多影像空三平差辅助下的车载全景相机严密标定方法

针对目前全景相机标定方法的研究现状,提出了一种多影像光束法空三平差辅助下的全景相机内参数严密标定方法。首先建立全景相机标定场,对组成全景相机的每台单相机的内参数进行标定;然后按照预先设计好的摄影参数,旋转摄影获取全景相机在标定场中多个不同摄影方向的影像,利用其中一个摄站的标定影像和物方控制点通过空间后方交会的方法解算单相机之间的初始相对方位元素,即粗标定;最后将所有摄站的标定影像构建区域网并进行光束法空三平差,获取精确的全景相机参数,即严密标定。试验表明,文中提出的全景相机标定方法可以提高标定结果的精度和可靠性,为全景影像的拼接、量测及真彩点云的生成等后续研究和应用奠定可靠的基础。     

附加约束条件的光束法区域网平差在四拼数码航空相机平台检校中的应用

介绍了针对四拼数码航空相机的附加约束条件光束法区域网平差原理,包括计算四拼相机外方位元素,并同时计算四台子相机的相对位置关系,获取四拼相机平台检校参数。实验结果表明采用这种方法计算出来的平台检校参数精度高,生成的虚拟影像拼接效果好,测图精度满足大中比例尺地形图规范要求。     

多镜头组合式相机的全景SLAM

同步定位与地图构建(simultaneous localization and mapping,SLAM)是摄影测量、计算机视觉和机器人学的研究热点,并广泛应用于移动测图系统、机器人、无人驾驶车等。本文提出一种针对多镜头组合式全景相机的基于特征的SLAM解决方案。首先,本文建立了鱼眼相机的高精度检校模型,以保证鱼眼相机与全景相机之间的高精度坐标转换;然后,将多镜头组合式全景成像模型嵌入SLAM的初始化、局部地图生成、关键帧选取、图优化等各个流程中。此外,考虑全景相机变形大、基线长的不利因素,本文在特征匹配、平差、特征点跟踪等SLAM的各个步骤都进行了针对性改进。本文在两套车载全景数据集共8000余张全景影像上进行试验。结果表明,本文所提出的全景SLAM很好地实现了全景相机的自动定位与地图构建功能,并达到了接近GPS参考的极高定位精度而无须借助GPS/IMU组合导航系统。相对于主流的基于平面相机的各类SLAM系统,如Mono-SLAM、Stereo-SLAM以及RGB-DSLAM,本文提出的全景SLAM可作为良好的补充,并为GPS信号失锁时的传感器定位提供廉价的自动解决方案。     

资源一号02C卫星全色相机在轨几何定标方法

为提高资源一号02C卫星全色影像几何精度,首先从其严格几何成像模型出发,对成像过程中的几何误差来源及其特性进行分析,在此基础上构建资源一号02C卫星全色相机的在轨几何定标模型;然后,将待定标参数分为内外定标参数,采用分步迭代策略进行解算;最后,基于本文的定标模型及解算方法,利用嵩山定标场提供的高精度参考数据对其进行了在轨几何定标实验。实验结果表明,本文的定标模型及解算方法合理有效,能显著提高资源一号02C卫星全色影像的无控定位精度和有控定位精度;同时,内定标精度优于0.3个像元。     

BUNDLE TRIANGULATION IN ARCHITECTURAL PHOTOGRAMMETRY: THE BASILICA OF SAN FRANCESCO IN SIENA

Bundle triangulation is an efficient tool for spatial point determination in architectural photogrammetry. All the information available in image and object space may be introduced in a combined adjustment yielding high precision and reliability. Camera calibration performed simultaneously with the object restitution process enables the application of convenient and flexible imaging systems based on professional photographic technology. Thus the survey of monuments can be carried out rapidly with a minimum of personnel and equipment. The photogrammetric recording of the basilica of San Francesco in Siena is presented as an example of the application of this survey procedure. The field work was accomplished in a few days. The equipment used consisted of a partial metric camera, an engineering theodolite and a tape. The bundle adjustment results gave spatial object co-ordinates with a r.m.s.e. of ± 15 mm for a point.     

Evaluation of the geometric stability and the accuracy potential of digital cameras — Comparing mechanical stabilisation versus parameterisation

Recent tests on the geometric stability of several digital cameras that were not designed for photogrammetric applications have shown that the accomplished accuracies in object space are either limited or that the accuracy potential is not exploited to the fullest extent. A total of 72 calibrations were calculated with four different software products for eleven digital camera models with different hardware setups, some with mechanical fixation of one or more parts. The calibration procedure was chosen in accord to a German guideline for evaluation of optical 3D measuring systems [VDI/VDE, VDI/VDE 2634 Part 1, 2002. Optical 3D Measuring Systems–Imaging Systems with Point-by-point Probing. Beuth Verlag, Berlin]. All images were taken with ringflashes which was considered a standard method for close-range photogrammetry. In cases where the flash was mounted to the lens, the force exerted on the lens tube and the camera mount greatly reduced the accomplished accuracy. Mounting the ringflash to the camera instead resulted in a large improvement of accuracy in object space. For standard calibration best accuracies in object space were accomplished with a Canon EOS 5D and a 35 mm Canon lens where the focusing tube was fixed with epoxy (47  μm maximum absolute length measurement error in object space). The fixation of the Canon lens was fairly easy and inexpensive resulting in a sevenfold increase in accuracy compared with the same lens type without modification. A similar accuracy was accomplished with a Nikon D3 when mounting the ringflash to the camera instead of the lens (52  μm maximum absolute length measurement error in object space). Parameterisation of geometric instabilities by introduction of an image variant interior orientation in the calibration process improved results for most cameras. In this case, a modified Alpa 12 WA yielded the best results (29  μm maximum absolute length measurement error in object space). Extending the parameter model with FiBun software to model not only an image variant interior orientation, but also deformations in the sensor domain of the cameras, showed significant improvements only for a small group of cameras. The Nikon D3 camera yielded the best overall accuracy (25  μm maximum absolute length measurement error in object space) with this calibration procedure indicating at the same time the presence of image invariant error in the sensor domain. Overall, calibration results showed that digital cameras can be applied for an accurate photogrammetric survey and that only a little effort was sufficient to greatly improve the accuracy potential of digital cameras.     

SIMULTANEOUS CALIBRATION OF A PHOTOGRAMMETRIC STEREOPAIR

Procedures for the calibration of a stereopair simultaneously with a bundle adjustment are presented. Distances and directions in object space are used as additional observations. The analytical simultaneous calibration of a photogrammetric camera is essential when instrument methods do not determine the precalibrated parameters of interior orientation with sufficient accuracy.     

一种无需控制信息的智能手机自检校方法

传统的相机检校方法受限于高精度的三维检校场或已知空间结构的检校模板,针对这个问题,在分析智能手机成像特征的基础上,提出一种无需控制信息的相机检校方法。该方法主要包括两个步骤:首先按3×3模式采集影像数据,选取基准影像,分别与其他影像进行相对定向以构建单元模型,通过比例系数进行模型连接后建立自由网模型,将所有摄站点、物方点坐标纳入到统一的基准影像坐标系中;然后以选择的基准影像为参考,并考虑附加参数模型,进行自检校光束法自由网平差,解算其余影像相对于基准影像的方位元素以及附加参数,从而完成相机的检校。实验结果表明,该检校方法是有效的,可显著提高测量的精度。     

Using horizontal and vertical building structure to constrain indirect sensor orientation

This paper presents a method to integrate linear horizontal, vertical and right-angled scene structures into the bundle adjustment of image sequences. An increasing number of airborne image acquisition systems is available and equipped with non-metric small- or medium-frame cameras and no or insufficiently accurate INS devices. In cases where the data is to be used for the production of geo-spatial data, where a certain accuracy and precision is required, an indirect sensor orientation, possibly including self-calibration, needs to be performed. The idea which led to the presented approach is to reduce the number of GCPs necessary for this task by applying the mentioned scene structures. The method directly uses the linear structures, visible at man-made objects as fictive observations within the adjustment, while self-calibration of intrinsic camera parameters and lens distortion is included as well.Experiments with two datasets demonstrate that, through this method, only limited GCP information is required to obtain satisfactory results. In fact, in one experiment using oblique images, several scene constraints were provided and only the datum was defined by ground control. The residuals at check points from this setup were similar to the traditional case where several well-distributed GCPs were available in the scene. In the second experiment the ability of this approach to support the bundle adjustment was shown for a UAV dataset. Although no GCP and camera calibration information was available, the visual inspection of adjusted object points and the residuals at horizontal structures confirmed the ability of the method to align an image block with the structure, as embodied in the defined scene constraints. Despite the convincing outcome of the experiments, it needs to be mentioned that some manual work is still involved in defining the constraints. In future work the issue of automation will be addressed.     

A multi-sensor approach to creating accurate virtual environments

Creating virtual environment models often requires geometric data from range sensors as well as photometric data from CCD cameras. The model must be geometrically correct, visually realistic, and small enough in size to allow real-time rendering. We present an approach based on 3D range sensor data, multiple CCD cameras, and a colour high-resolution digital still camera. The multiple CCD cameras provide images for a photogrammetric bundle adjustment with constraints. The results of the bundle adjustments are used to register the 3D images from the range sensor in one coordinate system. The images from the high-resolution still camera provide the texture for the final model. The paper describes the system, the techniques for the registration of the 3D images, the building of the efficient geometric model, and the registration and integration of the texture with a simplified geometric model.     

A bundle adjustment approach with inner constraints for the scaled orthographic projection

Bundle adjustment is a method for simultaneously calculating both the interior and exterior orientation parameters of a set of images, and the object-space coordinates of the observed points. In the case of long focal length lenses and narrow field-of-view (FOV) imaging situations, collinearity based (perspective projection) algorithms may result in linear dependencies between parameters that cause solution instability. The use of a scaled orthographic projection model based on linear algebraic formulations was therefore adopted to reduce this risk. Using quaternions, a new mathematical model is derived that includes the partial derivatives as well as the inner constraint equations for a scaled orthographic bundle adjustment. The model was then tested using two image sets of a single, small vessel (about 6 m length) with a cube target of known dimensions at two distinct ranges; perspective solutions were also calculated for comparison. RMS residual errors of 0.74-0.78 pixels associated with the new method compare favorably to a residual error range of 0.59-0.74 pixels using a perspective bundle adjustment of the same target points. Relative precisions (as a ratio of target size) of between 1:1650 and 1:750 have been achieved at ranges of 375 m and 850 m, respectively, given comparisons with the known cube dimensions. A third image dataset consisting of a network of 16 images was solved with a 1:2200 relative precision showing the new method can successfully handle high redundancy. For the experiments that were conducted, the new method was found to produce less precise results than the perspective bundle solution for a FOV of 0.50-0.65° where the object fills 5-8% of the image. However, it was found to match the precision of the perspective model (with an uncalibrated camera) for a FOV of 0.20-0.30° where the object of interest fills only 1-2% of the full image.     

一种图像自动拼接方法的研究

以关键帧作为待拼接图像,为了减少图像间的扭曲和变形,保证图像整体关系的正确性,减少误差的累积传播,得到最佳的拼接结果,本文采用三种技术来提高图像自动拼接的精度。首先,通过摄像机标定实现关键帧的矫正;其次,采用基于Harris和SURF算法完成特征点的匹配;最后,在特征匹配的基础上进行光束法平差得到高精度的图像参数。实验结果表明,此方法稳定可靠,拼接精度高。     

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。     

基于单位四元数的机载三线阵影像光束法平差

为克服欧拉角在空间方位的描述和插值中的局限性,采用单位四元数来描述相机的姿态,推导了四元数描述的共线条件方程。在此基础上,提出了将四元数球面线性插值(Slerp)引入到三线阵影像定向片法平差的思想,通过利用Slerp公式进行相机姿态的匀速插值,建立了基于单位四元数的三线阵影像平差的数学模型并进行了线性化。两套ADS40数据的试验结果表明,在区域四角布设平高控制点的情况下,基于Slerp模型的定向片光束法平差在平面和高程方向均可取得优于1个地面像元(GSD)的定位精度,是三线阵相机检校和空中三角测量较理想的技术手段。     

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.     

Bundle Adjustment with Self–Calibration Using Straight Lines

Increased use of digital imagery has facilitated the opportunity to use features, in addition to points, in photogrammetric applications. Straight lines are often present in object space, and prior research has focused on incorporating straight–line constraints into bundle adjustment for frame imagery. In the research reported in this paper, object–space straight lines are used in a bundle adjustment with self–calibration. The perspective projection of straight lines in the object space produces straight lines in the image space in the absence of distortions. Any deviations from straightness in the image space are attributed to various distortion sources, such as radial and decentric lens distortions. Before incorporating straight lines into a bundle adjustment with self–calibration, the representation and perspective transformation of straight lines between image space and object space should be addressed. In this investigation, images of straight lines are represented as a sequence of points along the image line. Also, two points along the object–space straight line are used to represent that line. The perspective relationship between image– and object–space lines is incorporated in a mathematical constraint. The underlying principle in this constraint is that the vector from the perspective centre to an image point on a straight–line feature lies on the plane defined by the perspective centre and the two object points defining the straight line. This constraint has been embedded in a software application for bundle adjustment with self–calibration that can incorporate point as well as straight–line features. Experiments with simulated and real data have proved the feasibility and the efficiency of the algorithm proposed.     

多相机数码影像光束法解算及精度分析

光束法算法通常用于解决同一相机影像的平差解算问题,文中探讨多相机数码影像的光束法解算方法,理论研究与实验分析相结合,研究建立多相机影像光束法的平差模型,并在相同条件下与单相机光束法解算结果相比较。结果表明,多相机数码影像光束法严密平差可解,且分别在不同的控制条件下与单相机光束法解算精度相当。     

粒子加速器中高精度丝线绝对位置测量技术研究

粒子加速器中采用振动线技术进行共架单元上多块磁铁的高精度预准直,需要将振动线代表的磁中心引出进行共架单元之间的相对准直。为了获取以振动线为代表的丝线高精度空间绝对位置,本文对采用近景摄影测量技术进行点、线位置求解的方法进行了研究。利用单相机多站位的方法进行拍摄,通过标定板提供的高精度控制点坐标,采用自标定光束法平差对相机进行标定,并提出将空间直线离散成空间2点进行直线整体精确求解。对标定板上由2点组成的模拟直线进行测量验证,并与标定板提供的理论值进行对比,结果显示空间直线位置获取精度优于5 μm。这表明了本文理论和方法的正确性,为进一步研究丝线高精度空间绝对位置测量打下了基础。     

Nikon D1X相机检校

本文采用空间后方交会方法对Nikon D1X数码相机(NIKKOR 17镜头)在室内检校场实施检校。通过分析检校结果的精度,并经多片空间前方交会方法进一步验证检校参数的可靠性,表明多片空间后方交会是一种较为可靠的数码相机检校方法。