Study of weighted fusion methods for the measurement of surface geometry

Four types of weighted fusion methods, including pixel-level, least-squares, parametrical and non-parametrical, have been classified and theoretically analysed in this study. In particular, the uncertainty propagation of the weighted least-squares fusion was analysed and its relation to the Kalman filter was studied. In cooperation with different fitting models, these four weighted fusion methods can be applied to a range of measurement challenges. The experimental results of this study show that the four weighted fusion methods compose a computationally efficient and reliable system for multi-sensor measurement problems, especially for freeform surface measurement. A comparison of weighted fusion with residual approximation-based fusion has also been conducted by providing the input datasets with different noise levels and sample sizes. The results demonstrated that weighted fusion and residual approximation-based fusion are complementary approaches applicable to most fusion scenarios

YERSEL LAZER TARAYICI NOKTA BULUTLARININ BİRLEŞTİRİLMESİ VE JEODEZİK KOORDİNAT SİSTEMİNE DÖNÜŞTÜRÜLMESİ: LİTERATÜR ARAŞTIRMASI

YERSEL LAZER TARAYICI NOKTA BULUTLARININ BİRLEŞTİRİLMESİ VE JEODEZİK KOORDİNAT SİSTEMİNE DÖNÜŞTÜRÜLMESİ: LİTERATÜR ARAŞTIRMASIÖzetYersel lazer tarayıcılarla üç boyutlu (3B) modelleme çalışmalarında, nokta bulutlarının birleştirilmesi en önemli işlem adımlarından birisidir. Bu amaçla bugüne kadar pek çok yöntem geliştirilmiştir, ancak lazer tarayıcı nokta bulutlarının birleştirilmesi hala önemli bir araştırma konusudur. Diğer yandan nokta bulutlarının otomatik birleştirilmesi de ciddi bir araştırma konusudur ve her türlü veri seti için uygulanabilecek standart bir yöntem bulunmamaktadır. Uygulanan yöntemler; otomasyon, doğruluk, hesaplama süresi, nokta yoğunluğu ve ölçü hatalarına duyarlık bakımından farklılıklar göstermektedir. Ayrıca lazer tarama verilerinin başka konumsal verilerle entegrasyonu için jeodezik koordinat sistemi gibi ortak bir koordinat sistemine dönüştürülmesi gerekir. Ölçme tekniği ve lazer tarayıcı aletinin konfigürasyonuna bağlı olarak jeodezik koordinatlandırma yöntemleri değişiklik göstermektedir. Bu çalışmada lazer tarayıcı nokta bulutlarının birleştirilmesinde kullanılan yöntemler sınıflandırılmış ve belirli özellikleri vurgulanmıştır. Böylece nokta bulutlarının birleştirilmesi ve jeodezik koordinat sistemine dönüştürülmesi konusunda uygulayıcı ve araştırmacılara yol gösterici olunması amaçlanmıştır.Anahtar Kelimeler: Yersel lazer tarama, Nokta bulutu, Birleştirme, Üç boyutlu dönüşüm, LIDAR, Jeodezik koordinatlandırma.REGISTRATION AND GEOREFERENCING METHODS FOR POINT CLOUDS OF TERRESTRIAL LASER SCANNER: A REVIEWAbstractPoint cloud registration is bottle neck on three-dimensional (3B) modelling by using terrestrial laser scanner. Many methods have been developed for the registration of point clouds so far. Neverthless, it is still important research topic. Automatic registration of point clouds is also one of the important research topic on three-dimensional modelling. There are no standart methods for applying all type of data sets. The registration methods have different specicifications in respect to automation, accuracy, computation time, point density and susceptiblity from irregular points. On the other hand, the point clouds have to be registered into extensive coordinate system like this geodetic system for the integration with the other spatial data. Georeferencing methods of point clouds change according to measurement methods and configuration of laser scanner instrument. In this study, point cloud registration methods have been classified and emphasized their main properties. Thus, it had to be given informataion for the applicants and researchers about point cloud registration and georeferencing.Keywords: Terrestrial laser scanning, Point cloud, Alignment, Three-dimensional registration, LIDAR, Georeferencing

Virtual 3D Reconstruction of Archaeological Pottery Using Coarse Registration

The 3D reconstruction of objects has not only improved visualisation of digitised objects, it has helped researchers to actively carry out archaeological pottery. Reconstructing pottery is significant in archaeology but is challenging task among practitioners. For one, excavated potteries are hardly complete to provide exhaustive and useful information, hence archaeologists attempt to reconstruct them with available tools and methods. It is also challenging to apply existing reconstruction approaches in archaeological documentation. This limitation makes it difficult to carry out studies within a reasonable time. Hence, interest has shifted to developing new ways of reconstructing archaeological artefacts with new techniques and algorithms. Therefore, this study focuses on providing interventions that will ease the challenges encountered in reconstructing archaeological pottery. It applies a data acquisition approach that uses a 3D laser scanner to acquire point cloud data that clearly show the geometric and radiometric properties of the object’s surface. The acquired data is processed to remove noise and outliers before undergoing a coarse-to-fine registration strategy which involves detecting and extracting keypoints from the point clouds and estimating descriptions with them. Additionally, correspondences are estimated between point pairs, leading to a pairwise and global registration of the acquired point clouds. The peculiarity of the approach of this thesis is in its flexibility due to the peculiar nature of the data acquired. This improves the efficiency, robustness and accuracy of the approach. The approach and findings show that the use of real 3D dataset can attain good results when used with right tools. High resolution lenses and accurate calibration help to give accurate results. While the registration accuracy attained in the study lies between 0.08 and 0.14 mean squared error for the data used, further studies will validate this result. The results obtained are nonetheless useful for further studies in 3D pottery reassembly