To evaluate the positional accuracy of implant analogs in biobased model resin by comparing them to that of implant analogs in model resin casts and conventional analogs in dental stone casts.
...Polyvinylsiloxane impressions of a partially edentulous mandibular model with a single implant were made and poured in type IV dental stone. The same model was also digitized with an intraoral scanner and additively manufactured implant casts were fabricated in biobased model resin (FotoDent biobased model) and model resin (FotoDent model 2 beige-opaque) (n = 8). All casts and the model were digitized with a laboratory scanner, and the scan files were imported into a 3-dimensional analysis software (Geomagic Control X). The linear deviations of 2 standardized points on the scan body used during digitization were automatically calculated on x-, y-, and z-axes. Average deviations were used to define precision, and 1-way analysis of variance and Tukey HSD tests were used for statistical analyses (α = 0.05).
Biobased model resin led to higher deviations than dental stone (all axes, P ≤ 0.031) and model resin (y-axis, P = 0.015). Biobased model resin resulted in the lowest precision of implant analog position (P ≤ 0.049). The difference in the positional accuracy of implant analogs of model resin and stone casts was nonsignificant (P ≥ 0.196).
Implant analogs in biobased model resin casts mostly had lower positional accuracy, whereas those in model resin and stone casts had similar positional accuracy. Regardless of the material, analogs deviated more towards mesial, while buccal deviations in additively manufactured casts and lingual deviations in stone casts were more prominent.
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In the area of volunteered geographical information (VGI), the issue of spatial data quality is a clear challenge. The data that are contributed to VGI projects do not comply with standard ...spatial data quality assurance procedures, and the contributors operate without central coordination and strict data collection frameworks. However, similar to the area of open source software development, it is suggested that the data hold an intrinsic quality assurance measure through the analysis of the number of contributors who have worked on a given spatial unit. The assumption that as the number of contributors increases so does the quality is known as 'Linus' Law' within the open source community. This paper describes three studies that were carried out to evaluate this hypothesis for VGI using the OpenStreetMap dataset, showing that this rule indeed applies in the case of positional accuracy.
Measured trends and variability in shoreline position are used by coastal managers, scientists and engineers to understand and monitor coastal systems. This paper presents a new and generic method ...for automated shoreline detection from the largely unexplored collection of publicly available satellite imagery. The position of the obtained Satellite Derived Shoreline (SDS) is tested for accuracy for 143 images against high resolution in-situ data along a coastal stretch near the Sand Motor, a well-documented mega-scale nourishment along the Dutch coast. In this assessment, we quantify the effects of potential inaccuracy drivers such as the presence of clouds and wave-induced foam. The overall aim of this study is to verify whether the SDS is suitable to study structural coastline trends for coastal engineering practice.
In the ideal case of a cloud free satellite image without the presence of waves, with limited morphological changes between the time of image acquisition and the date of the in-situ measurement, the accuracy of the SDS is with subpixel precision (smaller than 10–30 m, depending on the satellite mission) and depends on intertidal beach slope and image pixel resolution. For the highest resolution images we find an average offset of 1 m between the SDS position and the in-situ shoreline in the considered domain. The accuracy deteriorates in the presence of clouds and/or waves on the image, satellite sensor corrections and georeferencing errors. The case study showed that especially the presence of clouds can lead to a considerable seaward offset of the SDS of multiple pixels (e.g. order 200 m). Wave-induced foam results in seaward offsets in the order of 40 m.
These effects can largely be overcome by creating composite images, which results in a continuous dataset with subpixel precision (10–30 m, depending on the satellite mission). This implies that structural trends can be detected for coastlines that have changed with at least the pixel resolution within the considered timespan.
Given the accuracy of composite images along the Sand Motor in combination with the worldwide availability of public satellite imagery covering the last decades, this technique can potentially be applied at other locations with large (structural) coastline trends.
•The positional accuracy of satellite derived shorelines can be on sub pixel level.•Several sources can deteriorate the accuracy, leading to large seaward offsets.•Inaccuracy sources are successfully mitigated, resulting in a continuous dataset.•Shoreline trends compare well to trends obtained from traditional data sources.•Satellite imagery provides a unique shoreline dataset in coastal engineering.
•The moment similarity is explained qualitatively and quantitatively.•The positional accuracy reliability at any position is calculated based on the moment similarity.•An optimal position with the ...lowest failure probability can be searched in a cubic space.
A new positional accuracy reliability analysis method of industrial robots is proposed based on the statistical moment similarity of positional error. The first-two order statistical moments of positional error at some positions are accurately obtained through the differential kinematics method to reduce the computational cost of the proposed method. In practical engineering, the statistical moments of positional error can also be obtained from the limited experimental data. Then, the statistical moment similarity of positional error is quantified by the semivariance function. Besides, the first-two order moments of positional error at any position can be calculated according to the statistical moment similarity. Thus, the positional accuracy reliability analysis of any position can be realized by the first-two order moments according to the saddlepoint approximation method. Besides, an optimal position with the lowest failure probability of positional error can be searched based on the statistical moment similarity. The effectiveness of the proposed method is manifest through calculating the positional accuracy reliability and the optimal position with the lowest failure probability of a 6-degree-of-freedom (6-DoF) industrial robot in a cubic space.
The Navigation with Indian Constellation (NavIC)/Indian Regional Navigation Satellite System (IRNSS) is an independent navigation system developed for the Indian subcontinent by the Indian Space ...Research Organisation (ISRO). The positional accuracy of this system is mainly affected by the ionosphere of the low-latitude equatorial Indian subcontinent, as large ionospheric gradients and intense irregularities are present in it. The objective of this study is to improve the positional accuracy of NavIC/IRNSS systems by applying ionospheric correction using the most suitable single-frequency model. The data to be analysed were collected from the NavIC/IRNSS receiver provided by the Space Applications Centre, ISRO. A comparative analysis between the dual-frequency model and single-frequency model (e.g. GIVE model, coefficient-based model) was performed on the data from the NavIC/IRNSS receiver. Different ionospheric models were applied to compute ionospheric delay (ionodelay) on a quiet day (3 < KP < 5). Our result shows that both the single-frequency Grid Ionosphere Vertical Error (GIVE) model and dual frequency model outperform remarkably compared to the traditional coefficient-based model. The GIVE model was also analysed on FAR categorized satellites for different stormy days of different months. It was observed that during stormy days also, the 3D position computed by applying the GIVE model was nearly the same as the dual-frequency model.
Positional accuracy is an important parameter in residual stress investigations with neutron diffraction, considering that precise measurements of strains at the same localised position along a ...number of sample orientations are required, including investigations of complete complex shaped engineering components. This study reports the development of a standardised approach for quantitative analysis of positional accuracy on neutron strain scanners that builds on previous campaigns. The approach uses standardised sample sets with specific geometries that enable quantitative assessment of instrumental and sample alignment procedures and associated accuracies. This method has been implemented on four participating instruments: ENGIN-X (United Kingdom), MPISI (South Africa), SALSA (France) and STRESS-SPEC (Germany), to render results representative of monochromatic and time-of-flight strain scanners. The benchmarking results show comparable performance between the instruments with positional accuracies around 100 μm readily achieved. This standardised approach confirms the high positional precision attainable for non-destructive stress determination, to unequivocally benefit utilisation by academia and industry alike. It is envisaged that this common calibration protocol and reporting template that conforms to the newly developed Neutron Quality Label for Internal Stress Characterisation be adopted by other facilities to facilitate expansion of the supportive network.
Robust household sampling, commonly applied for population-based investigations, requires sampling frames or household lists to minimize selection bias. We have applied Google Earth Pro satellite ...imagery to constitute structure-based sampling frames at sites in Pikine, Senegal; Pietermaritzburg, South Africa; and Wad-Medani, Sudan. Here we present our experiences in using this approach and findings from assessing its applicability by determining positional accuracy.
Printouts of satellite imagery combined with Global Positioning System receivers were used to locate and to verify the locations of sample structures (simple random selection; weighted-stratified sampling). Positional accuracy was assessed by study site and administrative subareas by calculating normalized distances (meters) between coordinates taken from the sampling frame and on the ground using receivers. A higher accuracy in conjunction with smaller distances was assumed. Kruskal-Wallis and Dunn multiple pairwise comparisons were performed to evaluate positional accuracy by setting and by individual surveyor in Pietermaritzburg.
The median normalized distances and interquartile ranges were 0.05 and 0.03-0.08 in Pikine, 0.09 and 0.05-0.19 in Pietermaritzburg, and 0.05 and 0.00-0.10 in Wad-Medani, respectively. Root mean square errors were 0.08 in Pikine, 0.42 in Pietermaritzburg, and 0.17 in Wad-Medani. Kruskal-Wallis and Dunn comparisons indicated significant differences by low- and high-density setting and interviewers who performed the presented approach with high accuracy compared to interviewers with poor accuracy.
The geospatial approach presented minimizes systematic errors and increases robustness and representativeness of a sample. However, the findings imply that this approach may not be applicable at all sites and settings; its success also depends on skills of surveyors working with aerial data. Methodological modifications are required, especially for resource-challenged sites that may be affected by constraints in data availability and area size.
Accurate kinematic modelling is pivotal in the safe and reliable execution of both contact and non-contact robotic applications. The kinematic models provided by robot manufacturers are valid only ...under ideal conditions and it is necessary to account for the manufacturing errors, particularly the joint offsets introduced during the assembling stages, which is identified as the underlying problem for position inaccuracy in more than 90% of the situations. This work was motivated by a very practical need, namely the discrepancy in terms of end-effector kinematics as computed by factory-calibrated internal controller and the nominal kinematic model as per robot datasheet. Even though the problem of robot calibration is not new, the focus is generally on the deployment of external measurement devices (for open loop calibration) or mechanical fixtures (for closed loop calibration). On the other hand, we use the factory-calibrated controller as an 'oracle' for our fast-recalibration approach. This allows extracting calibrated intrinsic parameters (e.g., link lengths) otherwise not directly available from the 'oracle', for use in ad-hoc control strategies. In this process, we minimize the kinematic mismatch between the ideal and the factory-calibrated robot models for a Kinova Gen3 ultra-lightweight robot by compensating for the joint zero position error and the possible variations in the link lengths. Experimental analysis has been presented to validate the proposed method, followed by the error comparison between the calibrated and un-calibrated models over training and test sets.
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