Laser Scanning and Photogrammetric Evaluation of Uzuncaburç Monumental Entrance #

This studied in Ayaş, Erdemli the town of Mersin. In this study it is aimed 3D modeling of Historical Uzuncaburç monumental entrance by the using of both methods; Terrestrial Laser scanning, Terrestrial photogrammetric methods. At first, it is coordinated with the targets which are studied on the historical gate. These coordinates are approved as the the reference coordinates. The coordinates of these targets are obtained with help of both terrestrial laser scanning and terrestrial photogrammetric method. These coordinates are compared with the accurate coordinates and made a sensibility research. In this project Optech laser scanner is used to obtain 3D point datas. These point clouds are combined by Polyworks software and the terrestrial photogrammetric drawings are done by Photomodeler software.


Introduction
In recent years ,the use usage of laser scanning systems on 3D modeling works is increasing. In this system the modeling of the objects are done with the help of point cluster. All points which are in the point clouds, have 3D coordinates. In a few minutes thousands of 3D points can be obtained about the mentioned object. Terrestrial object has been used for this used for this purpose for years. Terrestrial laser scanning is a quite new method for 3D modeling. Although terrestrial laser scanning has some disadvantages, it has important advantages. These advantage scan be listed below; directly obtaining the 3D points, quite effective on defining the formless structures, and obtaining the results in a short time. Limited distance, high imaging expenditure and not obtaining the attribution of the object, are the primary disadvantages [1].

Terrestrial Laser Scanning Technology
Terrestrial laser scanning technology is a new developing technology which is used for 3D modeling of the objects. Today, the most popular measuring system for laser scanners is "Time of flight". This technique enables to measure the identified distance for several 100 meters. Besides, phase measuring principle is another partner technique. At this technique distance is limited in 100 meters. Accuracy of measured distance is just a few mm. Some terrestrial laser scanners can measure up to several m. Those are used in more industrialized applications. Optic triangulation is the kind of distance measuring principle which is used in this kind of terrestrial laser scanners. The accuracy of these measures are at micron levels. Terrestrial laser scanners can be group according to their technical features below [2][3][4][5]. both sides of the middle one. The coordinates are 36 o 34' 53,8"north, 33 o 55' 25,60" east ( Figure 1). The 3 arched structure has 31 meters length and 12 meter high. The gate is dated in 2 nd century AD. This gate is one of the most important structures of the historical city because there is a tablet on it which is written the name of the city, "Diokaesareia". By this tablet, we are able to learn that this gare was restored the roman imsikketor Arcadius (AD 395-408) and Honorius (AD 395-423).

4-Material-Method
Two different technique is used to complete the work at filed. First one is terrestirial laser scanning, the other one is photogrammetric. During the pre-study process of modeling , the Uzuncaburç gate, laser scanning tool and electronic total station ( Figure  After the preparations had finished at the field, the measurement of the control points at the study started. Angles and distances are measured by Total Station GPT 3007 laser and vertical, horizontal and oblique distances are measured by laser Total Station ( Figure 5). And also coordinates are obtained with these devices.

The application of terrestrial laser scanning at Uzuncaburç Gate
The study which we applied has two process. One is at the area, the other one is at the office. The area work includes scanning the area with laser scanning devices. Office work includes the transferring of data to computers or to suitable applying devices which is obtained during the area work. The area work takes 1 day and Office work takes 3 days long. The scanning of the castel gate with terrestrial laser scanning is applied on six different scanning station. Each scanning is applied at the partner points with in at least 4 link points. The scanning process is applied Optech Ilris 3D laser scanning device with in 1 cm points density. The scanning process is controlled by its own controller programme of the scanner "controller" (Figure 6 and 7).  The interface of parser programme The files, whose extension are transformed, then opened with polyworks programme and combined with it. The combination process is applied while two different point clouds partner point is is defined. At the end of this process, the point clouds of the castle gate is obtained (Figure 9 and 10).

4.2.The application of the terrestrial photogrammetric method at Uzuncaburç gate
First of all photography work is completed in terrestrial photogrammetric study. Photographing was made by Nikon camera D3100 (Figure 11 and 12).

Findings
The 20 paper points (Figure 15) which are stuck on castle walls, are coordinated by total station. The coordinates are confirmed as the exact coordinates.    At this grade, the sensibility standards are calculated weightily. S o =20m unit distance is chosen as the average distance between total station and the object points, weight Pi= 20/si equality is determined for each point (Table-3). With the help of weightedly found results point cloud changes is tried to be identified.3D location accuracy is calculated as in formula (1). [4]. (1) As a result of weighted evaluation location accuries which are calculated for each point,are calculated according to formula (2) and the results are given at Table-4.  Both standart deviation values of weighted standart and 3D location accuracies for each points are obtained from formula(3) ( Table-5). t-test is applied considering the coordinate differences and their standard deviation is known during the examining of whether the coordinate differences are meaning or not. Calculated test greatness is given in Table-6.These values are compared degrees of freedom (f=n-1) and error probability α=0.05 with in the limit value at t-chart.t-test limit value is (Considerin degrees of freedom f=20-1 and error probability α=0.05) 2.09.

Results
Terrestrial laser scanning technology which boots the creation of 3D modeling studies, has been started to use widely day by day. It has been presenting an important role as it is faster and more practical on the studies of especially preserving historical and cultural heritages, relieve and documenting studies. The sensibilities ,obtained at both methods, reached us a conclusion with these techniques that they could be base for further restoration works. In conclusion of these documenting techniques. it is understood that by sending the documents to their appropriate usage opportunities ,there can be a data interaction between different disciplines ,and a decrease on expenditures. The usage of this system is getting wider ,especially in engineering, and it ensures advantages like time ,cost and labor decreasing. Considering that coordinate differences and their standard deviating are calculated-test is applied in order to understand whether the coordinates(obtained both total station and laser scanner) are meaningless or not. When t-test results are examined ,it is seen that all results are below the limited values.