Rod Thompson

Development of validation rules to support digital lodgement of 3D cadastral plans

Abstract Validation is a familiar topic in computing, generally as a mechanism to protect a database from the effects of inappropriate data with the side effect of detecting some errors. As such, the validation rules are determined from the database schema using well understood methodologies. This paper takes a different view by examining digital validation as one of a set of processes that are designed to ensure that the incoming data (in this case, a plan of cadastral survey) is unambiguous and contains sufficient detail to define the legal spatial extents of a property. This is a complex question, especially since the rules and the decisions based on these processes must be defensible (therefore cannot contain arbitrary requirements imposed by a specific database model). Using the jurisdiction of Queensland, Australia, as a case study, this paper discusses the manual submission and lodgement of cadastral survey plans and the current 2D digital process as precursors to the automatic lodgement of all plans of survey. A set of validation rules is proposed for application to single geometric objects, to the relationship of objects on a single survey plan, and to objects that are independently defined on separate plans. It is asserted that, by the nature of the problem, this set is incomplete and will remain so. However, this research has identified a “checklist” of issues to be addressed by jurisdictions hoping to implement digital cadastral survey plan lodgement. The implications of this work in the context of the broader challenges in land administration and within the topic of 3D cadastral data are discussed.

Data validation in 3D cadastre

In a cadastre, the 2D parcel is nowadays correctly considered to be a special case of the 3D parcel because the rights and restrictions extend beyond the surface it-self. Storing, representing and manipulating a true 3D parcel however has not yet been satisfactorily achieved because of constraints in data modeling and soft-ware development. Significant research has been done to identify the best ways to represent a 3D solid, with rigorous mathematical testing on the respective merits of alternative approaches. Software companies have come up with their own ways of storing and validating 3D data, mostly as extensions of the 2D concepts. However, validation rules of one software may not be acceptable within another softwares validation environment. The validation itself can be specified in great detail but sometimes this leads to redundant, repetitive or unnecessary processing. Because of the high volume of data a typical organization may be expected to handle, it is necessary for the rules to be streamlined and efficient. In this paper, validation is initially approached to answer questions such as: what is validation? why it is necessary to validate?, and how do we validate?. Limiting the scope to the 3D geometry or spatial representation of a 3D cadastre, the paper takes a novel approach in identifying the various aspects of validation of a 3D cadastral parcel and identifies the critical validation factors. It examines the validity within individual parcels and the relationship between adjoining or overlapping parcels in 2D or 3D. Although it is difficult to ensure completeness of rules, critical validation rules are examined for each identified factor.