OPTIMIZING MAP PROJECTIONS FOR EQUILIBRIUM AND MINIMAL DISTORTION IN PROVINCIAL CONSTRUCTION PROJECTS

Abstract

The Universal Transverse Mercator (UTM) projection is widely used in design and construction projects in Thailand. However, in some areas, it may introduce linear distortions of up to 965 ppm. Therefore, the linear distortion caused by the UTM projection is considered a significant systematic error. This study investigates the design of Low Distortion Projections (LDP) at the provincial level, including Transverse Mercator (TM), Lambert Conformal Conic Projection (LCC), and Oblique Mercator (OMC). The research highlights the importance of "urban areas," where construction frequently occurs. These areas often have terrain elevations higher or lower than the average topographic surface, necessitating the development of a provincial LDP with a Combined Scale Factor (CSF) between -20 ppm and +20 ppm, covering over 80% of urban areas.Furthermore, an optimal balance for construction project LDPs is sought, with CSF values ranging between -10 ppm and +10 ppm.Using Phayao Province as a case study, specifically the Denchai - Chiang Rai - Chiang Khong railway project, Contract 2 (Ngao - Chiang Rai section), it was found that the Transverse Mercator LDP was the most suitable. This projection resulted in a provincial CSF range of -18 to +17 ppm and a project-specific CSF range of -8 to +8 ppm. Horizontal and vertical distortions were also analyzed using LDP parameters from control points within the project. The results revealed horizontal and vertical deviations ranging from -6 to +6 millimeters, demonstrating that a combined scale factor was unnecessary in practice. Selecting an appropriate LDP can significantly reduce errors in design and construction caused by map distortions. It is anticipated that Low Distortion Projections will play a more prominent role in Thailand's construction industry in the future.