M. J. Smith

Adaptive Kalman filtering algorithms for integrating GPS and low cost INS

GPS and Inertial Navigation Systems are used for positioning and attitude determination in a wide range of applications. Over the last few years, a number of low cost inertial sensors have become available. Although they exhibit large errors, GPS measurements can be used correct the INS and sensor errors to provide high accuracy real-time navigation. The integration of GPS and INS measurements is usually achieved using a Kalman filter. The measurement and process noise matrices used in the Kalman filter represent the stochastic properties of the GPS and INS systems respectively. Traditionally they are defined a priori and remain constant throughout a processing run. In reality, the stochastic properties of the system vary depending on factors such as vehicle dynamics and environmental conditions. This is particularly an issue for low cost inertial sensors where the initial sensor errors can be large, and experience significant temporal variation. This paper investigates three adaptive Kalman filtering algorithms that can be used to improve the estimation of the stochastic properties of a low cost INS. The algorithms are tested using a low cost Crossbow MEMS IMU integrated with carrier phase GPS for a marine application. The adaptive Kalman filtering algorithms are shown to reduce the dependence on the a priori information used in the filter. This results in a reduction in the time required to initialise the sensor errors and align the INS, and results in an improvement in navigation performance.

Activity profiles of elite wheelchair rugby players during competition.

PURPOSE To quantify the activity profiles of elite wheelchair rugby (WCR) players and establish classification-specific arbitrary speed zones. In addition, indicators of fatigue during full matches were explored. METHODS Seventy-five elite WCR players from 11 national teams were monitored using a radio-frequency-based, indoor tracking system across 2 international tournaments. Players who participated in complete quarters (n = 75) and full matches (n = 25) were included and grouped by their International Wheelchair Rugby Federation functional classification: groups I (0.5), II (1.0-1.5), III (2.0-2.5), and IV (3.0-3.5). RESULTS During a typical quarter, significant increases in total distance (m), relative distance (m/min), and mean speed (m/s) were associated with an increase in classification group (P < .001), with the exception of groups III and IV. However, group IV players achieved significantly higher peak speeds (3.82 ± 0.31 m/s) than groups I (2.99 ± 0.28 m/s), II (3.44 ± 0.26 m/s), and III (3.67 ± 0.32 m/s). Groups I and II differed significantly in match intensity during very-low/low-speed zones and the number of high-intensity activities in comparison with groups III and IV (P < .001). Full-match analysis revealed that activity profiles did not differ significantly between quarters. CONCLUSIONS Notable differences in the volume of activity were displayed across the functional classification groups. However, the specific on-court requirements of defensive (I and II) and offensive (III and IV) match roles appeared to influence the intensity of match activities, and consequently training prescription should be structured accordingly.

Assessing Handheld Mobile Laser Scanners for Forest Surveys

A handheld mobile laser scanning (HMLS) approach to forest inventory surveying allows virtual reconstructions of forest stands and extraction of key structural parameters from beneath the canopy, significantly reducing survey time when compared against static laser scan and fieldwork methods. A proof of concept test application demonstrated the ability of this technique to successfully extract diameter at breast height (DBH) and stem position compared against a concurrent terrestrial laser scan (TLS) survey. When stems with DBH > 10 cm are examined, an HMLS to TLS modelling success rate of 91% was achieved with the root mean square error (RMSE) of the DBH and stem position being 1.5 cm and 2.1 cm respectively. The HMLS approach gave a survey coverage time per surveyor of 50 m2/min compared with 0.85 m2/min for the TLS instrument and 0.43 m2/min for the field study. This powerful tool has potential applications in forest surveying by providing much larger data sets at reduced operational costs to current survey methods. HMLS provides an efficient, cost effective, versatile forest surveying technique, which can be conducted as easily as walking through a plot, allowing much more detailed, spatially extensive survey data to be collected.

The validity and reliability of a novel indoor player tracking system for use within wheelchair court sports

Abstract The aim of the current study was to investigate the validity and reliability of a radio frequency-based system for accurately tracking athlete movement within wheelchair court sports. Four wheelchair-specific tests were devised to assess the system during (i) static measurements; (ii) incremental fixed speeds; (iii) peak speeds; and (iv) multidirectional movements. During each test, three sampling frequencies (4, 8 and 16 Hz) were compared to a criterion method for distance, mean and peak speeds. Absolute static error remained between 0.19 and 0.32 m across the session. Distance values (test (ii)) showed greatest relative error in 4 Hz tags (1.3%), with significantly lower errors seen in higher frequency tags (<1.0%). Relative peak speed errors of <2.0% (test (iii)) were revealed across all sampling frequencies in relation to the criterion (4.00 ± 0.09 m · sˉ1). Results showed 8 and 16 Hz sampling frequencies displayed the closest-to-criterion values, whilst intra-tag reliability never exceeded 2.0% coefficient of variation (% CV) during peak speed detection. Minimal relative distance errors (<0.2%) were also seen across sampling frequencies (test (iv)). To conclude, the indoor tracking system is deemed an acceptable tool for tracking wheelchair court match play using a tag frequency of 8 or 16 Hz.

Effects of deer on woodland structure revealed through terrestrial laser scanning

1. Terrestrial laser scanning (TLS) captures the three-dimensional structure of habitats. Compared to traditional methods of forest mensuration, it allows quantification of structure at increased resolution, and the derivation of novel metrics with which to inform ecological studies and habitat management. 2. Lowland woodlands in the UK have altered in structure over the last century due to increased abundance of deer and a decline in management. We compared whole-canopy profiles between woodlands with high (>10 deer km−2) and low deer density (c. 1 deer km−2), and in stands with and without records of management interventions in the last 20 years, providing a test case for the application of TLS in habitat assessment for conservation and management. 3. Forty closed-canopy lowland woodlands (height range 16·5–29·4 m) were surveyed using TLS in two regions of the UK, divided into areas of high- and low-deer abundance, and between plots which had been recently managed or were unmanaged. Three-dimensional reconstructions of the woodlands were created to document the density of foliage and stem material across the entire vertical span of the canopy. 4. There was a 68% lower density of understorey foliage (0·5–2 m above-ground) in high-deer woodlands, consistent in both regions. Despite this, total amounts of foliage detected across the full canopy did not differ between deer density levels. High-deer sites were 5 m taller overall and differed in the distribution of foliage across their vertical profile. Managed woodlands, in contrast, exhibited relatively minor differences from controls, including a lower quantity of stem material at heights from 2 to 5 m, but no difference in foliage density. All main effects were replicated equally in both regions despite notable differences in stand structures between them. 5. Synthesis and applications. Terrestrial laser scanning allows ecologists to move beyond two-dimensional measures of vegetation structure and quantify patterns across complex, heterogeneous, three-dimensional habitats. Our findings suggest that reduction of deer populations is likely to have a strong impact on woodland structures and aid in restoring the complex understorey habitats required by many birds, whereas management interventions as currently practiced have limited and inconsistent effects.

Contemporary surveying education changing with the times

Abstract The role of the surveyor remains relevant to the modern world, but there are notable changes in how surveyors carry out their work and in the nature of that work. This paper argues that such changes in the professional arena demand changes in the associated educational programmes. The discussions are primarily based on findings from a study of a wide cross-section of university-based surveying courses from diverse countries. Issues of curriculum and pedagogy and the relationship between education and the surveying industry are explored. As it relates to curriculum, contemporary surveying education is viewed vis-à-vis educational models. The comparison is conducted at two levels: in relation to content delivery strategies and in relation to their philosophical bases. Other issues considered to be relevant to contemporary surveying education are discussed. These include shifts in how surveying is perceived in industry and in academia, pedagogical approaches employed in surveying courses and the relevance of theories of learning to pedagogical and curricular development. This paper ends with a discussion on the nature of the relationship between university-based surveying education and the wider world of professional surveying practice.

Monitoring deformation of small scale model tunnels under load testing

Abstract This paper describes a study to assess the suitability of two non-contact methods of measurement used to monitor a series of small scale model tunnels built to different specifications that are being subjected to load testing. The model tunnels are being built to validate mathematical modelling techniques. Presented here are the results to assess the suitability and quality of survey results based on photogrammetry and laser scanning. The two key parameters to be measured are the deformation that is created in the tunnel (distance measurement) and the length and width of cracks. Results showed that both the remote measurement techniques were suitable for the measurement of the small model tunnels and compared well against appropriate potentiometer and vernier calliper measurements.

GEODETIC TRANSFORMATIONS - PART 1

Abstract Until the advent of satellite positioning and navigation systems, and in particular the Global Positioning System (GPS), geodetic coordinate systems were of little interest to many surveyors or navigators. Indeed, many of todays problems and difficulties stem from this historical misunderstanding of the true complexity of systems of coordinates. This paper will briefly describe a number of common types of coordinate representation and common coordinate systems and datums. In order to relate coordinates based on differing systems it is also necessary to understand the methods of transforming coordinates from one system to another. The methods of transforming geodetic coordinates are discussed in the second part of this paper.