Bu çalışmada, yapı elemanlarının dinamik yük deneylerinde yer değiştirmelerin izlenmesinde kullanılmak üzere videogrametrik bir sistem tasarımı yapılmıştır. Sistem, yazılım ve donanım olmak üzere iki bileşenden oluşmaktadır. Borland C++ builder programlama dili kullanılarak geliştirilen yazılımda, video kameralardan görüntü alma, hedef görüntülerin resim koordinatlarını piksel altı doğrulukta ölçme, görüntü eşleme ve ek parametrelerle demet dengelemesi gibi birçok fonksiyon sunulmuştur. Sistemin donanım bileşeni ise, üç adet Basler A302fc video kamera, PCI IEEE 1394 arabirim kartı, bağlantı kabloları ve kalibrasyon cismini içermektedir. Sistemin ölçme prensibi kısaca, kamera parametre ve konum bilgilerinin belirlendiği sistem kalibrasyonu ve sonra tanımlanan zaman aralıklarında ya da yükleme sonrası, sabit kamera konumlarından yapı elemanı üzerindeki ilgili noktaların üç boyutlu koordinatlarının uzaysal ileriden kestirme dengelemesiyle hesaplanması ilkesine dayanır. Görüntülerin elde edilmesinden yapı elemanı üzerindeki işaretli noktaların 3 boyutlu koordinatlarının hesaplanmasına kadar bütün işlem adımları gerçek zamana yakın biçimde sistem içerisinde çözülebilmektedir. Test edilmesi amacıyla sistem, zemin numunelerinin serbest basınç deneylerinde kullanılmış ve ölçme sonuçları, deney aletinden okunan ölçme değerleriyle karşılaştırılmıştır. Geliştirilen sistemle gerçekleştirilen fotogrametrik değerlendirmelerde, her bir deney için resim koordinat düzeltmelerinin karesel ortalama hata değerleri, 0.02 pikselle 0.05 piksel aralığında elde edilmiştir. Cisim koordinatlarının ortalama prezisyonu ise X ve Z doğrultularında 16 μm, Y doğrultusunda, 62 μm olarak hesaplanmıştır.

The testing and monitoring of structures and structural components under different loading conditions are a standard engineering application. Geometrical measurements are performed for the examination of the behavior of test objects and for the verification of theories or mechanical models. This is often realized by static, quasi-static, or dynamic short and long time load experiments on test objects. In these tests, it is demanded to determine parameters and effects such as the changes in shape, load and strain which are commonly measured by LVDTs, extensometers and strain gauges. These devices provide on-line results with a high geometric precision and reliability. A general disadvantage of these techniques, however, is their point wise and only onedimensional measurement capability. The techniques are generally not suited for tasks requiring a large number of measurement points distributed over an object surface or for complete surface measurements. In these cases, techniques of digital photogrammetry depict a valuable option for the design of powerful and flexible measurement tools. However, while the measurement of the absolute coordinates and the movement of signalized targets on an object can be solved by commercial software packages, non standard monitoring tasks or applications with real time or near real time requirements will often necessitate the development of customized software tools. In this study, a videogrammetric system is developed to measure the coordinates of signalized targets on structural components during both dynamic and static load tests. After the system calibration, the entire process from acquisition multi image sets to computation of 3D object coordinates are solved by the system at almost real time. The system consists of two basic components: hardware and software. The software which was developed by using Borland C++ builder programming language presents many functions such as acquiring images, locating targets and calculating their centroids, converting target centroids to spatial coordinate in object space, and computing displacement. The hardware component of the system comprises of 3 Basler A302fc video cameras, PCI IEEE-1394 interface card, connecting cables and calibration object. The entire measurement process is realized as a two-stage process which are a preliminary offline phase and online photogrammetric triangulation process. Offline photogrammetric processing stage includes system calibration which is defined as the calibration and orientation parameters of all the components involved in the acquisition system and a zero measurement. Camera calibration refers to the determination of the parameters describing the internal geometry of the individual imaging devices and other parameters modeling the systematic errors caused by the optical system and other sources. Camera orientation includes the determination of the parameters of exterior orientation to define the camera station and camera axis in the 3D space. After orientation procedure, it is required that the cameras ought to stable during the entire measurement process. For zero measurement, images of the test object on which the signalized targets are placed are acquired firstly. Then, the image coordinates of all targets are measured with sub-pixel accuracy automatically via intensity weighted centroiding. Afterward, matching process is implemented to establishment of correspondences in the multi-images. Finally the 3D coordinates of the matched points are computed by forward ray intersection using the results of the calibration process. The main aim of on-line data processing was the determination of the displacement values at each measurement epoch associated with the current loading. Online photogrammetric processing stage is composed of three steps as follows: the simultaneously acquisition of multi-image sets of the structural element at defined time intervals or after load applications; the measurement of the image coordinates of targets which are labeled in the zero measurement and computation of the 3D coordinates of the points whose image coordinates are measured. The system was used for unconfined compression tests in order to demonstrate the functionality of it and measurement results obtained from two different systems obtained were compared. This study has been shown that the developed system was successfully employed to determine the displacement measurements in structural components during loading tests. The achieved average theoretical precision is about 16 microns in the X and Z directions and about 62 microns in the Y direction. The RMS value of image co-ordinate residuals which are important quality indicators was determined between 0.02 and 0.05 pixel.