Using building and bridge information for adapting roads to ALS data by means of network snakes

In the German Authoritative Topographic Cartographic Information System (ATKIS), the 2D positions and the heights of objects such as roads are stored separately in the digital landscape model (DLM) and digital terrain model (DTM), which is often acquired by airborne laser scanning (ALS). However, an increasing number of applications require a combined processing and visualization of these two data sets. Due to different kinds of acquisition, processing, and modelling discrepancies exist between the DTM and DLM and thus a simple integration may lead to semantically incorrect 3D objects. For example, roads may be situated on strongly tilted DTM parts and rivers sometimes flow uphill. In this paper we propose an algorithm for the adaptation of 2D road centrelines to ALS data by means of network snakes. Generally, the image energy for the snakes is defined based on ALS intensity and height information and derived products. Additionally, buildings and bridges as strong features in height data are exploited in order to support the road adaptation process. Extracted buildings as priors modified by a distance transform are used to create a force of repulsion for the road vectors integrated in the image energy. In contrast, bridges give strong evidence for the correct road position in the height data. Therefore, the image energy is adapted for the bridge points. For that purpose bridge detection in the DTM is performed starting from an approximate position using template matching. Examples are given which apply the concept of network-snakes with new image energy for the adaptation of road networks to ALS data taking advantage of the prior known topology

Constraint energies for the adaptation of 2d river borderlines to airborne laserscanning data using snakes

The German Authoritative Topographic Cartographic Information System (ATKIS) stores the height and the 2D position of the objects in a dual system. The digital terrain model (DTM), often acquired by airborne laser scanning (ALS), supplies the height information in a regular grid, whereas 2D vector data are provided in the digital landscape model (DLM). However, an increasing number of applications, such as flood risk modelling, require the combined processing and visualization of these two data sets. Due to different kinds of acquisition, processing, and modelling discrepancies exist between the DTM and DLM and thus a simple integration may lead to semantically incorrect 3D objects. For example, rivers may flow uphill. In this paper we propose an algorithm for the adaptation of 2D river borderlines to ALS data by means of snakes. Besides the two basic energy terms of the snake, the internal and image energy, 3D object knowledge is introduced in the constraint energy in order to guarantee the semantic correctness of the rivers in a combined data set. The image energy is based on ALS intensity and height information and derived products. Additionally, features of rivers in the DTM, such as the flow direction or the river profile, are formulated as constraints in order to fulfil the semantic properties of rivers and stabilize the adaptation process. Furthermore, the known concept of twin snakes exploits the width of the river and also supports the procedure. Some results are given to show the applicability of the algorithm

Snakes for adapting GIS road and river objects to airborne laser scanning data

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DEFINITION OF A TRANSITION SURFACE WITH THE PURPOSE OF INTEGRATION BETWEEN A LASER SCANNER 3D MODEL AND A LOW RESOLUTION DTM

ABSTRACT: Thanks to quickly spreading technologies like laser scanning, which are becoming a quite common means of data acquisition for architectural objects or cultural heritage sites (but not only!), integration between datasets of different origin and resolution is still an open problem. This paper describes an approach whose goal is to define a surface which models a proper transition between a high resolution, laser-scanner-acquired model and a low resolution digital terrain model (DTM), by means of some "extra" information around the high resolution object as sort of "collar". This information is generally present in laser scanner models and instead of pruning it during point cloud editing, we use it for our modelling purposes. We present a (so far) deterministic approach, some initial results and discuss still unresolved issues and future improvements. KURZFASSUNG: Dank der schnellen Verbreitung von Technologien wie z.B. Laser-Scannen, die zur Vermessung architektonischer Objekte oder Kulturgüter immer häufiger Anwendung finden, bleibt die Integration von Datensätzen unterschiedlichen Ursprungs und verschiedener Auflösung ein noch ungelöstes Problem. In diesem Artikel wird ein Ansatz beschrieben, dessen Ziel die Definition einer Übergangsfläche zwischen einem hoch aufgelösten, durch Laser-Scanner aufgenommenen Model und einem gröberen digitalen Geländemodell (DGM) ist, indem einige zusätzliche Informationen um das hoch aufgelöste Objekt so wie ein "Kragen" verwendet werden. Diese weiteren Daten sind im Allgemeinen in den Laser-Scanner-Datensätzen bereits vorhanden und werden hiermit zum Zweck der Oberflächenmodellierung genutzt, statt -wie sonst üblich -in der Editierungsphase eliminiert zu werden. Ein deterministischer Ansatz wird, zusammen mit den ersten Test-Ergebnissen, vorgestellt. Offene Probleme und künftige Aufbesserungen werden angesprochen

Spatial coincidence modelling, automated database updating and data consistency in vector GIS

This thesis presents formal approaches for automated database updating and consistency control in vector- structured spatial databases. To serve as a framework, a conceptual data model is formalized for the representation of geo-data from multiple map layers in which a map layer denotes a set of terrain objects of the same mapping context, e.g., cadastral, soil mapping, etc. The necessity for a generalised model arises from the frequent requirement in spatial analysis and planning for a geometric integration of several different views of the world, whereas most existing data models were designed from the perspective of a "single application" leading to ad hoc and repeated overlay computations (during query processing) when dealing with an integrated analysis. An alternative model is therefore proposed in this thesis for the geometric integration of geo-data from multiple map layers. The proposed model is an object-based, query-oriented 2.5D data model for multi-valued vector maps (DMMVM).A multi-valued vector map refers to the vector-based representation of terrain objects from multiple map layers whereby two objects of the same geometric type may be spatially coincident. Two objects of the same type are spatially coincident if they (partially) overlap in space. In this model, positions of objects are defined in a 3D metric space but embedded in 2D topologic space. The model is based on the 2D formal data structure (FDS) for singlevalued vector maps.Terrain objects play a central role in the terrain description; each object has a thematic component and a geometric component. In the thematic domain, the objects can be grouped into thematic classes in which each class has a specific attribute structure, and in the geometric domain the object types (points, lines and areas) are distinguished for a 2D or 2.5D terrain description.A geometric data type -- the m-dimensional container, or simply m-container, where m ε{0,1,2} -- is then introduced to model spatial coincidence among objects of the same geometric type. By introducing the container data type, overlapping sections across the layers are uniquely identified such that they have their own individual geometric data and nonspatial data, apart from those inherited from the overlapping objects; they can then be maintained and manipulated by the DBMS just like single objects. Using graph theory as a mathematical tool, the three container types are then represented by the topologic primitives arc and node. A node defines one 0-container andlor the beginning or end of an arc, while an arc defines (part of) one 1-container andlor (part of) the boundary of a 2-container. The arc is defined by one start node and one end node, and a node is defined by a coordinate triplet X,Y,Z. A flexible integration of the model with a DTM is also presented in the thesis, using an edge-based TIN. Two primitives of the edge-based TIN (edge and vertex) are added to the data types of the DMMVM to define the integrated model.Research and development on the updating of geo-information have been confined mainly to the aspects of data collection and change detection, with little emphasis on the corresponding automated propagation of the updating in the database in a consistent manner. To address the latter aspect, procedures are formulated in the thesis for a consistent automated updating of a vector-structured database, using the DMMVM as a framework. Algorithms are provided for the automated update propagation such that topology is automatically updated by the system, while maintaining structural and semantic consistency. This will improve on the current practice in operational systems, which usually requires a delayed reconstruction of topology whenever there is a geometric change in the database. Algorithms are developed for the insertion, deletion or modification of each of the eight data types (area, line, point, 2- container, 1-container, 0-container, arc and node) in the DMMVM. The human operator interacts with the system at the object-level, while the system propagates the update. The topology of the database is updated dynamically by the system by evaluating, using computational geometry, the topologic relationship between the new primitive (are or node) of an object and the existing primitives in the database. The type of relationship detected will then activate the relevant consistency rule (including update propagation) to validate the topology and consistency of the database. The system alerts the human operator if it is not possible for it to resolve the inconsistency.To enforce data consistency during geometric updating of the database, consistency rules are defined to ensure structural consistency, while a monitoring strategy is formulated for semantic (application-dependent, topologic) constraints. In both cases, topology plays the central role as an "alerter" of constraint violations. Thus the possible topologic relationships among the three elementary object types (area, line and point), and among the geometric primitives (arc and node) in the DMMVM are formalised and algorithms are defined for detecting the occurrence of any of the elementary relationships for any object combination. Then the consistency constraints can be translated to topologic relationships and stored in the database as events, and the corresponding responses of the system to enforce consistency can be defined as actions, thus giving a rule-based procedure (using the if event then action convention) for the management of data consistency in spatial databases.The DMMVM was translated into a relational database structure and an object-oriented database structure to facilitate implementation in a variety of systems. The object-oriented data structure and the consistency rules and algorithms were tested experimentally using Postgres, an extended relational database management system. Data were acquired using the Kork digital mapping system, on a Planicomp C120 photogrammetric stereoplotter equipped with a Zeiss Videomap and a Calcomp drawing board digitizer.The thesis concludes with an evaluation of the proposed model and an outline of areas requiring further investigations

Archaeological 3D GIS

Archaeological 3D GIS provides archaeologists with a guide to explore and understand the unprecedented opportunities for collecting, visualising, and analysing archaeological datasets in three dimensions. With platforms allowing archaeologists to link, query, and analyse in a virtual, georeferenced space information collected by different specialists, the book highlights how it is possible to re-think aspects of theory and practice which relate to GIS. It explores which questions can be addressed in such a new environment and how they are going to impact the way we interpret the past. By using material from several international case studies such as Pompeii, Çatalhöyük, as well as prehistoric and protohistoric sites in Southern Scandinavia, this book discusses the use of the third dimension in support of archaeological practice. This book will be essential for researchers and scholars who focus on archaeology and spatial analysis, and is designed and structured to serve as a textbook for GIS and digital archaeology courses

Archaeological 3D GIS

Archaeological 3D GIS provides archaeologists with a guide to explore and understand the unprecedented opportunities for collecting, visualising, and analysing archaeological datasets in three dimensions. With platforms allowing archaeologists to link, query, and analyse in a virtual, georeferenced space information collected by different specialists, the book highlights how it is possible to re-think aspects of theory and practice which relate to GIS. It explores which questions can be addressed in such a new environment and how they are going to impact the way we interpret the past. By using material from several international case studies such as Pompeii, Çatalhöyük, as well as prehistoric and protohistoric sites in Southern Scandinavia, this book discusses the use of the third dimension in support of archaeological practice. This book will be essential for researchers and scholars who focus on archaeology and spatial analysis, and is designed and structured to serve as a textbook for GIS and digital archaeology courses

Archaeological 3D GIS

"Archaeological 3D GIS provides archaeologists with a guide to explore and understand the unprecedented opportunities for collecting, visualising, and analysing archaeological datasets in three dimensions. With platforms allowing archaeologists to link, query, and analyse in a virtual, georeferenced space information collected by different specialists, the book highlights how it is possible to re-think aspects of theory and practice which relate to GIS. It explores which questions can be addressed in such a new environment and how they are going to impact the way we interpret the past. By using material from several international case studies such as Pompeii, Çatalhöyük, as well as prehistoric and protohistoric sites in Southern Scandinavia, this book discusses the use of the third dimension in support of archaeological practice. This book will be essential for researchers and scholars who focus on archaeology and spatial analysis, and is designed and structured to serve as a textbook for GIS and digital archaeology courses.