Coordinates Of Check Points Research Articles

Plane Accuracy of Aerophotogrammetry without Image Control Points of DJI PHANTOM 4 RTK UAV

The small unmanned aerial vehicles (UAVs) have good operability, low cost and high production efficiency in the low-altitude aerophotogrammetry. In this paper, the checkpoint coordinate data of low-altitude aerophotogrammetry from DJI PHANTOM 4 RTK UAV in the image-free controlled model are compared with the measured data of GNSS RTK. The results show that the maximum errors of the plane coordinates of checkpoints extracted by UAV were 0.067 m and 0.045 m in X-direction and Y-direction respectively and the plane mean square error (PMSE) was ± 0.051 m, which meet the rules of the national standard and industrial standard. Therefore, the low-altitude aerophotogrammetry of DJI PHANTOM 4 RTK UAV without the image control points can be effectively applied to large-scale surveying and mapping in small areas.

Testing Accuracy and Repeatability of UAV Blocks Oriented with GNSS-Supported Aerial Triangulation

UAV Photogrammetry today already enjoys a largely automated and efficient data processing pipeline. However, the goal of dispensing with Ground Control Points looks closer, as dual-frequency GNSS receivers are put on board. This paper reports on the accuracy in object space obtained by GNSS-supported orientation of four photogrammetric blocks, acquired by a senseFly eBee RTK and all flown according to the same flight plan at 80 m above ground over a test field. Differential corrections were sent to the eBee from a nearby ground station. Block orientation has been performed with three software packages: PhotoScan, Pix4D and MicMac. The influence on the checkpoint errors of the precision given to the projection centers has been studied: in most cases, values in Z are critical. Without GCP, the RTK solution consistently achieves a RMSE of about 2–3 cm on the horizontal coordinates of checkpoints. In elevation, the RMSE varies from flight to flight, from 2 to 10 cm. Using at least one GCP, with all packages and all test flights, the geocoding accuracy of GNSS-supported orientation is almost as good as that of a traditional GCP orientation in XY and only slightly worse in Z.

Scalable Checkpointing-Based Rollback Recovery Protocol for Geographically Distributed Systems

Two opposite approaches were proposed to address some scalability problem resulting from coordinated checkpointing's synchronization during failure-free operation: minimizing the number of checkpointing participants and having the checkpointing process non-blocking. However, these previous approaches, oblivious to the underlying network, may not fundamentally provide any breakthrough for ensuring high scalability required in very large-scale P2P-based systems. This paper proposes a non-blocking coordinated checkpointing protocol to significantly reduce checkpointing synchronization overhead by structuring the peer-to-peer network into a set of groups according to a particular criterion. In this protocol, among processes in a group, one is designated as representative with the following special roles, intra-group and inter-group checkpointing coordination. Intra-group checkpointing coordination addresses the checkpointing procedure among processes within a group. On the other hand, inter-group checkpointing coordination is performed only among representatives. Thanks to this beneficial feature, the proposed protocol may considerably reduce the number of checkpointing control messages routed on core networks compared with the existing ones.

Application controlled checkpointing coordination for fault-tolerant distributed computing systems

In order to provide fault tolerance for distributed systems, the checkpointing technique has widely been used and many researches have been performed to reduce the overhead of checkpointing coordination. In this paper, we present a new checkpointing coordination scheme in which the application controls the coordination activity by utilizing the communication pattern of the application program. Unlike the previous solutions which do not utilize the communication pattern of cooperating processes, it is possible to reduce the coordination effort as well as the number of checkpoints enforced to be taken. Extensive simulations have been performed to evaluate the proposed scheme and we have concluded that the proposed scheme significantly reduces the coordination overhead compared with the existing loose coordination scheme.

Quasi-synchronous checkpointing: Models, characterization, and classification

Checkpointing algorithms are classified as synchronous and asynchronous in the literature. In synchronous checkpointing, processes synchronize their checkpointing activities so that a globally consistent set of checkpoints is always maintained in the system. Synchronizing checkpointing activity involves message overhead and process execution may have to be suspended during the checkpointing coordination, resulting in performance degradation. In asynchronous checkpointing, processes take checkpoints without any coordination with others. Asynchronous checkpointing provides maximum autonomy for processes to take checkpoints; however, some of the checkpoints taken may not lie on any consistent global checkpoint, thus making the checkpointing efforts useless. Asynchronous checkpointing algorithms in the literature can reduce the number of useless checkpoints by making processes take communication induced checkpoints besides asynchronous checkpoints. We call such algorithms quasi-synchronous. In this paper, we present a theoretical framework for characterizing and classifying such algorithms. The theory not only helps to classify and characterize the quasi-synchronous checkpointing algorithms, but also helps to analyze the properties and limitations of the algorithms belonging to each class. It also provides guidelines for designing and evaluating such algorithms.

An efficient protocol for checkpointing recovery in distributed systems

The authors present an efficient synchronized checkpointing protocol that exploits the dependency relation between processes in distributed systems. In this protocol, a process takes a checkpoint when it knows that all processes on which it computationally depends took their checkpoints, hence the process need not always wait for the decision made by the checkpointing coordinator as in the conventional synchronized protocols. As a result, the checkpointing coordination time is substantially reduced and the possibility of total abort of the checkpointing coordination is reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>