Comprehensive positional accuracy improvement (PAI) for National Digital Cadastral Database (NDCDB)

Driven by the need for increased efficiency, traceability, and positional accuracy in land records, cadastral representation has undergone significant changes through modernisation efforts. However, establishing the cadastral database from various sources and the quality of data has yielded uncertain deliverables, as stated in Circular Department of Survey and Mapping Malaysia (DSMM) 01/2010. To address the limitation, this study focused on achieving a comprehensive procedure for improving the positional accuracy of the National Digital Cadastral Database (NDCDB) by exploiting the secondary cadastral datasets. The investigation began by identifying a comprehensive datum framework that utilises global navigation satellite system (GNSS) static and rapid static solutions for primary and secondary control networks, respectively. As an alternative to the absolute traversing approach, the study has examined the opportunities to integrate the GNSS baseline vectors with traverses in connecting the network constraints and cadastral record (i.e., NDCDB). Considering the fundamental drawback of the indirect approach that suffers from error propagation, a direct observation method, emphasising angles over conventional bearing-based techniques, is employed to improve the solution of the cadastral network adjustment. This approach leverages angular measurements taken directly between observation points, reducing the dependency on fixed bearings derived from a reference direction. To verify the reliability of the proposed comprehensive solution in enhancing the positional accuracy of the cadastral record, a partial cadastral block located in Jejawi, Perlis, has been systematically reprocessed and evaluated. The results demonstrated that implementing independent baseline adjustments for the primary control and the resection technique for the secondary control yielded coordinate standard deviations ranging from 0.6 cm until 0.9 cm, within the allowable tolerance of less than 1 cm. By integrating GNSS baseline vectors with cadastral records to form a hybrid solution, the findings reveal that this approach yields results comparable to the traversing method. Furthermore, the hybrid solution requires minimal instrumentation and significantly reduces the effect of error propagation. The use of an angle-based approach yielded superior results in the chi-square test, achieving lower bounds or the level passed compared to the bearing solution, which was limited to achieving upper bounds. Furthermore, the implementation of the angle-based method significantly enhanced positional accuracy for cadastral records, achieving coordinate RMSE values between 0.039 m and 0.057 m particularly for certified plans of the first and second classes. In conclusion, this research enhances the NDCDB by providing comprehensive techniques that improve positional accuracy to below 10 cm, while maintaining parcel area differences between 0.6 and 0.7 percent, well within the 5 percent limit specified in DSMM Survey and Guideline Circular No. 6/2009. These findings are essential for the modernisation of NDCDB and the enhancement of land administration systems, in accordance with the Sustainable Development Goals (SDGs) emphasised by the United Nations.