.主要内容包括将纵横坐标均看作是观测值,综合处理偶然误差和系统误差的联合影响.采用数字化地图上位置误差的方差-协方差函数来作为信号的协方差阵,使得到的结果更为合理和简便.     

地图数字化的精度评定与控制

地图数字化不可避免地会产生误差，定量分析或减弱地图扫描数字化误差的影响，是地图数字化必须解决的问题。对于系统误差，我们采用函数模型(多项式)拟合，对于异常误差采用抗差估计。针对一幅具体的数字地图，我们分别用最小二乘拟合和抗差拟合分别求得了系统误差模型系数估计值，并给出了内、外检核精度。     

双因子抗差贝叶斯估计及其在GIS数据采集质量控制中的应用

在对GIS扫描数字化过程中,所采集的数据里经常含有系统误差和异常误差。在纠正这些误差的过程中,应同时考虑控制点坐标和数字化坐标的先验协因数。文中以数字化的系统误差拟合模型为例,提出双因子抗差贝叶斯估计误差拟合方法,并分别就控制点含有粗差、数字化点含有粗差和两者均含有粗差3种情况建立相应的模型,实例验证了其抗差效果。     

数字化地图的纠正模型及其优选

为了减弱或消除由于图纸变形、扫描数字化变形引起的GIS空间数据的系统误差,需要对数字化地图进行纠正。本文讨论了数字化地图纠正的概念模型,相似变换、仿射变换、多项式回归模型均是描述该概念模型的数学模型;重点研究了纠正模型的检验和优选问题,并用实例考察了纠正模型的优选及纠正的效果。     

立体坐标量测仪系统误差的测定与改正

本文探讨了立体坐标量测仪系统误差改正方法,及系统误差对观测值的影响。指出仪器准系统误差、归心安置定向误差是引起系统误差的主要原因。通过实验验证仿射变换改正公式对消除系统变形趋势有较好作用;同时高次多项式改正能提高更多的观测精度。利用最小二乘配置又可最后确定仪器的噪声影响,为评定仪器精度提供了依据。     

惯导系统横向坐标法导航性能研究

针对惯导系统横向坐标法,推导了惯导横向坐标系下的系统误差方程,通过求解静基座下的系统误差方程,研究了系统初始误差和惯性测量元件误差对基于横向坐标法的惯导系统的影响,在此基础上完成了系统误差仿真,并与地理经纬坐标解算方法进行比较。理论分析及仿真结果表明:横向速度误差、水平姿态误差为周期震荡型误差,位置误差和航向误差为随时间增长的积累型误差;横向坐标系法可以有效解决惯导地理经纬坐标解算方法的计算奇异和系统误差过大的问题。     

线扫描式机载LiDAR系统误差影响分析研究

机载LiDAR系统会受到多种误差源的影响,系统误差会给激光脚点的坐标带来系统偏差。针对安置向量误差、安置角误差、激光测距误差以及扫描角尺度因子误差这几种重要误差源,从机载LiDAR系统几何定位方程出发,推导了机载LiDAR系统误差影响计算公式,并结合模拟实验,分别研究了这几类误差源对激光脚点定位精度的影响规律,从理论上分析了各类误差对机载LiDAR系统定位精度的综合作用。文中的结果为设计系统检校方法并消除这些系统误差的影响提供理论依据,具有重要的参考价值。     

数字化曲线的附加系统参数平差

针对一般地图数字化曲线拟合方法的不足,提出了利用附加系统参数平差计算拟合曲线的参数。在参数平差中,将数字化曲线的X坐标和Y坐标均看作观测值,综合处理偶然误差和系统误差的联合影响,并评定精度。用t分布对系统参数进行显著性检验,结果表明附加系统参数模型正确。     

Completeness and classification correctness of features on topographic maps: An analysis of the estonian basic map

In an increasingly GIS‐literate world, the availability of quality topographic maps and map databases is critical for the numerous users of spatial data. Particularly governmental agencies, first responders, and utility and transportation services, rely on the completeness and classification correctness of these maps. Estonia has systematically updated its topographic Basic Map in digital form over the past 15 years. An analysis of the Estonian production process in the period 2003‐2006 provides a useful case study of both error types and error frequencies encountered in topographic mapping. Errors of completeness and classification correctness of topographic features are analyzed at two levels of specificity: in general, across all map sheets, and in detail according to the field‐workers who performed the mapping. The structure of errors at the two levels was different by geometry and error types; however, both systematic and individual errors were evident. The systematic errors indicated a need for revision and improvement of the data capture specifications, which was accomplished. The individual errors were addressed by additional training for the field‐workers involved.     

GIS空间数据质量控制的抗差拟合推估法

拟合推估法可用于拟合系统误差,削弱随机误差的影响,提高空间数据质量。与正常拟合推估法不同,提出了一种抗差拟合推估法以控制GIS空间数据的系统误差和异常误差的影响。在此基础上,提出了对剩余残差再拟合的思想,从而对拟合推估剩余系统误差进行控制。利用该方法,一方面可以有效地抵制系统误差的影响,另一方面又可以较好地遏制异常误差的污染。此外,对因协方差函数误差导致的信号估计偏差,也具有一定的补偿能力。最后通过实际计算与分析验证了该方法的有效性。     

数字地图在车辆导航中应用的若干技术问题

分析了对各种车辆导航系统对数字地图的使用需求，提出了车辆导航专用数字地图的特点和建立车辆导航专用数字地图库的必要性，在此基础上对数字地图在车辆导航中的若干技术问题作了一些探讨，并提出了一种在大范围内实现路径规划的技术途径。     

Use of local and global maps of forest canopy height and aboveground biomass to enhance local estimates of biomass in miombo woodlands in Tanzania

Field surveys are often a primary source of aboveground biomass (AGB) data, but plot-based estimates of parameters related to AGB are often not sufficiently precise, particularly not in tropical countries. Remotely sensed data may complement field data and thus help to increase the precision of estimates and circumvent some of the problems with missing sample observations in inaccessible areas. Here, we report the results of a study conducted in a 15,867 km² area in the dry miombo woodlands of Tanzania, to quantify the contribution of existing canopy height and biomass maps to improving the precision of canopy height and AGB estimates locally. A local and a global height map and three global biomass maps, and a probability sample of 513 inventory plots were subject to analysis. Model-assisted sampling estimators were used to estimate mean height and AGB across the study area using the original maps and then with the maps calibrated with local inventory plots. Large systematic map errors – positive or negative – were found for all the maps, with systematic errors as great as 60–70 %. After being calibrated locally, the maps contributed substantially to increasing the precision of both mean height and mean AGB estimates, with relative efficiencies (variance of the field-based estimates relative to the variance of the map-assisted estimates) of 1.3–2.7 for the overall estimates. The study, although focused on a relatively small area of dry tropical forests, illustrates the potential strengths and weaknesses of existing global forest height and biomass maps based on remotely sensed data and universal prediction models. Our results suggest that the use of regional or local inventory data for calibration can substantially increase the precision of map-based estimates and their applications in assessing forest carbon stocks for emission reduction programs and policy and financial decisions.     

Use of local and global maps of forest canopy height and aboveground biomass to enhance local estimates of biomass in miombo woodlands in Tanzania

Field surveys are often a primary source of aboveground biomass (AGB) data, but plot-based estimates of parameters related to AGB are often not sufficiently precise, particularly not in tropical countries. Remotely sensed data may complement field data and thus help to increase the precision of estimates and circumvent some of the problems with missing sample observations in inaccessible areas. Here, we report the results of a study conducted in a 15,867 km² area in the dry miombo woodlands of Tanzania, to quantify the contribution of existing canopy height and biomass maps to improving the precision of canopy height and AGB estimates locally. A local and a global height map and three global biomass maps, and a probability sample of 513 inventory plots were subject to analysis. Model-assisted sampling estimators were used to estimate mean height and AGB across the study area using the original maps and then with the maps calibrated with local inventory plots. Large systematic map errors – positive or negative – were found for all the maps, with systematic errors as great as 60–70 %. The maps contributed nothing or even negatively to the precision of mean height and mean AGB estimates. However, after being calibrated locally, the maps contributed substantially to increasing the precision of both mean height and mean AGB estimates, with relative efficiencies (variance of the field-based estimates relative to the variance of the map-assisted estimates) of 1.3–2.7 for the overall estimates. The study, although focused on a relatively small area of dry tropical forests, illustrates the potential strengths and weaknesses of existing global forest height and biomass maps based on remotely sensed data and universal prediction models. Our results suggest that the use of regional or local inventory data for calibration can substantially increase the precision of map-based estimates and their applications in assessing forest carbon stocks for emission reduction programs and policy and financial decisions.     

Mapping trees in high resolution imagery across large areas using locally variable thresholds guided by medium resolution tree maps

Large area tree maps, important for environmental monitoring and natural resource management, are often based on medium resolution satellite imagery. These data have difficulty in detecting trees in fragmented woodlands, and have significant omission errors in modified agricultural areas. High resolution imagery can better detect these trees, however, as most high resolution imagery is not normalised it is difficult to automate a tree classification method over large areas. The method developed here used an existing medium resolution map derived from either Landsat or SPOT5 satellite imagery to guide the classification of the high resolution imagery. It selected a spatially-variable threshold on the green band, calculated based on the spatially-variable percentage of trees in the existing map of tree cover. The green band proved more consistent at classifying trees across different images than several common band combinations. The method was tested on 0.5 m resolution imagery from airborne digital sensor (ADS) imagery across New South Wales (NSW), Australia using both Landsat and SPOT5 derived tree maps to guide the threshold selection. Accuracy was assessed across 6 large image mosaics revealing a more accurate result when the more accurate tree map from SPOT5 imagery was used. The resulting maps achieved an overall accuracy with 95% confidence intervals of 93% (90–95%), while the overall accuracy of the previous SPOT5 tree map was 87% (86–89%). The method reduced omission errors by mapping more scattered trees, although it did increase commission errors caused by dark pixels from water, building shadows, topographic shadows, and some soils and crops. The method allows trees to be automatically mapped at 5 m resolution from high resolution imagery, provided a medium resolution tree map already exists.     

数字地图的理论、方法和技术体系探讨

本文探讨数字地图的理论、方法和技术体系,既介绍研究心得,更意在诚邀专家学者的合作。在理论体系方面,本文章阐述了数字地图的概念、体系结构、理论基础,以及数字地图带来的地图学新观念。在方法体系方面,文章阐述了数字地图能够解决的地学问题、数字地图的分析方法、数字地图的数据模型;在技术体系方面,文章阐述了数字地图制图系统、移动数字地图技术等内容。文章给出了数字地图的应用实例,包括国家自然地图集数据库、电子版、网络版,以及中国科学院资源环境数据库电子地图集等两内容。     

基于纸质地图的单像地形图快速数字修测系统

提出了一种基于纸质地形图的单像地形图数字修测方法,它能在不具有矢量地形图的地区,根据新摄取的航摄像片直接对原有的地形图分版图的扫描影像进行修测,然后用绘图输出修测后的像素地图,或用于ＧＩＳ中相应数据的更新。     

地质图几何校正流程探讨

目前,地图的扫描数字化已成为GIS领域中获取数据信息的主要手段之一。应用MapGIS6.7软件,以丰富理论知识及大量实践为基础,对原始扫描地图进行校正过程中发现的一些问题及解决方案进行探讨,最后得出一套较为科学准确的地质图校正的方法流程。