Strategy development for terrestrial laser scanning measurements

The period we live in is a period that people produce real-world models by measuring the objects that are around them to regulate and manage their relationship with the environment they live in. Gaining knowledge by analyzing the generated models has become an effective tool used in human and environment related decision making processes. The level of technological development we have today has changed the content and quality of information used in many areas. All information produced about an object is not necessarily related to its position or shape. However, technological possibilities have begun the process of forming data sets, in which various pieces of information about an object are integrated with each other and express stronger meanings. The 3D information and information systems where 3D information is being used are expanding their usage area. Therefore 3D data acquisition is one of the most popular workspaces of today. Terrestrial laser scanners (TLS) produce point clouds with a near-realistic image of the scanned object with high-accuracy coordinate data gathered from its surface. TLS can overperform even if the measured object has a complex shape or a difficult position to reach. Due to this feature, TLS is more effective than other measurment instruments. Point clouds produced by TLS are one of the most practical and accurate measurement outputs used for 3D model production. TLS measurements can be used to solve many problems in different areas. The final products required in each of these areas can be produced with high accuracy and speed by TLS. TLS's success in different areas has allowed it to increase its use as a highly reliable measuring instrument. TLS, defines a general group of measurement instruments; they have different measurment principles, use lasers in different wave lengths, and represent the entirety of different devices in design. There are many TLSs with different characteristics. These properties also change the structure and quality of the point clouds obtained. This situation brings along the question of which scanner to use for which objects. To obtain the point cloud data with the required quality; it is important to use the right device, to apply the right methods, to eliminate measurement errors, and to make them within a strategy. xxx Achieving maximum performance in a laser scanning measurement depends on the characteristics of the scanner, the size and shape of the scanned object, and the physical conditions of the measurement environment. All of these factors have different effects on the point cloud produced. That's why; the practitioners should have the technical knowledge about both the TLS they are using and the data needed for the applications. Developing a strategy in a measurement work can not be made without directing technical informations about the work to be performed. In order to develop a strategy in TLS measurements, it should be assumed that the work being done is a 3D data production work. For this reason, focusing on the required output, the qualities of the data to be produced must be well understood. Even though TLS are highly effective devices, they can give their best performance when they are integrated with other measurement techniques. The requested output is not likely to be the only raw point cloud. It is quite common for point clouds to be located in a geodetic coordinate system, containing high-resolution color information, and being digital objects that can be easily analyzed through mainstream software. Therefore, practitioners must have a professional vision and measurement strategy that can meet the expectations of the laser scanning work. In the context of this Thesis; developing a strategy for terrestrial laser scanning measurements has a setup which created in three main steps. The vision practitioners must have in the work of producing 3D data has been explained in these three basic steps. Each of the steps leads and enhances the next one. The main idea of the Thesis is that working in accordance with a specific plan will benefit 3D data production and it should be included as a standard procedure in every work. In the first step of the measurement strategy; a TLS practitioner must analyze his / her experience with his / her scanner and personal technical knowledge. As a result of this analysis, the practitioner must determine his / her 3D data production capacity. For this, it is necessary to examine the measuring instrument used at first. TLS is a device that can acquire point clouds with high accuracy of object surface in a very short time. This feature can become misleading for both practitioners and clients. However, error sources in TLS measurements are quite important, and each practitioners should have full knowledge of this subject. The concept of error in geomatics engineering means that a different measurement result value is obtained from a known (measured) value and indicates a detectable deviation. A measurement error is a possible condition for geomatics engineering. Starting from this, geomatics engineering is a discipline in which measurement error calculations, detection of measurement errors and estimation of possible errors in the measurements are done. Since this thesis is written with understanding and knowledge of geomatic engineering, error sources in TLS measurements are processed as an important parameter of measurement strategy. Evaluating a scanner to measure any object can be accomplished by knowing the device's measurement principles and the laser characteristics it uses. When practitioners examine a device, they should be able to understand all the information contained in the device's data page and make predictions about the overall performance of the device with the information it receives from each technical parameter. At the same time, it is also important to know that this presentation information may not reflect the actual performance of the devices. In academic performance tests conducted with scanners, the devices have different results from the brochure information, indicating that this information should not always be xxxi trusted. TLS is a device produced in very small series and the mechanical designs are kept extremely secret. It is seen that the devices in the same series can give different measurement results even with small differences. The same research shows that devices can achieve the ideal measurement performance with careful use and regular calibration. It is a recommended practice for practitioners to test the performance of their devices they use regularly, even in simple ways. When a practitioner has enough knowledge about the scanner he is using and the error sources in TLS, he can produce point clouds in high quality. Point clouds can be kept away from specific measurement errors by taking certain conditions into consideration and using auxiliary equipment before the measurement process. However, after the measurement process, faulty parts of point clouds can be cleaned up by some softwares or removed from the measurement data set. A point cloud must be absolutely optimized before it is transformed into a product. Another step in developing a measurement strategy is to understand the needs of the client. TLS is used to meet the needs of many disciplines in their wide range of uses. Understanding the needs of people from every discipline working together is an important experience that practitioners will gain. The negotiations with the client during the planning of a measurement task are very important. Because the resulting product requested by the client will directly affect the scanning process. Based on the product requested, practitioners can do geodetic measurements for georeferencing and can choose specific targets for this process or make a plan for terrestrial photogrammetry study. A practitioner should be aware of the resulting product variety that the client can offer by analyzing the strategy developer's first step. It is necessary to know which of these products will meet the needs of the client. Generally, persons or institutions who request laser scanning measurement, do not have knowledge of this measurement technique and other geodetic measurements. While they inform the practitioner about the qualities of the data they need, they do not have any information about which measurement technique they want to use either. In this sense, practitioners should provide guidance service to clients if it is necessary. Therefore, understanding the need of the client is the fundamental step in developing a measurement strategy. In negotiations with the client; It is important that the practitioners act with the thought that it is a 3D data production work. The outcomes client requires can be the data that can be generated by other measurement techniques, such as with TLS. However, achieving the required outcome may be possible not only by using TLS but by integrating multiple measurement techniques. Then, the technical information about the other measurement techniques of the practitioners will become important. Practitioners will have the advantage of thinking of the work they are doing as a 3D data production work. If necessary, it is an advantage for practitioners to make integrated measurements with terrestrial measurement techniques (total station, GPS etc.), terrestrial photogrammetry or other laser scanners. xxxii Processing point clouds, includes all the work done to produce the outcome. 2D plans and sections can be generated from point clouds, as well as various 3D models. 3D models are the most comprehensive and highest quality products that can be produced for an object. The physical characteristics of the modeled object can change the software used modelling process or increase the effort that the practitioner needs to demonstrate. The most time-consuming step of producing 3D data is the modelling process. Then, the ability of practitioners to use software becomes important. There are a variety of modeling software on the market. Some software developer companies have developed specialized software to produce models of specific objects. There are also versions of these software that can be installed as plug-ins to the mainstream CAD programs. It is estimated that there are hundreds of companies working on 3D data work, and also there are companies that do this work in our country. The ability of practitioners to use software directly affects the resulting product quality. Using the most appropriate software for different objects may seem like the ideal solution, but in general it does not matter which software is selected. While deciding to choose the right software; the practicality of use and the resulting product diversity should be taken into consideration. Laser scanning technology has created a work field that includes point cloud processing and modeling software developing. It is seen that new works are being made every day in this field and new hardwares and softwares are being put on the market. Strategy development work should be a process that can constantly renew and improve itself through the analysis processes and evaluation of success at the end of the work. In this process; it should be taken into consideration that the using equipment and software are insufficient. For this purpose, replacement and development attempts need to be done by following the developing technology. The increased use of TLS also means the appearance of different clients in the future. Therefore; for every practitioner who has gained working habits with the right strategy, it will not be difficult in this process, renewing itself. In this thesis; preliminary studies and what to think about during the laser scanning measurement are explained. And also, in the general sense, optimum solutions for obtaining 3D data of an object by TLS, are presented. Working based on a specific strategy, mentioned the benefits to practitioners and was asked to serve as an example for practitioners.