Evaluation of Real-Time Kinematic Positioning and Deformation Monitoring Using Xiaomi Mi 8 Smartphone

Modern low-cost electronic devices can achieve high precision for global navigation satellite systems (GNSSs) and related applications. Recently, the pseudo-range and carrier phase have been directly obtained from a smartphone to establish a professional-level surveying device. Although promising results have been obtained by linking to an external GNSS antenna, the real-time kinematic (RTK) positioning performance requires further improvement when using the embedded smartphone antenna. We first investigate the observation quality characteristics of the Xiaomi Mi 8 smartphone. The carrier-to-noise-density ratio of L5/E5a signals is below that of L1/E1 signals, and the cycle slip and loss of lock are severe, especially for L5/E5a signals. Therefore, we use an improved stochastic model and ambiguity-resolution strategies to improve the short-baseline RTK positioning accuracy. Experimental results show that the ambiguity fixing rate can reach approximately 90% in 3 h of observations when using the embedded antenna, while the GPS/Galileo/BDS single-frequency combination is more suitable for smartphones. On the other hand, convergence takes 10–30 min, and the RTK positioning accuracy can reach 1 and 2 cm along the horizontal and vertical directions, respectively, if ambiguity is resolved correctly. Moreover, we verify the feasibility of using a mass-produced smartphone for deformation monitoring. Results from a simulated dynamic deformation experiment indicate that a smartphone can recognise deformations as small as 2 cm.

Nghiên cứu chế độ bay UAV trong khảo sát địa hình công trình dạng tuyến - ứng dụng cho đoạn đường đê Xuân Quan, Hà Nội

Giải pháp thành lập bản đồ địa hình bằng thiết bị bay không người lái (Unmanned Aerial Vehicle - UAV) đang ngày càng phổ biến ở Việt Nam. Đã có nhiều nghiên cứu chứng minh thiết bị UAV đảm bảo độ chính xác thành lập bản đồ địa hình tỷ lệ lớn, tuy nhiên chưa có các giải pháp cụ thể cho công trình đặc thù dạng tuyến. Mục tiêu nghiên cứu của bài báo là các chế độ bay phù hợp cho công tác khảo sát địa hình các công trình dạng tuyến. Đối tượng thực nghiệm, một đoạn đường bộ thuộc địa phận đê Xuân Quan, Hà Nội, được khảo sát bằng thiết bị UAV Phantom 4 Pro với các chế độ khác nhau trên các phần mềm điều khiển bay có sẵn. Kết quả thực nghiệm các chế độ bay được so sánh với kết quả đo định vị động thời gian thực (Global Navigation Satellite System/Real Time Kinematic - GNSS/RTK) để đánh giá độ chính xác. Nghiên cứu chỉ ra kiểu bay dải phủ trùm, đối với công trình dạng tuyến, thích hợp ở các giai đoạn thiết kế kỹ thuật và thiết kế thi công. Trong khi kiểu bay 2 dải đơn phù hợp và hiệu quả cho các quá trình quy hoạch, đánh giá sơ bộ công trình dạng tuyến.

Accuracy Assessment of the Network Real-Time Kinematic Techniques for Geodetic and Plane Coordinates

Virtual Reference Station (VRS), Master-Auxiliary Corrections (MAX) and Individualised Master-Auxiliary Corrections (IMAX) are among the Network Real-Time Kinematic (NRTK) techniques supported by Malaysia Real-Time Kinematic GNSS Network (MyRTKnet) in rendering network-based solution to users. However, different network corrections have different limitations due to different manufacturers hence offering varieties output. Therefore, this study was conducted to assess the accuracy of VRS, MAX and IMAX for geodetic and plane coordinates. Three (3) techniques were implemented to observe points at Universiti Teknologi Malaysia (UTM) and cadastral lot in Johor Bahru. The results were analysed based on assessment with known values and baseline lengths. The findings showed that the accuracy of all techniques ranged from 0.16 to 3.61 cm (horizontal) and 2.86 to 6.20 cm (vertical) for geodetic coordinates. For plane coordinates, the values varied from 0.3 to 4.22 cm (horizontal) and 2.1 to 8.26 cm (vertical). IMAX provided the worst accuracy compared to others due to incompatibility of Radio Technical Commission for Maritime Services (RTCM) format. Moreover, the accuracy decreases as the baseline length between rover and reference station increases. In conclusion, VRS and MAX yielded acceptable accuracy and can be safely chosen rather than IMAX. Furthermore, the baseline length for applications involving high accuracy measurement should also be considered.

The Integration of GPS/BDS Real-Time Kinematic Positioning and Visual–Inertial Odometry Based on Smartphones

The real-time kinematic positioning technique (RTK) and visual–inertial odometry (VIO) are both promising positioning technologies. However, RTK degrades in GNSS-hostile areas, where global navigation satellite system (GNSS) signals are reflected and blocked, while VIO is affected by long-term drift. The integration of RTK and VIO can improve the accuracy and robustness of positioning. In recent years, smartphones equipped with multiple sensors have become commodities and can provide measurements for integrating RTK and VIO. This paper verifies the feasibility of integrating RTK and VIO using smartphones, and we propose an improved algorithm to integrate RTK and VIO with better performance. We began by developing an Android smartphone application for data collection and then wrote a Python program to convert the data to a robot operating system (ROS) bag. Next, we established two ROS nodes to calculate the RTK results and accomplish the integration. Finally, we conducted experiments in urban areas to assess the integration of RTK and VIO based on smartphones. The results demonstrate that the integration improves the accuracy and robustness of positioning and that our improved algorithm reduces altitude deviation. Our work can aid navigation and positioning research, which is the reason why we open source the majority of the codes at our GitHub.

Avaliação da qualidade posicional de dados espaciais gerados por VANT para aplicações cadastrais do cemitério municipal de Monte Carmelo, Minas Gerais

Mediante a avaliação da qualidade de produtos cartográficos, surgiram-se especificações e técnicas com finalidade de regulamentar e padronizar processos relacionados à produção cartográfica nacional, em particular, a digital. Neste trabalho, destaca-se a importância da utilização de técnicas estatísticas no controle da qualidade posicional em dados espaciais. Para isso, avaliou-se uma imagem adquirida por VANT (Veículo Aéreo Não Tripulado), usando as feições pontuais (pontos homólogos utilizados para verificação dos dados a partir de informações confiáveis), conforme o padrão de acurácia posicional brasileiro (Decreto-lei 89.817 aliado à ET-ADGV) e utilizando como referência, dados obtidos por meio de um levantamento geodesico executado através do método de posicionamento RTK (Real Time Kinematic). Duas situações foram consideradas na avaliação da qualidade posicional: a primeira referente à utilização da imagem não corrigida geometricamente (mantendo apenas informação posicional do VANT) e a segunda relativa ao uso da imagem corrigida geometricamente. Dos resultados obtidos, observou-se que, a partir das coordenadas homólogas coletadas através da imagem corrigida, as amostras não apresentaram tendência, revelando-se serem livres de erros sistemáticos, sendo classificada na classe A. No entanto, ao utilizar dados da imagem sem correção, obteve-se uma classificação C de acordo com o PEC (Padrão de Exatidão Cartográfico).

A novel partial ambiguity method for multi-GNSS real-time kinematic positioning

Recent progress in using real-time kinematic (RTK) positioning has motivated the exploration of its application due to its high accuracy and efficiency. However, poorly-observed satellite data will cause unfixed ambiguities and markedly biased solutions. A novel partial ambiguity resolution method, named the irrespective of integer ambiguity resolution (IIAR) model, is proposed and applied to improve the reliability of ambiguity resolution. The proposed method contains initial ambiguity resolution and irrespective of integer ambiguity processes. The initial ambiguity resolution process applies an iterative partial ambiguity resolution method to obtain an approximate solution. The irrespective of integer ambiguity process transforms the approximate solution to a high-precision solution. Experiments show that the approximate solution is unreliable when the initial ambiguity resolution process has small redundancy, and the proposed method can obtain better results for those cases. The IIAR method showed about a 40% improvement of multi-GNSS ambiguity success rate and about a 25% improvement of standard deviation. Therefore, these results show that the proposed IIAR method can improve the results of multi-GNSS RTK positioning significantly.

ANÁLISIS COMPARATIVO DE SOFTWARE PARA OBTENER MDT CON FOTOGRAMETRÍA RPAS

Los RPAS (Sistemas de aeronaves pilotados a distancia) son muy utilizados en fotogrametría para la toma de imágenespor su alta resolución espacial y rapidez de respuesta, pudiendo llegar a zonas de difícil acceso, siendo importante diseñarun buen procedimiento en campo para minimizar los errores en la toma de datos. Se recomienda utilizar puntos de apoyo(PA) terrestres utilizando RPAS convencional, que no trabajan con sistemas RTK (Real Time Kinematic). Asimismo,existen en el mercado programas fotogramétricos libres y licenciados para generar modelos digitales de superficie (MDS),del terreno (MDT) y ortofotomosáicos. En este artículo se utilizan dos programas fotogramétricos para procesar imágenescapturadas con RPAS como son Agisoft Metashape y Recap Photo, utilizando puntos de apoyo y control terrestre. Elestudio se llevó a cabo en Almenara (España) donde se hizo el levantamiento topográfico con RPAS, capturándose 100imágenes digitales, en un área de 0.38 km2. Se utilizaron 6 PA con la finalidad de orientar bien las imágenes digitales enel sistema de coordenadas local y realizar de forma adecuada la georreferenciación de las imágenes obtenidas duranteel vuelo. Para la obtención del MDT se utilizó el software CloudCompare para hacer el filtrado en la nube de puntosobtenidas de ambos softwares. Los resultados muestran una diferencia en altura entre los dos MDT menor a 28 cmtomando como referencia el MDT de la nube de puntos de Agisoft metashape y en cuanto al error en los puntos apoyoRecap Photo presento mayor error.