PHOTOGRAMMETRIC MAPPING WITH TOTAL STATION

Abstract

“Photogrammetric Mapping with Total Station (PMTS)” is a research work carried out for the purpose of integrating a powerful processing component with robotic total station and a photogrammetric system. Primary objective of PMTS is to provide a cost effective solution for precise measurement of 3D point cloud. The era of merging photogrammetry with angle measurement technology began with development of photo-theodolite (Porro, 1865). Up to till date all research works carried out in the area of PMTS are following the principle founded by developer of photo-theodolite. At present, photo-theodolite is replaced with advance robotic total station (IATS, 2005). Concept of scanning fuction was introduced by motorizing the total station (IASTS, 2007). Present trends in Photogrammetry are shifting from satellite Photogrammetry towards Close Range Photogrammetry (CRP). TS technologies are trending towards more and more automation, long range measurement, speed, precision, miniaturization, energy efficient and intelligent behavior, etc. Parallel to this, people throughout the world are working to bring both the technologies more close to each other for providing cost effective solutions with high quality results. Scanning Total Stations and Laser Scanning Devices have gained their popularity in providing solutions for 3D point cloud. The market is still dominated by photogrammetric systems for providing timely and cost effective solution of 3D point generation. All big manufacturer of the world had launched their high end products in the market. Laser scanner devices launched by them are Leica Scan Station C5, Trimble TX5, Topcon IP-S3, Topcon GLS 1500, Nikon insight L100, Leica Scan Station C10, Trimble TX8, FARO Focus 3DX 130, Topcon GLS 2000, Nikon XC65Dx, etc. Scanning Total Stations launched by them are Leica Viva TS 16, Trimble S7, Trimble S8, Trimble S9 and Topcon IS-3, etc. An integrated version of the two technologies is also available in the market e.g. Trimble XV comes with more advanced technologies. It is an example of Laser Scan Device integrated with Total Station. Besides high end technology is available in the market, but these devices come to be black boxes for their users. No one knows the real technology used by them in these devices. v Moreover they are very costly (more than Rs. 40 lakhs). For realization of the concept of “Make in India” and to develop an indigenous technology, the concept of PMTS is introduced in the research work presented here. In the first phase of development, reverse engineering was carried out for the purpose of understanding the existing technologies. After extracting internal architecture and instruction set of the robotic base, its overall control was transferred to computer system. For this purpose an interface and its library of subroutines were developed. It provides a service of communication channel between the robotic base and computer system. The interface also provides a facility to develop programs in high level language like C and Visual Basic, etc. for robotic applications of total station. This programming environment facilitates the users with a customizable environment for robotic applications at their own end. No more dependencies will be there on the manufacturer to fulfill day to day requirement after customized automation for the system. The controller which comes with robotic base was not capable in fulfilling all the requirements of the PMTS. Thus a powerful controller was developed in C language followed by its revised version developed in Visual Basic language. In the revised version of controller, a better GUI environment was provided to the users of PMTS. On successful implementation of first phase, its integration with photogrammetric system was carried out. The work was divided into two parts a) Mounting the camera on total station b) Optical orientation of camera system with telescope of total station. Major problem which is being faced throughout the world is to design the distortion model of the lens assembly. A new approach for modeling lens distortions was suggested for preparing distortion free model of camera used in PMTS. It was successfully completed and deployed. The concept of “WYSIWYG” (What you see is what you get) was used for modeling the distortions in lens assembly. In this phase of development, mapping of photo-coordinates to telescope coordinates were completed with precise results. On successful integration of camera system with total station, a sub system responsible for image assisted total station movement was developed. An approach for precise object targeting was successfully developed and was deployed in PMTS. This subsystem helped in replacing the functions of telescope in total station. Problem of narrow view of telescope was completely solved. Camera plays a dual role in PMTS. In its first role, it captures high resolution images of vi the field for photogrammetric use. Secondly, it provides a wider live view of the field for setting the targets to be measured. One problem was observed with scanning function. Total station was taking large amount of time for capturing field profile by using its scan function. Total stations are calibrated by the manufacturer for predefined values of environmental parameters like temperature, pressure and humidity, etc. There exists a provision of adjustment in measured values of target against change in value of environmental parameters. For it, current values of these parameters are to be entered in the total station for precise measurement of the target. During execution of scan function manual update of parameters is not feasible. A separate approach is proposed for online automatic updating environmental parameters into the total station. At the time of testing phase of PMTS, the system stopped responding, during its execution, twice or thrice in a week. To overcome this, a deep behavioral study of the system was done to find out sources or cause of errors. It was found that certain time critical operations during parallel communication with multiple devices, absurd targets, communication with slower devices, HD camera, complex real time expressions, etc. were responsible for system failure. A further solution was suggested for removal of these problems. In the end, after deployment of solutions for system failure, PMTS became a reliable system and no further system failure was observed. As a byproduct of the research work, a new finding for fixing the factual precedence of brackets in BODMAS was successfully registered in the copyright office of India.