Optical 3D measurement techniques in archaeology: recent developments and applications

This paper is intended to give an overview on current surveying techniques that use remotely sensed data, and their applications in archaeology. The focus is on optical 3D measurement techniques based on image and range sensors. Data and methods are briefly reviewed, whereas data processing and related problems are only touched on in passing. For the purpose of this review we distinguish three scales of archaeological research at which the surveying techniques discussed here can be applied: (1) the regional scale, to record the topography of archaeological landscapes and to detect and map archaeological features, (2) the local scale, to record smaller sites and their architecture and excavated features, and (3) the object scale, to record artefacts and excavated finds

Radiomeric and Geometric Analysis of Worldview-2 Stereo Scenes

WorldView-2 (WV-2) is DigitalGlobe's latest very high resolution optical sensor. Launched on October 8, 2009 and full operational since January 5, 2010, it flies along a sun-synchronous orbit at an altitude of 770km. The sensor is able to acquire panchromatic imagery at 0.46m ground resolution (0.52m at 20° off-nadir) and multispectral images in eight spectral bands at 1.8m resolution. In addition to the four typical multispectral bands (blue, green, red, near infrared), the sensors scans in the coastal (400-450nm), yellow (585-625nm), red edge (705-745nm) and near infrared-2 (860-1040nm) bands. Stereo images can be planned thanks to the ability of the sensor to rotate off-nadir up to +/-45°. This paper describes the investigations on WV-2 that are carried out at the EU Joint Research Center (JRC) in Ispra (Italy), by the ISFEREA Team of the Istitute for the Protection and Security of the Citizen (IPSC). The purpose of the study is to evaluate the radiometric and geometric properties of the sensor and its potentials for 3D information extraction. The images used for the analysis are a stereopair over North-West Italy, where ISFEREA has established a testfield. The radiometry of the images is evaluated through different methods, including the estimation of the noise level (standard deviation of the digital number) in homogeneous and non-homogeneous areas. The images are oriented with an RPC-based approach: using GCP (ground control points), the given Rational Polynomial Coefficients (RPC) are improved with an affine transformation to compensate residual systematic errors. The achieved accuracy is investigated by varying the number and distribution of GCPs. For automatic 3D information assessment, Digital Surface Models (DSM) are generated with different commercial software available at JRC and compared with reference data. The processing steps are described in the paper and the results discussed in detail.JRC.DG.G.2-Global security and crisis managemen

3D Modelling from Real Data

The genesis of a 3D model has basically two definitely different paths. Firstly we can consider the CAD generated models, where the shape is defined according to a user drawing action, operating with different mathematical “bricks” like B-Splines, NURBS or subdivision surfaces (mathematical CAD modelling), or directly drawing small polygonal planar facets in space, approximating with them complex free form shapes (polygonal CAD modelling). This approach can be used for both ideal elements (a project, a fantasy shape in the mind of a designer, a 3D cartoon, etc.) or for real objects. In the latter case the object has to be first surveyed in order to generate a drawing coherent with the real stuff. If the surveying process is not only a rough acquisition of simple distances with a substantial amount of manual drawing, a scene can be modelled in 3D by capturing with a digital instrument many points of its geometrical features and connecting them by polygons to produce a 3D result similar to a polygonal CAD model, with the difference that the shape generated is in this case an accurate 3D acquisition of a real object (reality-based polygonal modelling). Considering only device operating on the ground, 3D capturing techniques for the generation of reality-based 3D models may span from passive sensors and image data (Remondino and El-Hakim, 2006), optical active sensors and range data (Blais, 2004; Shan & Toth, 2008; Vosselman and Maas, 2010), classical surveying (e.g. total stations or Global Navigation Satellite System - GNSS), 2D maps (Yin et al., 2009) or an integration of the aforementioned methods (Stumpfel et al., 2003; Guidi et al., 2003; Beraldin, 2004; Stamos et al., 2008; Guidi et al., 2009a; Remondino et al., 2009; Callieri et al., 2011). The choice depends on the required resolution and accuracy, object dimensions, location constraints, instrument’s portability and usability, surface characteristics, working team experience, project’s budget, final goal, etc. Although aware of the potentialities of the image-based approach and its recent developments in automated and dense image matching for non-expert the easy usability and reliability of optical active sensors in acquiring 3D data is generally a good motivation to decline image-based approaches. Moreover the great advantage of active sensors is the fact that they deliver immediately dense and detailed 3D point clouds, whose coordinate are metrically defined. On the other hand image data require some processing and a mathematical formulation to transform the two-dimensional image measurements into metric three-dimensional coordinates. Image-based modelling techniques (mainly photogrammetry and computer vision) are generally preferred in cases of monuments or architectures with regular geometric shapes, low budget projects, good experience of the working team, time or location constraints for the data acquisition and processing. This chapter is intended as an updated review of reality-based 3D modelling in terrestrial applications, with the different categories of 3D sensing devices and the related data processing pipelines

Geometric and Optic Characterization of a Hemispherical Dome Port for Underwater Photogrammetry

The popularity of automatic photogrammetric techniques has promoted many experiments in underwater scenarios leading to quite impressive visual results, even by non-experts. Despite these achievements, a deep understanding of camera and lens behaviors as well as optical phenomena involved in underwater operations is fundamental to better plan field campaigns and anticipate the achievable results. The paper presents a geometric investigation of a consumer grade underwater camera housing, manufactured by NiMAR and equipped with a 7'' dome port. After a review of flat and dome ports, the work analyzes, using simulations and real experiments, the main optical phenomena involved when operating a camera underwater. Specific aspects which deal with photogrammetric acquisitions are considered with some tests in laboratory and in a swimming pool. Results and considerations are shown and commented

3D MODELING AND VIRTUAL APPLICATIONS FOR THE VALORIZATION OF HISTORICAL HERITAGE

[EN] A large amount of 3D digital models, acquired with reality-based techniques or modelled with CAAD methods, are today part of archaeological studies. This new form of heritage documentation has deeply changed the traditional way of representing, studying and visualizing the remains of the past. At the same time, 3D digital documentation is rarely shared and easily accessible, so as the historical iconographic sources, text documents and other information used forinterpreting remains and for validating 3D reconstructions. This paper describes the first results of an interdisciplinary project of 3D documentation and valorization of historical heritage, carried out in the archaeological site of Pausilypon (Naples, Italy). The final aim is to realize an integrated virtual tour of the site, developed in Unity 3D, based on 3D surveying products. This tour proposes a new way of presenting and visualizing results of archaeological studies and 3D documentation, collecting and overlapping different types of data in a unique and interactive virtual environment. Besides 360° equi-rectangular panoramic image and 3D models, heterogeneous material will help users to understand the interpretative process followed for the hypothetical CAAD reconstruction. These results will be mainly shared via web, for a larger dissemination of the work and for supporting future research on the site. In addition, for promoting the knowledge of the archaeological remains, a simplified and immersive tour will be developed for Virtual Reality devices.Farella, E.; Menna, F.; Remondino, F.; Campi, M. (2016). 3D MODELING AND VIRTUAL APPLICATIONS FOR THE VALORIZATION OF HISTORICAL HERITAGE. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 456-459. http://hdl.handle.net/10251/85988OCS45645

Progressive Keypoint Localization and Refinement in Image Matching

Image matching is the core of many computer vision applications for cultural heritage. The standard image matching pipeline detects keypoints at the beginning and freezes them until bundle adjustment, by which keypoints are allowed to move in order to improve the overall scene estimation. Recent deep image matching approaches do not follow this scheme, historically imposed by computational limits, and progressively refine the localization of the matches in a coarse-to-fine manner. This paper investigates the use of traditional computer vision approaches based on template matching to update the keypoint position throughout the whole matching pipeline. In order to improve the accuracy of the template matching, the usage of the coarse-to-fine refinement is explored and a novel normalization strategy for the local keypoint patches is designed. Specifically, the proposed patch normalization assumes a local piece-wise planar approximation of the scene and warps the corresponding patches according to a “middle homography”, so that, after normalization, patch distortion is roughly equally distributed within the two original patches. The experimental comparison of the considered approaches, mainly focused on cultural heritage scenes but straightforwardly generalizable to other common scenarios, shows the strengths and limitations of each evaluated method. This analysis indicates promising and interesting results for the investigated approaches, which can effectively be deployed to design better image matching solution

INVESTIGATING 3D RECONSTRUCTION OF NON-COLLABORATIVE SURFACES THROUGH PHOTOGRAMMETRY AND PHOTOMETRIC STEREO

Abstract. 3D digital reconstruction techniques are extensively used for quality control purposes. Among them, photogrammetry and photometric stereo methods have been for a long time used with success in several application fields. However, generating highly-detailed and reliable micro-measurements of non-collaborative surfaces is still an open issue. In these cases, photogrammetry can provide accurate low-frequency 3D information, whereas it struggles to extract reliable high-frequency details. Conversely, photometric stereo can recover a very detailed surface topography, although global surface deformation is often present. In this paper, we present the preliminary results of an ongoing project aiming to combine photogrammetry and photometric stereo in a synergetic fusion of the two techniques. Particularly, hereafter, we introduce the main concept design behind an image acquisition system we developed to capture images from different positions and under different lighting conditions as required by photogrammetry and photometric stereo techniques. We show the benefit of such a combination through some experimental tests. The experiments showed that the proposed method recovers the surface topography at the same high-resolution achievable with photometric stereo while preserving the photogrammetric accuracy. Furthermore, we exploit light directionality and multiple light sources to improve the quality of dense image matching in poorly textured surfaces

ACCURACY AND BLOCK DEFORMATION ANALYSIS IN AUTOMATIC UAV AND TERRESTRIAL PHOTOGRAMMETRY – LESSON LEARNT –

International audience; The paper rep orts the results of an integrated Unmanned Aerial Vehicle (UAV) and terrestrial photogrammetric survey realized in the archaeological site of the Roman theatre in Ventimiglia, Italy. The main deliverables were 2D drawings at scale 1:20, which required a Ground Sample Distance (GSD) less than 4 mm and, consequently, accuracy better than 4 mm. The UAV was employed to acquire both vertical and oblique images, while the terrestrial imaging acquisition was realized with the aim of generating separate dense point clouds of some vertical structures, corresponding to the sections required. The variability of results with automatic photogrammetric procedures against different image network configurations, with and without ground control, are analyzed and presented

3D virtualization of an underground semi-submerged cave system

Underwater caves represent the most challenging scenario for exploration, mapping and 3D modelling. In such complex environment, unsuitable to humans, highly specialized skills and expensive equipment are normally required. Technological progress and scientific innovation attempt, nowadays, to develop safer and more automatic approaches for the virtualization of these complex and not easily accessible environments, which constitute a unique natural, biological and cultural heritage. This paper presents a pilot study realised for the virtualization of 'Grotta Giusti' (Fig. 1), an underground semi-submerged cave system in central Italy. After an introduction on the virtualization process in the cultural heritage domain and a review of techniques and experiences for the virtualization of underground and submerged environments, the paper will focus on the employed virtualization techniques. In particular, the developed approach to simultaneously survey the semi-submersed areas of the cave relying on a stereo camera system and the virtualization of the virtual cave will be discussed

AUTOMATED AND ACCURATE ORIENTATION OF COMPLEX IMAGE SEQUENCES

The paper illustrates an automated methodology capable of finding tie points in different categories of images for a successive orientation and camera pose estimation procedure. The algorithmic implementation is encapsulated into a software called ATiPE. The entire procedure combines several algorithms of both Computer Vision (CV) and Photogrammetry in order to obtain accurate results in an automated way. Although there exist numerous efficient solutions for images taken with the traditional aerial block geometry, the complexity and diversity of image network geometry in close-range applications makes the automatic identification of tie points a very complicated task. The reported examples were made available for the 3D-ARCH 2011 conference and include images featuring different characteristics in terms of resolution, network geometry, calibration information and external constraints (ground control points, known distances). In addition, some further examples are shown, that demonstrate the capability of the orientation procedure to cope with a large variety of block configurations