HIGH PRECISION CCD CALIBRATION AND ITS APPLICATIONS

ABSTRACT

With the help of CCD images, the realization of high precision positioning and measurement has become the basic standard for machine vision and real time photogrammetry systems. However, deformation and other sorts of degradation occurring during transmission are major limiting factors of the precision attainable with most current CCD cameras and frame grabbers. So a precise radiometric and geometric transmission of images from CCD sensor to memory is a fundamental aspect of CCD camera calibration. The geometric calibration system, which uses some image processing algorithms of the CCD camera based on the researched and developed system is discussed. The reliability and validity are also discussed. The experimental results for the calibration of the CCD array will be taken as an important quality index for CCD evaluation.     

一种非共线TDI CCD成像数据内视场拼接方法

星载非共线TDI CCD成像数据的高质量内视场拼接是保证影像后续处理和应用的基础。本文提出了一种非共线TDI CCD成像数据内视场拼接方法,该方法基于物方投影面和相机的传感器几何模型,建立了从拼接影像像点到原始影像像点的坐标转换关系,进而采用间接法影像纠正的方式对原始影像进行重采样生成拼接影像。本文在描述非共线TDI CCD严格成像几何模型之后,详细叙述了方法的基本原理、潜在的误差来源以及方法的实现流程,并通过ZY-1 02C卫星的高分辨率（HR）相机成像数据进行了试验验证,对拼接精度的分析与评价证明了方法的可行性。     

CCD摄像机面阵几何检校的自动化方法

利用CCD 摄像机实现目标点的高精度定位和量测是计算机机器视觉和实时摄影测量系统的基本手段。而CCD 摄像机获取的目标影像在传输的过程中受到几何精度的限制。所以,目标影像从CCD 传感器到存储器的高精度的辐射和几何传输是CCD 摄像机检校的基本问题。作者在一新研制的解析测图仪上,设计了一套CCD 摄像机自动检校的软件系统。本文对该软件系统进行了介绍,并通过检校试验,证明了其可靠性和实用性。     

HIGH PRECISION CCD CALIBRATION AND ITS APPLICATIONS

With the help of CCD images,the realization of high precision po-sitioning and measurement has become the basic standard for machine vision andreal time photogrammetry systems.However,deformation and other sorts ofdegradation occurring during transmission are major limiting factors of the preci-sion attainable with most current CCD cameras and frame grabbers.So a preciseradiometric and geometric transmission of images from CCD sensor to memory is afundamental aspect of CCD camera calibration.The geometric calibration system,which uses some image processing algorithms of the CCD camera based on the re-searched and developed system is discussed.The reliability and validity are alsodiscussed.The experimental results for the calibration of the CCD array will betaken as an important quality index for CCD evaluation.     

Sensor modeling,self-calibration and accuracy testing of panoramic cameras and laser scanners

Terrestrial Linear Array CCD-based panoramic cameras have been used for purely imaging purposes, but they also have a high potential for use in high accuracy measurement applications. The imaging geometry and the high information content of those images make them suitable candidates for quantitative image analysis. For that a particular sensor model has to be established and the inherent accuracy potential has to be investigated. We developed a sensor model for terrestrial Linear Array-based panoramic cameras by means of a modified bundle adjustment with additional parameters, which models substantial deviations of a real camera from the ideal one. We used 3D straight-line information in addition to tie points to conduct a full calibration and orientation without control point information. Due to the similarity of the operation of laser scanners to panoramic cameras the sensor model of the panoramic cameras was extended for the self-calibration of laser scanners. We present the joint sensor model for panoramic cameras and laser scanners and the results of self-calibration, which indicate a subpixel accuracy level for such highly dynamic systems. Finally we demonstrate the systems’ accuracy of two typical panoramic cameras in 3D point positioning, using both a minimal number of control points and a free network adjustment. With these new panoramic imaging devices we have additional powerful sensors for image recording and efficient 3D object modeling.     

基于单CCD相机和经纬仪的几何测量方法研究

传统视觉测量系统需要双CCD相机同时拍摄两幅不同角度的数字图像,成本昂贵且难以确定两CCD相机问的空间相对位置。为此,建立一种结合CCD相机的摄像功能和经纬仪高精度测角功能的视觉测量系统。基于该系统提出一种用单CCD相机实现双目视觉原理的数学模型。实验结果证明系统与数学模型的可行性。     

结构光系统结合数码相机的小物体高质量纹理重建

针对双鸟饕餮纹夔神鼍鼓等小文物或其他小型物体,提出了基于结构光扫描系统结合普通高分辨率单反数码相机的纹理重建方法。该方法具有自动化程度高、效率和质量高的特点,其中主要解决了单张高分辨率影像与物体几何模型的自动配准,以及配准后从多张影像生成无缝纹理模型的问题。实验证明了本文方法的可行性和有效性。     

SWDC-5倾斜像片定位定姿方法研究

基于SWDC-5航摄仪获取的数据,探讨倾斜像片定位定姿的方法,通过建立POS、下视相机、斜视相机间的相对关系模型,给出POS辅助SWDC-5倾斜像片直接地理定位技术流程。通过实际航飞数据计算得到的倾斜像片外方位元素可用于三维房屋模型纹理映射,经试验验证该方法正确、可行。     

Geometric in-flight calibration of the stereoscopic line-CCD scanner MOMS-2P

This paper describes the geometric in-flight calibration of the Modular Optoelectronic Multispectral Scanner MOMS-2P, which has collected digital multispectral and threefold along-track stereoscopic imagery of the earth's surface from the PRIRODA module of the Russian space station MIR from October 1996 to August 1999. The goal is the verification and, if necessary, the update of the calibration data, which were estimated from the geometric laboratory calibration. The paper is subdivided into two parts, describing two different procedures of geometric in-flight calibration. The first method is based on DLR matching software and is restricted to nadir looking channels, which are read out simultaneously. From a high number of individual point matches between the images of the same area taken by the different CCD arrays, the most reliable ones are selected and used to calculate shifts with components in and across flight direction between the CCD arrays. These actual shifts are compared to the nominal shifts, derived from the results of the laboratory calibration, and parameters of the valid camera model are estimated from both data sets by least squares adjustment. A special case of band-to-band registration are the two optically combined CCD-arrays of the nadir high-resolution channel. They are read out simultaneously with a nominal 10 pixel overlap in stereoscopic imaging mode A. The DLR matching software is applied to calculate the displacement vector between the two CCD-arrays. The second method is based on combined photogrammetric bundle adjustment using an adapted functional model for the reconstruction of the interior orientation. It requires precise and reliable ground control information as well as navigation data of the navigation-package MOMS-NAV. Nine contiguous image scenes of MOMS-2P data-take T083C building an about 550-km-long strip over southern Germany and Austria taken in March 1997 were evaluated. From both procedures calibration data are estimated, which are presented and compared to the lab-calibration results.     

Principal Point Behaviour and Calibration Parameter Models for Kodak DCS Cameras

Digital still cameras have been widely adopted for close range photogrammetry and machine vision applications. Due to the advantages of onboard storage of digital images, portability and rapid data processing, digital still cameras are rapidly becoming standard equipment for measurement tasks such as industrial metrology and heritage recording. As for any metric application, the accuracy of the derived object data is dependent, amongst many other factors, on the accuracy of the camera calibration. For the vast majority of photogrammetric applications, use of the simple case of a block invariant calibration model comprising the primary physical parameters, including the principal point position, is sufficient. However, cameras designed for photojournalism and domestic use, such as the Kodak DCS420 and 460 cameras, are well known for their calibration instability because the design is based on a 35 mm SLR camera body. In particular, previous research has shown that the principal point location is prone to movement during normal handling of the camera, due to the mounting mechanism of the CCD array. This paper reports on an investigation of the physical behaviour of the principal point location and compares different calibration parameter models for the Kodak DCS420 and DCS460 digital still cameras.     

基于华浩超算平台几何精校正模块的波段配准研究

KOMPSAT3(阿里郎三号)卫星携带高分辨率0.7 m全色和2.8 m多光谱有效载荷,回访周期短,覆盖范围广,得到了广泛的应用。但由于受太阳辐射、大气干扰、云折射等物理因素的影响,造成波段之间在局部区域图像上发生非线性几何畸变,导致多光谱假彩色合成数据产生重叠现象,严重影响多光谱数据质量。本文针对在极端条件下产生的图像局部非线性几何畸变现象,探索国内外各种波段间配准方法,研究发现基于华浩超算平台的几何精校正算法能很好地达到波段间配准效果,消除了多光谱假彩色合成数据的影像重叠现象。     

基于ICP方法缺乏纹理物体三维曲面模型的匹配

对缺乏纹理物体建立三维模型,关键的难度在于缺乏特征点和点的坐标获得。本文采用ICP算法来对物体进行匹配,当特征点不足时,ICP算法是一个很适用的匹配方法,只需要对物体的给定点寻找最近点。为了计算目标点的坐标,利用投影器投射清晰稳定的纹理到缺乏纹理物体的表面,然后CCD相机对物体进行拍摄。通过线检测和空间前方交会解算出物体部分模型表面的空间点;并使用无需控制点的ICP方法对相互重叠的部分模型进行匹配,从而完成物体的三维重建。实验证明ICP方法对缺乏纹理物体的三维曲面匹配有效。     

A comparison of dense matching algorithms for scaled surface reconstruction using stereo camera rigs

Photogrammetric methods for dense 3D surface reconstruction are increasingly available to both professional and amateur users who have requirements that span a wide variety of applications. One of the key concerns in choosing an appropriate method is to understand the achievable accuracy and how choices made within the workflow can alter that outcome. In this paper we consider accuracy in two components: the ability to generate a correctly scaled 3D model; and the ability to automatically deliver a high quality data set that provides good agreement to a reference surface. The determination of scale information is particularly important, since a network of images usually only provides angle measurements and thus leads to unscaled geometry. A solution is the introduction of known distances in object space, such as base lines between camera stations or distances between control points. In order to avoid using known object distances, the method presented in this paper exploits a calibrated stereo camera utilizing the calibrated base line information from the camera pair as an observational based geometric constraint. The method provides distance information throughout the object volume by orbiting the object.In order to test the performance of this approach, four topical surface matching methods have been investigated to determine their ability to produce accurate, dense point clouds. The methods include two versions of Semi-Global Matching as well as MicMac and Patch-based Multi-View Stereo (PMVS). These methods are implemented on a set of stereo images captured from four carefully selected objects by using (1) an off-the-shelf low cost 3D camera and (2) a pair of Nikon D700 DSLR cameras rigidly mounted in close proximity to each other. Inter-comparisons demonstrate the subtle differences between each of these permutations. The point clouds are also compared to a dataset obtained with a Nikon MMD laser scanner. Finally, the established process of achieving accurate point clouds from images and known object space distances are compared with the presented strategies.Results from the matching demonstrate that if a good imaging network is provided, using a stereo camera and bundle adjustment with geometric constraints can effectively resolve the scale. Among the strategies for dense 3D reconstruction, using the presented method for solving the scale problem and PMVS on the images captured with two DSLR cameras resulted in a dense point cloud as accurate as the Nikon laser scanner dataset.     

由小面阵CCD组合构成宽角航空相机

本文研究由多台小面阵CCD相机构建组合式宽角航空相机的新方法———包括由3台或4台相机组合构建的多相机系统结构,由其分离的各影像转换成等效大影像的数学表达;利用室外和室内近景相机检校场对组合相机系统进行高精度检校的内容、解算方法和检校结果;最后给出了以3相机组合系统装备无人驾驶飞行器(UAV II)进行低空摄影的影像成果。     

Context-based automatic reconstruction and texturing of 3D urban terrain for quick-response tasks

Highly detailed 3D urban terrain models are the base for quick response tasks with indispensable human participation, e.g., disaster management. Thus, it is important to automate and accelerate the process of urban terrain modeling from sensor data such that the resulting 3D model is semantic, compact, recognizable, and easily usable for training and simulation purposes. To provide essential geometric attributes, buildings and trees must be identified among elevated objects in digital surface models. After building ground-plan estimation and roof details analysis, images from oblique airborne imagery are used to cover building faces with up-to-date texture thus achieving a better recognizability of the model. The three steps of the texturing procedure are sensor pose estimation, assessment of polygons projected into the images, and texture synthesis. Free geographic data, providing additional information about streets, forest areas, and other topographic object types, suppress false alarms and enrich the reconstruction results.     

An automated seamless mosaicing system of multi-charge coupled devices of panchromatic data

Panchromatic data of pixel resolution 5.8 m obtained from IRS-1C and IRS-1D satellites proved to be very useful for mapping purposes. One of the popular data product is the 70 km swath mosaic which is covered by a combination of 3 CCD line sensors, each with 4096 pixels. Each CCD-line sensor with different imaging times causes geometric problems of mosaicing three strips data together. In this paper, we propose the details of the design elements of system that caters to the need for accurate and automatic multi strip image registration without any second resampling of the data. The systematic geometric correction grid mapping is improved to facilitate accurate mosaicing by automatic image registration task that makes use of the overlap data within image strips and image registration is achieved up to sub-pixel level.     

高分辨率遥感卫星传感器严格成像模型的建立及验证

本文对高分辨率遥感卫星传感器严格成像模型进行了深入研究。分析了星载线阵CCD传感器严格成像模型的一般建立方法与过程,针对SPOT 5 HRS/HRG、ALOS PRISM、资源三号TLC等典型的高分辨率遥感卫星传感器特点,分别给出了3种改化的严格成像模型;设计了基于光束法区域网平差的模型验证方法。利用登封遥感实验场区域的3种卫星影像及相关辅助数据,对严格成像模型的正确性进行了验证。结果表明3种改化模型可有效实现卫星影像的平差定位。     

CE-1立体相机成像几何模型研究

传感器成像几何模型是摄影测量数据处理的关键问题.本文分析了CE-1立体相机成像几何原理、阐述了立体相机内定向以及根据探月卫星辅助数据计算外定向参数的原理和方法;提出一种快速反投影变换算法,建立了 CE-1立体相机成像几何模型.通过对CE-1三线阵影像、激光高度计数据的配准买验,验证了本文的有效性本文立体相机成像几何模型...     

国产机载大视场三线阵CCD相机GNSS偏心矢量和IMU视轴偏心角标定技术

针对国内首台自主研制的机载三线阵CCD相机（以下简称GFXJ）,开展了国产GFXJ的GNSS偏心矢量和IMU视轴偏心角标定技术研究工作。首先介绍了GFXJ相机的成像特点,然后分析建立了GFXJ的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型,并提出了GNSS偏心矢量和视轴偏心角循环两步法标定方案,最后在国家嵩山遥感综合实验场获得了多次飞行试验数据。通过进行区域网平差和标定处理,验证了本文建立的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型的正确性和有效性,证实了本文提出的循环两步法标定方案可靠、可行,可显著提升GFXJ的几何定位精度。利用GNSS偏心矢量和IMU视轴偏心角标定值,大幅提高了GFXJ相机的无控定位精度。辅以少量控制点进行区域网平差,GFXJ影像平面定位精度可满足1：1000地形图测图的空中三角测量精度要求,高程精度距离指标要求略有差距。目前该款相机仍在校飞阶段,定型后几何性能有望进一步提高。同时,本文建立的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型及提出的循环两步法标定方案,可为其他机载线阵CCD相机的标定处理提供借鉴。     

Monocular 3D scene reconstruction at absolute scale

In this article we propose a method for combining geometric and real-aperture methods for monocular three-dimensional (3D) reconstruction of static scenes at absolute scale. Our algorithm relies on a sequence of images of the object acquired by a monocular camera of fixed focal setting from different viewpoints. Object features are tracked over a range of distances from the camera with a small depth of field, leading to a varying degree of defocus for each feature. Information on absolute depth is obtained based on a Depth-from-Defocus approach. The parameters of the point spread functions estimated by Depth-from-Defocus are used as a regularisation term for Structure-from-Motion. The reprojection error obtained from bundle adjustment and the absolute depth error obtained from Depth-from-Defocus are simultaneously minimised for all tracked object features. The proposed method yields absolutely scaled 3D coordinates of the scene points without any prior knowledge about scene structure and camera motion. We describe the implementation of the proposed method both as an offline and as an online algorithm. Evaluating the algorithm on real-world data, we demonstrate that it yields typical relative scale errors of a few per cent. We examine the influence of random effects, i.e. the noise of the pixel grey values, and systematic effects, caused by thermal expansion of the optical system or by inclusion of strongly blurred images, on the accuracy of the 3D reconstruction result. Possible applications of our approach are in the field of industrial quality inspection; in particular, it is preferable to stereo cameras in industrial vision systems with space limitations or where strong vibrations occur.