Modelling and extracting 3D geographical data presents numerous challenges that require continual research to attempt to evolve an efficient, reliable and accurate solution. LiDAR data capture and analysis has become a preferred acquisition choice for elevation data because the resulting quality and level of detail far exceeds traditional methods for large survey areas. As with any data collection system, LiDAR is prone to errors. Analysing these errors, ascertaining causes and producing error correction strategies is vital if accurate and confident results are to be obtained. Eight years of LiDAR datasets (from 1998 to 2005) have been closely analysed for a large coastal area of South Wales. This article provides a detailed and accurate summary of the identified LiDAR data issues and subsequent errors which affect the accuracy of end products such as Digital Surface Models (DSMs).

Maintenance of a multiple representation GIS using data from a variety of sources at differing scales requires update processing that can recognise equivalences and differences between new data and stored representations. Factors that may be taken into account when establishing equivalence and difference include a) measures of similarity of the location of new and stored geometry, having regard to positional error; b) comparison of classification and names ; and c) comparison of geometric shape parameters . Decisions about update of representations of equivalent real-world phenomena may depend upon the capabilities of automatic generalisation procedures that could be used to derive one scale of representation from another. Access to data at different levels of detail, for answering queries and for processing updates, is facilitated by the use of multiresolution data structures .

This paper explains a ray tracing method which is applied to prediction and visualization of diffracted and reflected GPS signals in dense urban areas. Reflected and diffracted signals can have a detrimental effect on GPS positioning accuracy especially in highly built‐up areas. The ray tracing technique implemented in this paper is specially geared to LiDAR height pole data at 1‐m spatial resolution and 2D building footprints in raster and vector format, respectively. Such a simple data format allows for rapid implementation of 3D ray tracing in a GIS without further processing so that detailed 3D urban models in vector format are not required. Issues of spatial uncertainty in the data used are also addressed in relation to the identification of multipath signals. Some preliminary results obtained from fieldwork are presented and analysed in detail.

This paper describes an automated method for predicting the number of satellites visible to a GPS receiver, at any point on the Earth's surface at any time. Intervisibility analysis between a GPS receiver and each potentially visible GPS satellite is performed using a number of different surface models and satellite orbit calculations. The developed software can work with various ephemeris data, and will compute satellite visibility in real time. Real-time satellite availability prediction is very useful for mobile applications such as in-car navigation systems, personal navigations systems and LBS. The implementation of the method is described and the results are reported.

This paper aims to investigate how 1m LiDAR data and 2D building footprints can be used to predict GPS multipath effects in urban areas. A ray tracing model is implemented in order to model reflected and diffracted GPS signals. Some preliminary results are presented and explained in detail.

This paper describes an automated method for predicting the number of satellites visible to a GPS receiver, at any point on the earth’s surface at any time. Intervisibility analysis between a GPS receiver and each potentially visible GPS satellite are performed using a number of different surface models and satellite orbit calculations. The developed software can work with various ephemeris data, and will compute satellite visibility in real-time. Real-time satellite availability prediction is very useful for mobile applications such as in-car navigation systems, personal navigations systems and LBS. The implement- tation of the method is described and the results are reported.

This paper presents a case study of one of United Kingdom's largest brewing group's experience with computerized vehicle routing and scheduling (CVRS) system. The study clearly illustrates that the use of commercial CVRS software is an effective means of reducing freight transport costs. The savings identified in this research confirm the findings of previous studies on CVRS which have revealed savings to usually in the range from 5 to 15% of a company's transport costs. In addition to direct cost savings, CVRS also yields substantial qualitative benefits which ultimately may result in significant cost savings or increase sales. Special emphasis needs to be placed on the proper management of human factors. The implementation measures should aim to gain the acceptance of the relevant personnel and their union representatives for the change from manual to computerized planning, facilitating the smooth integration of the software into existing work procedure and providing training of the system operators.

Visibility analysis is now a key function of many geographical information systems. It is also one of the most contentious tools, as it is notoriously prone to error. The paper will demonstrate the versatility of the Multiscale Implicit Triangulated Irregular Network (TIN) for the application of intervisibility analysis at multiple resolutions. This approach allows for the integration of three‐dimensional (3D) topographic features with the terrain surface. The multiscale TINs are derived from generalising digital contours at a variety of lateral tolerances. The models' performances are evaluated from an extensive field study undertaken in the South Wales valleys. Results suggest that the accuracy of intervisibility analysis is very dependent upon the availability of good quality 3D topographic data. In our study, such data were shown to improve visibility performance by more than 44% over its bare‐earth TIN equivalent. Interestingly, generalisation of the TINs had very little effect on visibility performance. In addition, a Monte Carlo approach to sensitivity analysis was found to be detrimental to the accuracy of visibility prediction in the full terrain and topographic models. However, this probable approach can improve intervisibility performance by up to 18% on a bare‐earth TIN. The range of these visibility modelling scenarios demonstrate the flexibility of the Multiscale Implicit TIN for digital surface modelling.

The Multiscale Implicit Triangulated Irregular Network (TIN) provides a storage and access scheme for generating triangulated terrain models that adapt their content and level of detail to the requirements of the user. The scheme combines storage of data representing the terrain surface, and two and three dimensional terrain features, with a retrieval and triangulation procedure that generates a constrained Delaunay triangulation at run time. The feature content and level of detail may be specified by the user, thereby providing a flexible facility that adapts to the requirements of a wide range of applications, whether global or local, exploratory or precise. This paper provides an overview of the scheme and illustrates its application for a variety of queries requiring multiscale representations.

1. ABSTRACT The paper describes a number of distributed approaches to implementing a parallel vklbility a]g~rithm for Viewshed analysis. The problem can be simplified by considering a range of domain partitioning strategies for optimizing tie proc=sor worldoads. The best approaches are shown to work 22 times faster across a network of 24 processors. Such strategies allow traditional GIS functionality to be extended into new problem areas or to higher resolution spatial data using existing computing resources. Ke~~vords Intervisilility and viewshed analysis, digital terrain modeliig, DEhL parallel computing, distributed computing

The application of parallel processing to computationally intensive GISproblems has been advocated and illustrated by many researchers over thelast twenty years. Despite this, GIS users have been slow to capitalize onthe potential which the technology offers. Whilst today’s processorsare adequate for the majority of GIS uses, some applications are tooprocessor-intensive to be deemed viable for serial machines. This isparticularly true of many digital terrain modelling applications, which hasbeen the primary focus of parallel processing in GIS to date. This paperconsiders the problem of parallelizing line-of-sight (LOS) calculations indetermining the visibility indices of entities such as elevation vertices ina digital terrain model (DTM). This is a requirement of site selection for aparticular development, especially if visibility, or more specifically,visual intrusion is likely to be a key factor in gaining planning approval.To demonstrate the simplicity and applicability of parallelizing such GISproblems, this paper presents some parallel approaches in an efficient dataorganization, framework using a Transputer network. Speed-up performance canbe increased by a factor of twelve using a simple network of twentyTransputers. As vast quantities of spatial data become available,particularly DTMs at larger scales and denser resolution, the demands forparallel processing will inevitably increase. It is hoped that the continuedexperiences of today’s researchers at applying parallel processing towell-defined problems will benefit the GIS users of tomorrow.

Presents an in‐depth case study of the practical experience of applying interactive vehicle routeing and scheduling software at a major brewing company in the United Kingdom (UK). Illustrates the use of the software at all levels of transport planning and addresses strategic, tactical and operational issues; comprises a review of the software′s overall implementation and its consequences within the organization. Special attention is given to the critical analysis of both quantitative and qualitative benefits, as well as organizational problems arising from the use of such software.

The Multiscale Implicit Triangulated Irregular Network (TIN) provides a storage and access scheme for generating triangulated terrain models that adapt their content and level of detail to the requirements of the user. The scheme combines storage of data representing the terrain surface, and two and three dimensional terrain features, with a retrieval and triangulation procedure that generates a constrained Delaunay triangulation at run time. The feature content and level of detail may be specified by the user, thereby providing a flexible facility that adapts to the requirements of a wide range of applications, whether global or local, exploratory or precise. This paper provides an overview of the scheme and illustrates its application for a variety of queries requiring multiscale representations.