In the last decades, 3D city models appear to have been predominantly used for visualisation; however, today they are being increasingly employed in a number of domains and for a large range of tasks beyond visualisation. In this paper, we seek to understand and document the state of the art regarding the utilisation of 3D city models across multiple domains based on a comprehensive literature study including hundreds of research papers, technical reports and online resources. A challenge in a study such as ours is that the ways in which 3D city models are used cannot be readily listed due to fuzziness, terminological ambiguity, unclear added-value of 3D geoinformation in some instances, and absence of technical information. To address this challenge, we delineate a hierarchical terminology (spatial operations, use cases, applications), and develop a theoretical reasoning to segment and categorise the diverse uses of 3D city models. Following this framework, we provide a list of identified use cases of 3D city models (with a description of each), and their applications. Our study demonstrates that 3D city models are employed in at least 29 use cases that are a part of more than 100 applications. The classified inventory could be useful for scientists as well as stakeholders in the geospatial industry, such as companies and national mapping agencies, as it may serve as a reference document to better position their operations, design product portfolios, and to better understand the market.

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Applications of 3D City Models: State of the Art Review

Integrity is one criteria to evaluate GNSS performance, which was first introduced in the aviation field. It is a measure of trust which can be placed in the correctness of the information supplied by the total system. In recent years, many GNSS-based applications emerge in the urban environment including liability critical ones, so the concept of integrity attracts more and more attention from urban GNSS users. However, the algorithms developed for the aerospace domain cannot be introduced directly to the GNSS land applications. This is because a high data redundancy exists in the aviation domain and the hypothesis that only one failure occurs at a time is made, which is not the case for the urban users. The main objective of this paper is to provide an overview of the past and current literature discussing the GNSS integrity for urban transport applications so as to point out possible challenges faced by GNSS receivers in such scenario. Key differences between integrity monitoring scheme in aviation domain and urban transport field are addressed. And this paper also points out several open research issues in this field.

/pdf/gnss-position-integrity-in-urban-environments-a-review-of-1ved0w5512.pdf

GNSS Position Integrity in Urban Environments: A Review of Literature

Indoor location based services challenges, requirements and usability of current solutions

Multiple global navigation satellite system (GNSS) constellations can dramatically improve the signal availability in dense urban environments. However, accuracy remains a challenge because buildings block, reflect and diffract the signals. This paper investigates three different techniques for mitigating the impact of non-line-of-sight (NLOS) reception and multipath interference on position accuracy without using additional hardware, testing them using data collected at multiple sites in central London. Aiding the position solution using a terrain height database was found to have the biggest impact, improving the horizontal accuracy by 35% and the vertical accuracy by a factor of 4. An 8% improvement in horizontal accuracy was also obtained from weighting the GNSS measurements in the position solution according to the carrier-power-to-noise-density ratio (C/N0). Consistency checking using a conventional sequential elimination technique was found to degrade horizontal positioning performance by 60% because it often eliminated the wrong measurements in cases when multiple signals were affected by NLOS reception or strong multipath interference. A new consistency checking method that compares subsets of measurements performed better, but was still equally likely to improve or degrade the accuracy. This was partly because removing a poor measurement can result in adverse signal geometry, degrading the position accuracy. Based on this, several ways of improving the reliability of consistency checking are proposed.

/pdf/height-aiding-c-n-0-weighting-and-consistency-checking-for-mejz6ig1ar.pdf

Height Aiding, C/N 0 Weighting and Consistency Checking for GNSS NLOS and Multipath Mitigation in Urban Areas

The current low-cost global navigation satellite systems (GNSS) receiver cannot calculate satisfactory positioning results for pedestrian applications in urban areas with dense buildings due to multipath and non-line-of-sight effects. We develop a rectified positioning method using a basic three-dimensional city building model and ray-tracing simulation to mitigate the signal reflection effects. This proposed method is achieved by implementing a particle filter to distribute possible position candidates. The likelihood of each candidate is evaluated based on the similarity between the pseudorange measurement and simulated pseudorange of the candidate. Finally, the expectation of all the candidates is the rectified positioning of the proposed map method. The proposed method will serve as one sensor of an integrated system in the future. For this purpose, we successfully define a positioning accuracy based on the distribution of the candidates and their pseudorange similarity. The real data are recorded at an urban canyon environment in the Chiyoda district of Tokyo using a commercial grade u-blox GNSS receiver. Both static and dynamic tests were performed. With the aid of GLONASS and QZSS, it is shown that the proposed method can achieve a 4.4-m 1ź positioning error in the tested urban canyon area.

3D building model-based pedestrian positioning method using GPS/GLONASS/QZSS and its reliability calculation

Reliable metres-level positioning in dense urban areas is difficult to achieve cost-effectively using a single method The way forward is to combine multiple positioning techniques This paper introduces the concept of intelligent urban positioning (IUP), which combines ? Multi-constellation GNSS; ? Multiple techniques for detecting non-line-of-sight (NLOS) signal propagation; and ? Multiple techniques using three-dimensional mapping IUP may also be extended to incorporate other position-fixing and dead-reckoning sensors The paper begins by explaining the limitations of conventional GNSS positioning in dense urban environments It then introduces the potential ingredients of intelligent urban positioning, a mixture of new and established techniques, and discusses how they might be combined 3D mapping may be used for conventional map matching, height aiding, NLOS signal detection, reflection prediction and shadow matching, a new method for determining position by comparing measured and predicted satellite visibility NLOS reception may also be detected using consistency checking, C/N0 measurement, dual-polarization antenna technology, an antenna array and a sky-pointing camera The results of a preliminary demonstration of the IUP concept using GPS and GLONASS data collected in London are then presented In this test, conventional GNSS positioning, aided by consistency-based LOS detection is combined with shadow matching In the example presented, a horizontal position error of less than 2m was obtained, compared to about 25m for conventional GNSS positioning This clearly demonstrates the potential of the IUP approach Note, however, that further research is needed to improve the reliability

Intelligent Urban Positioning using Multi-Constellation GNSS with 3D Mapping and NLOS Signal Detection

The reception of indirect signals, either in the form of non-line-of-sight (NLOS) reception or multipath interference, is a major cause of GNSS position errors in urban environments. We explore the potential of using dual-polarisation antenna technology for detecting and mitigating the reception of NLOS signals and severe multipath interference. The new technique computes the value of the carrier-power-to-noise-density (C/N 0) measurements from left-hand circular polarised outputs subtracted from the right-hand circular polarised C/N 0 counterpart. If this quality is negative, NLOS signal reception is assumed. If the C/N 0 difference is positive, but falls below a threshold based on its lower bound in an open-sky environment, severe multipath interference is assumed. Results from two experiments are presented. Open-field testing was first performed to characterise the antenna behaviour and determine a suitable multipath detection threshold. The techniques were then tested in a dense urban area. Using the new method, two signals in the urban data were identified as NLOS-only reception during the occupation period at one station, while the majority of the remaining signals present were subject to a mixture of NLOS reception and severe multipath interference. The point positioning results were dramatically improved by excluding the detected NLOS measurements. The new technique is suited to a wide range of static ground applications based on our results.

/pdf/nlos-gps-signal-detection-using-a-dual-polarisation-antenna-5crkz1ompy.pdf

NLOS GPS signal detection using a dual-polarisation antenna

The next generation of navigation and positioning systems must provide greater accuracy and reliability in a range of challenging environments to meet the needs of a variety of mission-critical applications. No single navigation technology is robust enough to meet these requirements on its own, so a multisensor solution is required. Although many new navigation and positioning methods have been developed in recent years, little has been done to bring them together into a robust, reliable, and cost-effective integrated system. To achieve this, four key challenges must be met: complexity, context, ambiguity, and environmental data handling. This paper addresses each of these challenges. It describes the problems, discusses possible approaches, and proposes a program of research and standardization activities to solve them. The discussion is illustrated with results from research into urban GNSS positioning, GNSS shadow matching, environmental feature matching, and context detection.

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The four key challenges of advanced multisensor navigation and positioning

In a typical urban environment, a mixture of multipath-free,
multipath-contaminated and non-line-of-sight
(NLOS) propagated GNSS signals are received. The
errors caused by multipath-contaminated and NLOS
reception are the dominant source of reduced consumer-grade
positioning accuracy in the urban environment.
Many conventional receiver-based and antenna-based
techniques have been developed to mitigate either
multipath or NLOS reception with mixed success.
Nevertheless, the positioning accuracy can be maximised
based on the simple principle of selecting only those
signals least contaminated by multipath and NLOS
propagation to form the navigation solution. The advent
of multi-constellation GNSS provides the opportunity to
realise this technique that is potentially low-cost and
effective for consumer-grade devices. It may also be
implemented as an augmentation to other multipath
mitigation techniques.
The focus of this paper is signal selection by consistency
checking, whereby measurements from different satellites
are compared with each other to identify the NLOS and
most multipath-contaminated signals. The principle of
consistency checking is that multipath-contaminated and
NLOS measurements produce a less consistent navigation
solution than multipath-free measurements. RAIM-based
fault detection operates on the same principle.
Three consistency-checking schemes based on single-epoch
least-squares residuals are assessed: single sweep,
recursive checking and a hybrid version of the first two.
Two types of weighting schemes are also considered:
satellite elevation-based and signal C/N0-based weighting.
The paper also discussed the different observables that
may be used by a consistency-checking algorithm for
different applications and their effect on detection
sensitivity.
Test results for the proposed algorithms are presented
using data from both static positioning and stand-alone
dynamic positioning experiments. The static data was
collected using a pair of survey-grade multi-constellation
GNSS receivers using both GPS and GLONASS signals
at open sky and urban canyon locations, while the
dynamic data was collected using a consumer-grade
GPS/GLONASS receiver on a car in a mixed urban
environment. Significant improvements in position
domain are demonstrated using the weighted recursive
methods in the open environments. However in the urban
environments, there are insufficient directly received
signals for the conventional RAIM-based signal selection
to be effective all the time. Both positioning
improvements and risky outliers are demonstrated. More
advanced techniques have been identified for
investigation in future research.

https://discovery.ucl.ac.uk/1349795/1/3889.pdf

Ziyi Jiang

Papers

Height Aiding, C/N 0 Weighting and Consistency Checking for GNSS NLOS and Multipath Mitigation in Urban Areas

Intelligent Urban Positioning using Multi-Constellation GNSS with 3D Mapping and NLOS Signal Detection

NLOS GPS signal detection using a dual-polarisation antenna

The four key challenges of advanced multisensor navigation and positioning

Multi-Constellation GNSS Multipath Mitigation Using Consistency Checking