Improving the Positional Accuracy of Digital Cadastral Maps through Optimal Geometric Transformation

AbstractThis paper presents an attempt to reduce positional errors in digital cadastral maps produced by digitization (scanning, georeferencing, and vectorization) of existing Bosnian-Herzegovinian analog (paper-based) maps. The geometric content of the digital cadastral maps generated by the aforementioned procedure is encumbered by nonuniform and irregularly distributed positional distortions. Errors created during the original elaboration of the analog maps (based on hand drawings using the drafting instruments) cannot be corrected through the geometric transformation of the cadastral map with the use of common (tie) points on the map coordinate grid. This study focused on the elimination of errors in the original map drafts through better selection of common points, with the aim of obtaining a homogeneous spatial accuracy of cadastral maps. With the use of the flexible thin plate spline (TPS) transformation model, which includes information on systematic distortions caused by errors of the original mapping process, the authors made a significant step toward the enhancement of the positional accuracy of boundary points in the digital cadastral maps. The use of TPS transformation reduces heterogeneity of each cadastral map, and maps are efficiently georeferenced to the state plane coordinate grid. Digital cadastral maps generated by reconstruction of original state survey measurements are typically more accurate than those obtained by digitizing scanned maps, and these types of maps were not considered in this study.