The paper analyses differences between dome and flat port housings used for underwater photogrammetry. The underwater environment negatively affects image quality and 3D reconstructions, but this influence on photogrammetric measurements, so far, has not been addressed properly in the literature. In this work, motivations behind the need for systematic underwater calibrations are provided, then experimental tests using a specifically designed photogrammetric modular test object in laboratory and at sea are reported. The experiments are carried out using a Nikon D750 24 Mpx DSLR camera with a 24 mm f2.8 AF/D lens coupled with a NIMAR NI3D750ZM housing, equipped first with a dome and, successively, with a flat port. To quantify the degradation of image quality, MTF measurements are carried out, then the outcomes of self-calibrating bundle adjustment calibrations are shown and commented. Optical phenomena like field curvature as well as chromatic aberration and astigmatism are analysed and their implications on the degradation of image quality is factored in the bundle adjustment through a different weighting of 2D image observations.
The paper investigates the performances of two portable mobile mapping systems (MMSs), the handheld GeoSLAM ZEB-REVO and Leica Pegasus:Backpack, in two typical user-case scenarios: an indoor two-floors building and an outdoor open city square. The indoor experiment is characterized by smooth and homogenous surfaces and reference measurements are acquired with a time-of-flight (ToF) phase-shift laser scanner. The noise of the two MMSs is estimated through the fitting of geometric primitives on simple constructive elements, such as horizontal and vertical planes and cylindrical columns. Length measurement errors on different distances measured on the acquired point clouds are also reported. The outdoor tests are compared against a MMSs mounted on a car and a robust statistical analysis, entailing the estimation of both standard Gaussian and non-parametric estimators, is presented to assess the accuracy potential of both portable systems.
This paper aims to provide a procedure for improving automated 3D reconstruction methods via vision metrology. The 3D reconstruction problem is generally addressed using two different approaches. On the one hand, vision metrology (VM) systems try to accurately derive 3D coordinates of few sparse object points for industrial measurement and inspection applications; on the other, recent dense image matching (DIM) algorithms are designed to produce dense point clouds for surface representations and analyses. This paper strives to demonstrate a step towards narrowing the gap between traditional VM and DIM approaches. Efforts are therefore intended to (i) test the metric performance of the automated photogrammetric 3D reconstruction procedure, (ii) enhance the accuracy of the final results and (iii) obtain statistical indicators of the quality achieved in the orientation step. VM tools are exploited to integrate their main functionalities (centroid measurement, photogrammetric network adjustment, precision assessment, etc.) into the pipeline of 3D dense reconstruction. Finally, geometric analyses and accuracy evaluations are performed on the raw output of the matching (i.e. the point clouds) by adopting a metrological approach. The latter is based on the use of known geometric shapes and quality parameters derived from VDI/VDE guidelines. Tests are carried out by imaging the calibrated Portable Metric Test Object, designed and built at University College London (UCL), UK. It allows assessment of the performance of the image orientation and matching procedures within a typical industrial scenario, characterised by poor texture and known 3D/2D shapes.
Motion capture (MOCAP) systems are used in many fields of application (e.g., machine vision, navigation, industrial measurements, medicine) for tracking and measuring the 6DOF (Degrees-Of-Freedom) of bodies. A variety of systems has been developed in the commercial, as well as research domain, exploiting different sensors and techniques, among which optical methods, based on multi-epoch photogrammetry, are the most common. The authors have developed an off-line low-cost MOCAP system made up of three consumer-grade video cameras, i.e. a multi-view camera system. The system was employed in two different case studies for measuring the motion of personnel working onboard a fishing boat and of a ship model in a towing tank (or model basin) subjected to different sea conditions. In this contribution, the same three single cameras are separately processed to evaluate the performances of a sequential space resection method for estimated the 6DOF of a rigid body (a ship model during high frequency tests in a model basin). The results from each video camera are compared with the motion estimated using the multi-view approach, with the aim of providing a quantitative assessment of the performances obtainable.
The paper presents a metric investigation of the Fuji FinePix Real 3D W1 stereo photo-camera. The stereo-camera uses a synchronized Twin Lens-CCD System to acquire simultaneously two images using two Fujinon 3x optical zoom lenses arranged in an aluminum die-cast frame integrated in a very compact body. The nominal baseline is 77 mm and the resolution of the each CCD is 10 megapixels. Given the short baseline and the presence of two optical paths, the investigation aims to evaluate the accuracy of the 3D data that can be produced and the stability of the camera. From a photogrammetric point of view, the interest in this camera is its capability to acquire synchronized image pairs that contain important 3D metric information for many close-range applications (human body parts measurement, rapid prototyping, surveying of archeological artifacts, etc.). Calibration values - for the left and right cameras - at different focal lengths, derived with an in-house software application, are reported together with accuracy analyses. The object coordinates obtained from the bundle adjustment computation for each focal length were compared to reference coordinates of a test range by means of a similarity transformation. Additionally, the article reports on the investigation of the asymmetrical relative orientation between the left and right camera.
The article presents an innovative methodology for the 3D surveying and modeling of floating and semi-submerged objects. Photogrammetry is used for surveying both the underwater and emerged parts of the object and the two surveys are combined together by means of special rigid orientation devices. The proposed methodology is firstly applied to a small pleasure boats (approximately 6 meters long) - hence a free floating case - and then to a large shipwreck (almost 300 meters long) interested by a 52 m long leak at the waterline. The article covers the entire workflow, starting from the camera calibration and data acquisition down to the assessment of the achieved accuracy, the realization of the digital 3D model by means of dense image matching procedures as well as deformation analyses and comparison with the craft original plane.
KEYWORDS: Image registration, Image processing, Signal processing, Feature extraction, Digital signal processing, Data modeling, Visualization, 3D modeling, Image resolution, Data acquisition
Thanks to the recent technological advances, a large variety of image data is at our disposal with variable geometric,
radiometric and temporal resolution. In many applications the processing of such images needs high performance
computing techniques in order to deliver timely responses e.g. for rapid decisions or real-time actions. Thus, parallel or
distributed computing methods, Digital Signal Processor (DSP) architectures, Graphical Processing Unit (GPU)
programming and Field-Programmable Gate Array (FPGA) devices have become essential tools for the challenging issue
of processing large amount of geo-data. The article focuses on the processing and registration of large datasets of
terrestrial and aerial images for 3D reconstruction, diagnostic purposes and monitoring of the environment. For the
image alignment procedure, sets of corresponding feature points need to be automatically extracted in order to
successively compute the geometric transformation that aligns the data. The feature extraction and matching are ones of
the most computationally demanding operations in the processing chain thus, a great degree of automation and speed is
mandatory. The details of the implemented operations (named LARES) exploiting parallel architectures and GPU are
thus presented. The innovative aspects of the implementation are (i) the effectiveness on a large variety of unorganized
and complex datasets, (ii) capability to work with high-resolution images and (iii) the speed of the computations.
Examples and comparisons with standard CPU processing are also reported and commented.
In this paper, a technique for the integration of images and point cloud for urban areas classification is pre-
sented. A set of aerial RGB overlapping images are used as input. A photogrammetric Digital Surface Model
(DSM) is firstly generated by using advanced matching techniques. Subsequently, a thematic classification of
the surveyed areas is performed considering simultaneously the surface’s reflectance in the visible spectrum of
the image sequence, the altitude information (provided by the generated DSM) and additional spatial features
(Attribute Profiles). Exploiting the geometrical constraints provided by the collinearity condition and the epipo-
lar geometry between the images, the thematic classification of the land cover can be improved by considering
simultaneously the height information and the reflectance values of the DSM. Examples and comments of the
proposed classification algorithm are given using a set of aerial images over a dense urban area.
3D imaging systems are widely available and used for surveying, modeling and entertainment applications, but clear
statements regarding their characteristics, performances and limitations are still missing. The VDI/VDE and the ASTME57
committees are trying to set some standards but the commercial market is not reacting properly. Since many new
users are approaching these 3D recording methodologies, clear statements and information clarifying if a package or
system satisfies certain requirements before investing are fundamental for those users who are not really familiar with
these technologies. Recently small and portable consumer-grade active sensors came on the market, like TOF rangeimaging
cameras or low-cost triangulation-based range sensor. A quite interesting active system was produced by
PrimeSense and launched on the market thanks to the Microsoft Xbox project with the name of Kinect. The article
reports the geometric investigation of the Kinect active sensors, considering its measurement performances, the accuracy
of the retrieved range data and the possibility to use it for 3D modeling application.
Automatic image orientation of close-range image blocks is becoming a task of increasing importance in the practice of
photogrammetry. Although image orientation procedures based on interactive tie point measurements do not require any
preferential block structure, the use of structured sequences can help to accomplish this task in an automated way.
Automatic orientation of image sequences has been widely investigated in the Computer Vision community. Here the
method is generally named "Structure from Motion" (SfM), or "Structure and Motion". These refer to the simultaneous
estimation of the image orientation parameters and 3D object points of a scene from a set of image correspondences.
Such approaches, that generally disregard camera calibration data, do not ensure an accurate 3D reconstruction, which is
a requirement for photogrammetric projects. The major contribution of SfM is therefore viewed in the photogrammetric
community as a powerful tool to automatically provide a dense set of tie points as well as initial parameters for a final
rigorous bundle adjustment. The paper, after a brief overview of automatic procedures for close-range image sequence
orientation, will show some characteristic examples. Although powerful and reliable image orientation solutions are
nowadays available at research level, there are certain questions that are still open. Thus the paper will also report some
open issues, like the geometric characteristics of the sequences, scene's texture and shape, ground constraints (control
points and/or free-network adjustment), feature matching techniques, outlier rejection and bundle adjustment models.
The extraction of information from image and range data is one of the main research topics. In literature, several papers
dealing with this topic has been already presented. In particular, several authors have suggested an integrated use of both
range and image information in order to increase the reliability and the completeness of the results exploiting their
complementary nature. In this paper, an integration between range and image data for the geometric reconstruction of
man-made object is presented. The focus is on the edge extraction procedure performed in an integrated way exploiting
both the from range and image data. Both terrestrial and aerial applications have been analysed for the façade extraction
in terrestrial acquisitions and the roof outline extraction from aerial data. The algorithm and the achieved results will be
described and discussed in detail.
KEYWORDS: Sensors, Laser scanners, Cultural heritage, 3D modeling, Active sensors, Projection systems, Cameras, Imaging systems, Standards development, 3D metrology
While 3D imaging systems are widely available and used, clear statements about the possible influence of material
properties over the acquired geometrical data are still rather few. In particular a material very often used in Cultural
Heritage is marble, known to give geometrical errors with range sensor technologies and whose entity reported in the
literature seems to vary considerably in the different works. In this article a deep investigation with different types of
active range sensors used on four types of marble surfaces, has been performed. Two triangulation-based active sensors
employing laser stripe and white light pattern projection respectively, and one PW-TOF laser scanner have been used in
the experimentation. The analysis gave rather different results for the two categories of instruments. A negligible light
penetration came out from the triangulation-based equipment (below 50 microns with the laser stripe and even less with
the pattern projection device), while with the TOF system this came out to be two orders of magnitude larger,
quantitatively evidencing a source of systematic errors that any surveyor engaged in 3D scanning of Cultural Heritage
sites and objects should take into account and correct.
Nowadays commercial software able to automatically create an accurate 3D model from any sequence of terrestrial
images is not available. This paper presents a methodology which is capable of processing markerless block of terrestrial
digital images to perform a twofold task: (i) determine the exterior orientation parameters by using a progressive robust
feature-based matching followed by a Least Squares Matching refining and a bundle adjustment; (ii) extract a dense
point-clouds by using a multi-image matching based on diverse image primitives. The final result is an accurate surface
model with characteristics similar to those achievable with range-based sensors. In the whole processing workflow the
natural texture of the object is used, thus images and calibration parameters are the only inputs. The method exploits
Computer Vision and Photogrammetric techniques and combines their advantages in order to automate the process. At
the same time it ensures a precise and reliable solution. To verify the accuracy of the developed methodology, several
comparisons with manual measurements, total station data and 3D laser scanner were also carried out.
KEYWORDS: 3D modeling, Data modeling, Laser scanners, 3D image processing, Data acquisition, Cameras, Systems modeling, 3D acquisition, Visualization, Global Positioning System
The digital documentation of monuments and architectures is an important field of application of the 3D modeling where
both visual quality and precise 3D measurement are important. This paper proposes an integrated approach based upon
the combination of different 3D modeling techniques for the virtual reconstruction of complex architectures like those
found in medieval castles. The need of combining multiple techniques, like terrestrial laser scanning, photogrammetry
and digital surveying comes from the complexity of some structures and by the lack of a single technique capable of
giving satisfactory results in all measuring conditions. This paper will address modeling issues related to the automation
of photogrammetric methods and to the fusion of 3D models acquired with different techniques, at different point
densities and measurement accuracies. The test bench is a medieval castle placed in Trentino A.A., a tiny region in
Northern Italy.
KEYWORDS: 3D modeling, Cameras, Laser scanners, Calibration, 3D image processing, Photogrammetry, Data modeling, Cultural heritage, Visualization, Active sensors
The generation of 3D models of objects has become an important research point in many fields of application like
industrial inspection, robotics, navigation and body scanning. Recently the techniques for generating photo-textured 3D
digital models have interested also the field of Cultural Heritage, due to their capability to combine high precision
metrical information with a qualitative and photographic description of the objects. In fact this kind of product is a
fundamental support for documentation, studying and restoration of works of art, until a production of replicas by fast
prototyping techniques. Close-range photogrammetric techniques are nowadays more and more frequently used for the
generation of precise 3D models. With the advent of automated procedures and fully digital products in the 1990s, it has
become easier to use and cheaper, and nowadays a wide range of commercial software is available to calibrate, orient
and reconstruct objects from images. This paper presents the complete process for the derivation of a photorealistic 3D
model of an important basalt stela (about 70 x 60 x 25 cm) discovered in the archaeological site of Tilmen Höyük, in
Turkey, dating back to 2nd mill. BC. We will report the modeling performed using passive and active sensors and the
comparison of the achieved results.
KEYWORDS: Cameras, Calibration, Distance measurement, Particles, Range imaging, Sensors, Digital filtering, Image segmentation, 3D metrology, 3D image processing
Range Imaging (RIM) is a new suitable choice for measurement and modeling in many different applications. RIM is a fusion of two
different technologies. According to the terminology, it integrates distance measurement as well as imaging aspects. The distance
measurement principle is dominated by the time-of-flight principle while the imaging array (e.g. CMOS sensor) enables each pixel to
store also the distance towards the corresponding object point. Due to the technology's relatively new appearance on the market, with
a few different realizations, the knowledge of its capabilities is very low.
In this paper we present our investigations on the range imaging camera SwissRangerTM (realized by the Swiss Center for Electronics
and Microtechnology, CSEM). Different calibration procedures are performed, including a photogrammetric camera calibration and
a distance system calibration with respect to the reflectivity and the distance itself. Furthermore we report about measurement
applications in the field of surveillance and biometrics. In particular, range imaging data of moving people are analyzed, to identify
humans, detect their movements and recover 3D trajectories.
KEYWORDS: 3D modeling, Clouds, Cultural heritage, Visualization, Sensors, 3D acquisition, Visual process modeling, Data acquisition, Head, Structured light
3D documentation and visualization of Cultural Heritage objects is an expanding application area. The selection of the
right technology for these kinds of applications is very important and strictly related to the project requirements, budget
and user's experience. Active sensors, i.e. triangulation based laser scanners and structured light systems are used for
many kinds of 3D object reconstruction tasks and in particular for 3D documentation of cultural heritage objects. This
study presents some experiences in the results of two case studies in which a close-range structured light system is used
for the 3D digitization. The paper includes all necessary steps of the 3D object modeling pipeline from data acquisition
to 3D visualization.
A photogrammetric strategy for the orientation of image sequences acquired by Mobile Mapping Vehicles (MMV) is presented. The motivations for this are twofold: to allow image georeferencing in short GPS outages for the MMV under development at the University of Parma, currently lacking an IMU; to improve the consistency of image georeferencing between asynchronous frames. The method may also contribute to limit the drift errors of low-cost integrated IMU/GPS systems in GPS outages. Drawing on techniques developed for structure and motion (S&M) reconstruction from image sequences and accounting for the specific conditions of the MMV imaging geometry, highly reliable multi-image matches are found, refining image orientation with a final bundle adjustment. Dealing with scenes with poor image texture and the automation of the convergence of the bundle to the solution are still problems. After successfully orienting image sequences up to about 200 m long, the accuracy of the orientation and reconstruction process was checked in a test field. Although not all constraints between synchronous image pairs are yet enforced, the accuracy degradation along the sequence was found to be still well within the specifications for the MMV. Furthermore curved path and possible solution to the poorness of tracked points are investigated.
The stability of a rock slope depends on the rock mass geo-structure and its discontinuities. Discontinuities show up at the rock surface as smooth and often plane surfaces. From their location and orientation the main families of fractures can be inferred and a stability analysis performed. To gather information on their distribution, surveys are typically carried out with geological compass and tape along scan lines, with obvious limitations and drawbacks. Here an highly automated image-based approach is presented to compute the required rock parameters: an accurate high resolution Digital Surface Model of the area of interest is generated from an image sequence and segmented in plane surfaces within a multi resolution RANSAC search, which returns location and orientation of each plane. To avoid measuring ground control points, the camera may be interfaced to a GPS receiver. Multiple overlapping and convergent images are captured to achieve good accuracy over the whole network, minimize occlusions and avoid poor object-camera relative geometry. The method is applied to the rock face of Corma di Machaby (Italy): the results are compared to those of a traditional survey with compass and to those of a laser scanner survey.
KEYWORDS: 3D modeling, Laser scanners, Photogrammetry, Solid modeling, Cultural heritage, Visual process modeling, Visualization, Medicine, Sensor calibration, Analog electronics
In the last decade, the demand of 3D models for objects documentation and visualization is drastically increased. 3D modeling of close-range objects is required in different applications, like cultural heritage, industry, animation or medicine. While Photogrammetry is a well proved technique for 3D reconstruction of real objects, featuring important properties like accurate sensor calibration, use of both analog or digital imageries, low cost and high portable system, laser scanning technology is becoming a very promising alternative for surveying and modeling applications. Tipically, laser scanners allow for fast acquisition of huge amount of 3D data which can be often combined with colour hi-res digital images. As a result, real objects can be represented with a higher level of detail together with a good metric accuracy. Among several works so far presented about laser scanning for cultural heritage survey, some modeling and accuracy related issues have been not yet solved and discussed in details. In this contribution we report about two case studies realized with photogrammetry and laser scanner and we provide some advices and suggestions about the more suitable 3D modeling method for a given object, taking into account its size and shape complexity, the required accuracy and the target application.
In the great valley of Bamiyan, north-west of Kabul, Afghanistan, two big standing Buddha statues were carved out of the sedimentary rock of the region around the second to fourth centuries AD. The larger statue was 53 meters high while the smaller Buddha measured 35 m. The two colossal statues were demolished on March 2001 by the Taleban, using mortars, dynamite, anti-aircraft weapons and rockets. After the destruction, a consortium was founded to rebuild the Great Buddha at original shape, size and place. Our group performed the required computer reconstruction, which serves as a basis for the physical reconstruction. The work has been done using three different types of imagery in parallel and in this paper we present our results of the 3D computer reconstruction of the statue.
Nowadays the interest in 3D reconstruction and modeling of real humans is one of the most challenging problems and a topic of great interest. The human models are used for movies, video games or ergonomics applications and they are usually created with 3D scanner devices. In this paper a new method to reconstruct the shape of a static human is presented. Our approach is based on photogrammetric techniques and uses a sequence of images acquired around a standing person with a digital still video camera or with a camcorder. First the images are calibrated and orientated using a bundle adjustment. After the establishment of a stable adjusted image block, an image matching process is performed between consecutive triplets of images. Finally the 3D coordinates of the matched points are computed with a mean accuracy of ca 2 mm by forward ray intersection. The obtained point cloud can then be triangulated to generate a surface model of the body or a virtual human model can be fitted to the recovered 3D data. Results of the 3D human point cloud with pixel color information are presented.
The goal of computing realistic 3-D models from image sequences is still a challenging problem. In recent years the demand for realistic reconstruction and modeling of objects and human bodies is increasing both for animation and medical applications. In this paper a system for the reconstruction of 3-D models of articulated objects, like human bodies, from uncalibrated images is presented. The scene is seen from different viewpoints and no pre-set knowledge is considered. To extract precise 3-D information from imagery, a calibration procedure must be performed. Therefore, first a camera calibration with Direct Linear Transformation (DLT) is done assuming few control points on the subject. The initial approximations of the interior and exterior orientation computed with DLT are then improved in a general photogrammetric bundle adjustment with self-calibration. Additionally a stereo matching process based on least squares matching extracts a dense set of image correspondences from the sequence. Finally a 3-D point cloud is computed by forward intersection using the calibration data and the matched points. The resulting 3-D model of human body is presented.
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