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Digital Terrain Modelling. 第 3 章 DTM 源数据获取技术. Contents. 3.1 Data sources for digital terrain modelling 3.2 Photogrammetry 3.3 Radargrammetry and SAR Interferometry 3.4 Airborne laser scanning (Lidar) 3.5 Cartographic digitisation 3.6 GPS for direct data acquisition;and - PowerPoint PPT Presentation
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Contents
3.1 Data sources for digital terrain modelling 3.2 Photogrammetry3.3 Radargrammetry and SAR Interferometry3.4 Airborne laser scanning (Lidar)3.5 Cartographic digitisation3.6 GPS for direct data acquisition;and 3.7 The comparison between DTM data from different sources
3.1 Data sources for digital terrain modelling Data sources means the materials from which data can be
acquired for terrain modelling DTM source data means data acquired from data sources of
digital terrain modelling
DEM Cost vs. Vertical Accuracy
Mercer, 2004
Uni
t Pric
e( U
S $
/ km
2 )
Increasing Detail
$1
$10
$100
$1,000
0.1100 10 1Vertical Accuracy (m) RMS
SPOT Satellite
Satellite Stereo SAR
LIDAR
Airborne InSAR
Aerial Photography
High Resolution EOS Plan of China
可见光 红外 多 / 高光谱 紫外 微波
HREOS
Multiple platforms
Multiple sensors
Multiple applications
Resource and environmentAgriculture and forestRegional planningPublic security and emergency response
space born>100km
near space20-100km
airborne<20km
激光
Different techniques for different sources
Field surveying by using total station theodolite and GPS for direct measurement from terrain surfaces
Cartographic digitization by using existing topographic maps and digitisers
Photogrammetry by using stereo-pairs of aerial (or space) images and photogrammetric instruments
Laser scanning: actively providing its own illumination in the form of lasers
SAR: radargrammetry 和 interferometry, actively providing its own illumination in the form of microwaves
From terrain surface
The continents occupy 29.2% of the earth’s surface. Relief varies from place to place, and is covered by natural and cultural features, apart from water
具体采用何种数据源和相应的生产工艺一方面取决于这些源数据的可获得性,另一方面也取决于 DEM 的分辨率、精度要求、数据量大小和技术条件等
From aerial and space images
航空影像一直是地形图测绘和更新最有效也是最主要的数据源 近年来出现的高分辨率遥感图像如 1-m 分辨率的 IKONOS 图像被认为是快速获取高精度、高分辨率 DEM 最有希望的数据源
Aerial photographs can be classified into different types based on different criteria:
Based on colour: colour (true or false) and monochromatic photographs
Based on the attitude of photography: vertical (i.e. main optical axis vertical), tilted(3), and oblique (>3) photographs. Commonly used aerial photographs are tilted photograph
Based on angular field of view: normal, wide angle and super wide angle photography
From aerial and space images
H
fAerial photo (negative)
Aerial photo (positive)
Perspective centre (lens)
Main optical axis
Aerial camera and aerial photography
(a) An aerial Camera (b) Geometry of aerial photography
the scale of the aerial photograph: DEM 的精度可以达到航高的 0.012%
Form in analogue form – recorded on films;and in digital form – scanned/CCD (charge-
coupled device) camera
Acquisition被动式,记录地面反射的电磁辐射。一般图象主动式,发射并接受电磁波。如雷达图象
From existing topographic maps 几乎世界上所有的国家都拥有地形图,这些地形图是 DEM 的另一主要数据源 这些数据源可能由于地形图覆盖范围不够或因地图高程数据的质量不高和等高线信息的不足而比较欠缺。比如在中国的西部这些数据往往不满足现势性要求
A topographic map
From existing topographic maps
在覆盖全国范围的地形图中,比例尺最大的称之为基本比例尺。基本地形图的比例尺在不同国家可能有所不同: 中国 英国 美国
1:50 000 1:10 000 1:24 000 不同比例尺的地形图具有不同的等高距。等高线的密度及其本身的精度决定了地形表达的可信度
topographic maps the metric quality contour map density of contour lines and the
accuracy of the contour lines themselves
不同比例尺的地形图和它们的地形综合特性
地形图比例尺与等高距的关系
地形图 比例尺 特征大比例尺地形图 >1:10,000 综合程度很低,较真实地反映地形中比例尺地形图 1:20,000---1:75,000 作了一定程度的综合,近似地反映地形小比例尺地形图 <1:100,000 综合程度很高,仅反映地形的大致特征
地形图的比例尺 等高距 1 : 200 , 000 25—100 米 1 : 100 , 000 10—40 米 1 : 50 , 000 10—20 米 1 : 25 , 000 5—20 米 1 : 10 , 000 2.5—10 米
Map scales and commonly used contour accuracy
In general, it is expected that the height accuracy of any point interpolated from contour lines will be about to 1/2 to 1/3 of the contour interval (CI)
3.2 Photogrammetry
The word photogrammetry comes from Greek words photos (meaning “light”), gramma (meaning that which is drawn or written) and metron (meaning “to measure”). It originally signified measuring graphically by means of light
Photogrammetry and Remote Sensing is the art, science, and technologyof obtaining reliable information from noncontact imaging and other sensor systems about the Earth and its environment, and other physical objects and processes through recording, measuring, analyzing and representation
http://www.isprs.org/isprs.html
The development of Photogrammetry
Photogrammetry has undergone four stages of development, each of these cycles are approximately 50 years long:
Plane table photogrammetry 1850 ~ 1900 Analog photogrammetry 1900 ~ 1960 Analytical photogrammetry 1960 ~ present Digital Photogrammetry 1990 ~ present
In 1849, A. Laussedat, an officer in the Engineering Corps of the French Army, is regarded by many as the “father of photogrammetry”
(a) Optical plotter (b) Optical-mechanical plotter
(c) Analytical plotter
(d) Digital photogrammetric workstation
摄影测量四个阶段的特性 模拟摄影测量 数值摄影测量 解析摄影测量 数字摄影测量
输入部分(影像) 模拟 模拟 模拟 数字模型部分 模拟 模拟 解析 解析输出部分 模拟 数字 数字 数字
困难度 3 2 1 0灵活度 0 1 2 3
摄影测量的基本原理 用立体像对来恢复三维物体的原始形状即形成所谓的立体模型,然后在立体模型上量测物体的三维空间坐标以代替野外的量测在航空摄影时,一般来说在飞行方向上的重叠度为 60% ,而航线间的重叠度为 30%
旁向重叠 航向重叠
To measure the 3-D coordinates of the objects on the stereo model
3D modelTwo
overlapping photographs
立体坐标量测仪
S1 S2
a’
A
Z
XY
a
)()()()()()()()()()()()(
333
222
333
111
SASASA
SASASA
SASASA
SASASA
ZZcYYbXXaZZcYYbXXa
fy
ZZcYYbXXaZZcYYbXXa
fx
共线方程式
空间交会spatial intersection
In the mathematical expression,XYZ is a geodesic coordinate system; and (i=1,2,3) are the functions of the 三个角方位元素 (φ, ω, κ) :
coscoscossincossinsinsinsincoscossin
sincoscos
sincoscossin
cossinsinsincossinsinsincoscos
3
3
3
2
2
2
1
1
1
cbacbacba
About the mathematical expression
Basic orientations
Interior orientationusing fiducial marks’ image coordinates to unify the image coordinate system
Relative orientation to restore the stereo model by removing the Y parallax using
at least 6 points’ observations
Absolute orientation to scale and orient the stereo model based on the GCP 地面控
制点。实时摄影测量的基本前提就是自动定向
3.3 Radargrammetry and SAR Interferometry
Radargrammetry acquires DTM data through the measurement of parallax (视差)
InSAR acquires DTM data through the determination of phase shifts between two echoes (两个回波的相位差)
反射波
发射波
天线一种全天时、全天候数据获取手段
方位
斜距向
Pixel
iebaiba 22
InSAR 数据处理的特殊性
SAR 影像象素的复数表
经过预处理后,雷达影像的每一像素不仅包含灰度值,而且还包含与雷达斜距 ( 一般取样到垂直于平台飞行方向的斜距上 ) 有关的相位值,这两个信息分量用一个复数来表达
Airborne laser scanning system
a laser range finder (LRF) a computer system to
control the on-line data acquisition
a storage medium a scanner, and a GPS/INS system for
determining the position and orientation of the system
From laser point cloud to DTM
The process of acquiring ALS data: 数据过滤 --noise, outliers or gross errors 分类 --buildings or vegetation 三维重建 激光扫描数据与影像数据的融合
Accuracy: height accuracy is in the range of 10-60 cm planimetric accuracy is 0.1-3m
3.5 Cartographic digitisation
Automated
Manual
Line-following
Scanning
Manual line following
Automated line following
Manual scanning
Automated scanning
数字化后通常还要进行表面建模处理
Differential GPS and its service
constantly compare the real position with the position given by the GPS system, use this error-information to improve GPS performance in a wide range (up to hundreds of kilometers) around the base station
Accuracy: 1-10mmSpeed:1-5 secRange: 20-150KM
市话网
市话网
市话网
市话网
市话网
深圳市连续运行卫星定位导航服务系统结构及通信网络示意图
市电信局
监控分析中心卫星定位信号发射台
FM电台
基准站1
基准站2
基准站3
基准站4
基准站5进入移动
电话系统
用户
用户
全向天线定向天线Modem
Principles of traditional surveying techniques through the measurement of distances and/or angles by theodolites and computerised total stations
D D1 D1
1 2
P P
A A B
(a) From a known point A to determine the position of P
(b) From 2 known points A and B to determine the position of P
3.7 A comparison between DTM data from different sources
获取方式 DEM 的精度 速度 成本 更新程度 应用范围地面测量 非常高( cm ) 耗时 很高 很困难 小范围区域,特别的工程项目摄影测量 比较高( cm-m ) 比较快 比较高 周期性 大的工程项目,国家范围的数据收集立体遥感( SPOT)
低 很快 低 很容易 国家范围乃至全球范围内的数据收集GPS 比较高( cm-m ) 很快 比较高 容易 小范围,特别的项目
地形图手扶跟踪数字化 比较低0.2-0.4mm
比较耗时 低 周期性
国家范围内以及军事上的数据采集,中小比例尺地形图的数据获取地形图扫描 比较低0.1-0.3mm
非常快 比较低激光扫描、干涉雷达 非常高 (cm) 很快 非常高 容易 高分辨率、各种范围
性能 卫星影像 航空影像 地面影像 航空点云 地面点云准确性 低 一般 /高 高 高 高分辨率 低 一般 /高 高 一般 高周期 快速 一般 低 一般 高成本 低 一般 高 高 高纹理 低 一般 高 无 无
三维空间数据获取方法比较