Point clouds contain high detail and high accuracy geometry representation of the scanned Earth surface parts. To manage the huge amount of data, the point clouds are traditionally organized on location and map-scale; e.g. in an octree structure, where top-levels of the tree contain few points suitable for small scale overviews and lower levels of the tree contain more points suitable for large scale detailed views. The drawback of this solution is that it is based on discrete levels, causing visual artifacts in the form of data density shocks when creating the commonly used perspective views. This paper presents a method based on an optimized distribution of points over continuous levels, avoiding the visualization shocks. The traditional distribution ratio's of data amounts over discrete levels of raster or vector data is considered the reference. How to convert this to point clouds with continuous levels (still benefiting from the proven advantages of the data distribution in discrete levels for efficient access at a wide range of scales)? In our solution, for each point a cLoD (continuous Level of Detail) value is computed and added as dimension to the point. A SFC (Space Filling Curve)-based nD data clustering technique can be used to organize the points, so that they can be efficiently queried. It should be noted that also other multi-dimensional indexing and clustering techniques could be applied to realize continuous levels based on the cLoD value. Besides the mathematical foundation of the approach also several implementations are described, varying from a 3D web-browser based solution to an augmented reality point cloud app in a mobile phone. The cLoD enables interactive real-time visualization using perspective views without data density shocks, while supporting continuous zoom-in/out and progressive data streaming between server and client. The described cLoD based approach is generic and supports different types of point clouds: from airborne, terrestrial, mobile and indoor laser scanning, but also from dense matching optical imagery or multi-beam echo soundings.

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As an extension to 2D polygonal queries, the nD-polytope queries on point clouds also play a crucial rolein nD GIS applications such as the perspective view selection. This report rst denes the nD-polytopemathematically, and then develops an ecient nD-polytope querying solution by extending an index-organized table (IOT) approach. The solution integrates four novel intersection algorithms includingCPLEX, SWEEP, SPHERE and VERTEX, each of which can be used to realize the primary lteringfor polytope querying. The performance of these algorithms is then measured and compared using anrepresentative nD-simplex and an nD-prism query region, respectively. It turns out that SWEEP performsthe best over all, but it may degrade signicantly as dimensionality goes up. On the other hand, thelinear programming algorithm CPLEX although takes more time on intersection computation, performsmore stable. Besides, the experiments also reveal that the properties of a same geometry can changesignicantly across dierent dimensionality, and thus optimal strategies developed in 2D/3D may not beapplicable in high dimensional spaces.@en

The prime purpose of Cadastral data – whether in the form of maps, survey plans or notes, or a digital database is the definitive demarcation of the extent of properties – and can be seen primarily as a decision support facility (“Can a structure be built here?”, “Where can I build a fence?”, “Should I buy this property”?). There are, however many additional uses for which this information has been applied – such as a base for the recording of assets such as light poles, underground cables, etc. and as a history of the pattern of land use and subdivision. Although secondary, these uses are important, and should be adequately supported including the historic information. It is a fact that the determination of cadastral boundaries can only be carried out to a certain accuracy, and that that accuracy has been improving over time. Older surveys had been carried out with limited positional control, and using equipment with a low intrinsic accuracy by modern standards, although they correctly represent the topology between properties. As a result, later surveys provide an opportunity to improve the positioning of existing boundaries data without disturbing the topology of the existing data. In addition, engineering works such as road building, can provide a source of high accuracy position data that can be applied to improve low accuracy existing data. This argues that the accuracy of boundaries should be improved in the historic record of the cadastre – after all we would like to see our historic parcels in the position we now know them to have been, so that they are comparable with current boundaries. Likewise, we need to correct inaccuracies in the attributes of the spatial objects and the topology between them (e.g. which spatial units are adjacent to or near a given object). On the other hand, we must not lose sight of the decision-making side of the requirements – so that a past decision can be reviewed in relation to the data as it existed then. If the current knowledge in the database of today is used to review old decisions, they may seem irrational. Data custodians are well aware of this issue, using terms like “update” to indicate a “real-world” change, while using “upgrade” to indicate an improvement of the database representation not accompanied with a change “on the ground”; however database software has not carried this knowledge through – resulting in its loss. This argues for a database with bi-temporal history – where our current best knowledge of the history of the cadastre is recorded, and that history is corrected and maintained, while our past knowledge of the data also recorded as an audit trail (so that we can ask questions like “what did we in 2017 think the definition of this property was in 1994?”). This is realized via two types of time: database (or system) time and real world (or valid) time. The different historic records, combined with changes of datum, can lead to confusion in terminology – where words such as “point”, “position”, “boundary” become overloaded. This paper is intended to provoke discussion of terminology to clear up this confusion, and potentially to assist with an extension of the temporal model as input for the revision of LADM to accommodate bi-temporality.

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Efficient spatial queries are frequently needed to extract useful information from massive nD point clouds. Most previous studies focus on developing solutions for orthogonal window queries, while rarely considering the polytope query. The latter query, which includes the widely adopted polygonal query in 2D, also plays a critical role in many nD spatial applications such as the perspective view selection. Aiming for an nD solution, this paper first formulates a convex nD-polytope for querying. Then, the paper integrates three approximate geometric algorithms – SWEEP, SPHERE, VERTEX, and a linear programming method CPLEX, developing a solution based on an Index-Organized Table (IOT) approach. IOT is applied with space filling curve based clustering and advanced querying mechanism which recursively refines hypercubic nD spaces to approach the query geometry for primary filtering. Results from experiments based on both synthetic and real data have confirmed the superior performance of SWEEP. However, the algorithm may lag behind CPLEX due to pessimistic intersection computation in high dimensional spaces. In a real application, by properly transforming a perspective view selection into a polytope query, the solution achieves a sub-second querying performance using SWEEP. In another flood risk query, SWEEP also leads the others. In general, the robust and efficient solution can be immediately used to address different polytope queries, including those abstract ones whose constraints on combinations of different dimensions are formed into a polytope model. Besides, the knowledge of high-dimensional computations acquired also provides significant guidance for handling more nD GIS issues.

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This paper describes research into the design, development and visualization of mixed 2D and 3D Cadastre. A schema has been developed to accommodate this data, with provision for a time component. This paper describes the schema, the visualization requirements, and the provision of LADM-compatible views of the data for the purpose of developing the 3D Cadastral prototype. A significant volume of 2D + t Cadastral data, which also contained 2D + t footprint representations of 3D parcels, is currently incorporated in the Cadastral Database of Queensland. A moderate number of 3D building units, and a smaller number of volumetric parcels have been hand-encoded (from the survey plans), and added to this database. The mixture has been disseminated and displayed in KML through Cesium JS. The visualization of cadastral parcels in 3D is a challenge, since legal boundaries are, in many cases, invisible in the real world; so how can we properly represent something that is not visible to our eyes? This paper uses the results from research looking into problems of occlusion and ambiguous perception (in terms of position, size and shape) of objects in the context of 3D cadastre visualization. The exploration of specific interaction techniques is essential to overcome these issues. After an initial internal usability test (with colleagues/ friends of the developers) our 3D Cadastres web-based dissemination prototype was improved. Next a public usability test is carried out to obtain feedback from different groups of professional users (legal, survey, ICT backgrounds). During the test, the users are asked to perform a series of tasks typical of cadastral systems. Each task is accompanied by a description to give the users some context. Then, each user is asked to reflect on his or her experience. In this paper we present the main results of the public usability test of the 3D Cadastres web-based dissemination prototype.

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Cadastral databases have unique requirements not shared by other spatial databases: The third spatial dimension must be included, but visualisation using 2D software must also be accommodated. The majority of users of the Cadastre will use 2D software, and should be provided an “instant in time” plan view of the boundaries (with any 3D parcels “flattened”). Some users will have access to and need for fully functioned 3D software, and some to tools with “time sliders” but access to the Cadastre cannot be restricted to such users. A history of the Cadastre must be maintained. It is important that patterns of subdivision and land use can be tracked through the past, and it is highly desirable that planned future activity is included. In addition, a record of the state of knowledge of the database is needed (in case past decisions must be reviewed). That is to say, both the “valid time” and “transaction time” forms of time stamping needs to be accommodated. The accuracy of the data is constantly being improved (each time a new survey is done), and this action must be reflected within the database as it becomes available. Other parties traditionally use the Cadastral database as a “base map”, and accuracy improvements need to be promulgated to these parties. This paper builds on previous research and development – mixing 2D and 3D cadastre has already been demonstrated, as has Cadastre with transaction time history. This paper considers what is needed to complete the schema. Specifically: The storage of real-world (valid time) history. The storage of “tentative time” temporal data for proposed developments. Database (transaction) time, supported by versioning. The improvement of accuracy of Cadastral boundaries, both in 2D and 3D spatial units, and of historic spatial units. 2D and 3D views of the data, and 2D update of the data. Making the data available in scalable services, including access to historic items, and update history. The novelty of this research is the combination of the full 4D/5D functionality in a single schema that can be implemented in a practical multi-user Cadastral database. This is the first time such a rigorous solution has been presented.@en

The prime purpose of Cadastral data – whether in the form of maps, survey plans or notes, or a digital database is the definitive demarcation of the extent of properties – and can be seen primarily as a decision support facility (“Can a structure be built here?”, “Where can I build a fence?”, “Should I buy this property”?). There are, however many additional uses for which this information has been applied – such as a base for the recording of assets such as light poles, underground cables, etc. and as a history of the pattern of land use and subdivision. Although secondary, these uses are important, and should be adequately supported.@en

The visualization of cadastral parcels in 3D is a challenge, since legal boundaries are, in many cases, invisible in the real world; so how can we properly represent something that is not visible to our eyes? This paper uses the results from research looking into problems of occlusion and ambiguous perception (in terms of position, size and shape) of objects in the context of 3D cadastre visualization. The exploration of specific interaction techniques is essential to overcome these issues. After an initial internal usability test (with colleagues/ friends of the developers) our 3D Cadastres web-based dissemination prototype was improved. Next a public usability test is carried out to obtain feedback from different groups of professional users (legal, survey, ICT backgrounds). Usability is meant in terms of effectiveness and efficiency of the system and users' satisfaction. The test users were subdivided into groups according to different professional domains and expertise. During the test, the users are asked to perform a series of tasks typical of cadastral systems. Each task is accompanied by a description to give the users some context. Then, each user is asked to answer a questionnaire about his or her experience. The results are used to extract general feedback. The outcome of the usability test is crucial to point out the detected limitations in this early stage of the prototype development. Design changes can then be made according to the feedback of the test users. In this paper we present the main results of the public usability test of the 3D Cadastres web-based dissemination prototype.@en

More and more countries in the world are developing 3D Cadastre. To make cadastral information available to the potential users, both cadastral sector professionals and normal citizens, the Web can be used as dissemination platform. However, visualization of 3D cadastral information is still a challenge. Some of the main issues are: occlusion, distortion, unbounded volumes, perception of position, size and shape of an object. For orientation purposes, it is important to include reference objects to help us understand the location of the parcels in the real world. Although, the resulting higher number of objects makes the clear visualization even more challenging. We therefore first investigate the requirements to obtain a proper, clear and not misleading visualisation of 3D cadastral parcels through a geo-web viewer. We explore how to handle the above-mentioned issues such as occlusion, distortion and ambiguous perception (in terms of position, size and shape) of objects while interacting with 3D cadastre. Also, techniques for combining the visualization of legal boundaries (cadastral parcels) and real-world objects (topography) are analysed. The overall technical architecture of a system for the dissemination 3D Cadastral parcels is presented, starting with the storage of the data at the backend server (DBMS and webserver) and the possible encodings for data transfer (such as XML, JSON, glTF) to the client. WebGL based solutions at client side are preferred as these do not require the download of a plugin in the web browser, while still offering many well performing visualization and interaction options.@en

This paper describes research into the visualization of mixed 2D and 3D Cadastre. A schema has been developed to accommodate this data, with provision for a time component. This paper describes the schema, the visualization requirements, and the provision of LADMcompatible views of the data for the purpose of developing these tools, and for the further research into the schema itself. A significant volume of 2D+t Cadastral data, which also contained 2D+t representations of 3D parcels, is currently incorporated in the Cadastral Database of Queensland. A moderate number of 3D building units, and a smaller number of volumetric parcels have been hand-encoded using bespoke software, and added to this database. The mixture has been displayed in KML through Google Earth. Examples of the database schemas, the encoding practices, LADM-compatible views, and the encoded 2 and 3 dimensional spatial units are included.@en

Dense urbanisation has led to an increasing demand and pressure for land development, resulting in the partition of 3D space into different owners sharing delimited property interests on, above or below the land surface. Consequently, cadastral spatial units range from simple, but most common, 2D, to complex 3D collections of spaces worldwide, that are more difficult to handle in terms of surveying, storing in a database, maintaining, visualising, etc. Subsequently, this asks for the categorization and organization of the different types of spatial units that are physically identified and legally recognised in various jurisdictions worldwide. In the context of the Land Administration Domain Model (LADM) (ISO 19152, 2012), the “level” concept (LA_Level class) provides a framework for organising the different types of spatial units. Based on that, five levels of encoding are defined in ISO19152, providing a framework of categorisation of 2D spatial units, represented by five spatial profiles included in Annex E of ISO 19152. Six years after the publication of the first edition of LADM as ISO standard, a lot of research has been carried out by experts from all over the world, and today, the ground seems to be mature for the LADM (edition I) revision, which started in May 2018, as a joint activity with many stakeholders involved (ISO TC211, OGC, FIG, etc.). One of the goals of the revision, among others, is to improve LADM’s current 3D support. This can be achieved through the design of new 3D spatial profiles for the different types of spatial units that are recognised by cadastral authorities in various jurisdictions. New and different 3D spatial units’ types may be considered for inclusion in the standard. To this end, the aim of this paper is to investigate, examine and review - in the context of LADM revision- the different types of real-world spatial units, as they have initially been organised by Thompson et al (2015). Based on the revised taxonomy, spatial profiles for the spatial units’ categories are introduced and (several) are further explored and designed. Hence, the focus on this paper lies on two levels: the taxonomy and the spatial profiles, while the level of encoding is not included in the scope of this paper. However, the investigation of the technical encodings that will be used for the implementation of the 3D spatial profiles is introduced at the paper as future work, underlying its importance. Within this concept, the scope and ambition of LADM revision are discussed.@en

In this chapter we address various aspects of 3D Cadastral Information Modelling. Of course, this is closely related to the legal framework and initial registration as presented in the first two chapters. Cadastral data models, such as the Land Administration Domain Model, which include 3D support, have been developed for legal information modelling and management purposes without providing correspondence to the object’s physical counterparts. Building Information Models and virtual 3D topographic/ city models (e.g. LandXML, InfraGML, CityGML, IndoorGML) can be used to describe the physical reality. The main focus of such models is on the physical and functional characteristics of urban structures (Aien et al, 2015). However, by definition, those two aspects need to be interrelated; i.e. a tunnel, a building, a mine, etc. always have both a legal status and boundaries as well as a physical description; while it is evident that their integration would maximise their utility and flexibility to support different applications. A model driven architecture approach, including the formalization of constraints is preferred. In the model driven architecture design approach as proposed by the Object Management Group the information model, often expressed in the form of a UML class diagram is the core of the development. This so-called Platform Independent Model (PIM, as presented in the current chapter) is then transformed into Platform Specific Model (PSM). This could be a relational database schema for a spatial DBMS (as will be discussed in the next chapter), or XML schema for a data exchange format or the structure of maps, forms and tables as used in the graphic user interface of a spatial application. Constraints have proved effective in providing the solutions needed to avoid errors and enable maintenance of data quality; thus the need to specify and implement them. This chapter explores possibilities of linking 3D legal right, restriction, responsibilities spaces, modelled with the Land Administration Domain Model (ISO 19152), with physical reality of 3D objects (described via CityGML, IFC, InfraGML, etc).@en

Many countries are extending their cadastral visualization systems in the third dimension. The reason for this stems from the increasing complexity of contemporary cities, the growing 3D approach in other fields (including 3D spatial data acquisition, spatial data processing and visualization), which made 3D cadastre technologically feasible, and the need to overcome the issues of 2D visualization. The visualization of cadastral parcels in 3D is a challenge, since legal boundaries are, in many cases, invisible in the real world; so how can we properly represent something that is not visible to our eyes? This paper results from research that looks into problems of occlusion and ambiguous perception (in terms of position, size and shape) of objects in the context of 3D cadastre visualization. The exploration of specific interaction techniques is essential to overcome these issues. The aim of this paper is to provide ’lessons learned’ resulting from the implementation of a 3D cadastre prototype that was built with the specific goal of trying out several visualization options of 3D cadastral information in a web environment. A usability test was carried out to obtain feedback from different groups of users. Usability is meant in terms of effectiveness and efficiency of the system and users’ satisfaction. The test users were subdivided into groups according to different professional domains and expertise. During the test, the users are asked to perform a series of tasks typical of cadastral systems. Each task is accompanied by a description to give the users some context. Then, each user is asked to answer a questionnaire about his or her experience. The results are used to extract general feedback. The outcome of the usability test is crucial to point out the detected limitations in this early stage of the prototype development. Design changes can then be made according to the feedback of the test users.@en

Cadastral spatial units around the world range from simple 2D parcels to complex 3D collections of spaces, defined at levels of sophistication from textural descriptions to complete, rigorous mathematical descriptions based on measurements and coordinates. The most common spatial unit in a cadastral database is the 2D land parcel-the basic unit subject to cadastral Rights, Restrictions and Responsibilities (RRR). Built on this is a varying complexity of 3D subdivisions and secondary interests. Spatial units may also be subdivided into smaller units, with the remainder being kept as common property for the owners/tenants of the individual units. This has led to the adoption of hierarchical multi-level schemes. In this paper, we explore the encoding of spatial units in a way that highlights their 2D extent and topology, while fully defining their extent in the third dimension. Obviously, topological encoding itself is not new. However, having mixed a 2D and 3D topological structure is rather challenging. Therefore, despite the potential benefits of mixed 2D and 3D topology, it is currently not used in LandXML, one of the main and best documented formats when representing survey data. This paper presents a multi-level topological encoding for the purposes of survey plan representation in LandXML that is simple and efficient in space requirements, including the question of curved surfaces, (partly) unbounded spatial units, and grouping and division of 2D and 3D spatial units. No off the shelf software is available for validating newly lodged surveys and we present our prototype for this. It is further suggested that the conceptual model behind this encoding approach can be extend to the database schema itself.

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