Editorial

The International Federation of Surveyors (FIG) is the largest professional organisation for surveyors world-wide. The different technical and professional competencies are represented by the ten FIG commissions. They range from ‘Spatial Information Management’ to ‘Valuation and Management of the Real Estate’, to name just two of them. Usually the delegates as well as practitioners, academics and scientists meet yearly at the FIG Working Weeks and quadrennially at the FIG Congresses. Peer-reviewed and non-reviewed contributions are presented at these conferences. Some of the contributions presented at the FIG events are on topics relevant for the Journal of Applied Geodesy, especially those organised by Commission 5 ‘Positioning and Measurement’ and Commission 6 ‘Engineering surveys’. Commission 5 consists of several Working Groups such as ‘Standards, Quality Assurance and Calibration’, ‘3D Reference Frames’, ‘Vertical Reference Frames’, ‘GNSS’, ‘Multi-Sensor-Systems’ and ‘Cost Effective Positioning’. Commission 6 comprises of Working Groups such as ‘Deformation Monitoring and Analysis’, ‘Engineering surveys for design, constructive works and exploitation of buildings and transportation infrastructure’, ‘Sensor fusion, data acquisition and processing techniques for moving measuring complexes’ and ‘Wide Area Engineering Surveys for Monitoring, Features Determination and Environmental Management’. This Special Issue of the JAG presents four especially selected contributions of the FIG Working Week 2016, held in Christchurch, New Zealand, and have followed the peer-review process of this journal.

The first contribution of Zheng et al. deals with ‘Consequence of 2012 Mw8.6 Northern Sumatra earthquakes towards Sundaland plate’ and is obviously focussed on plate tectonics in conjunction with earthquakes. The authors outline the plate tectonic structure in south-east Asia especially Indonesia. They present the regional Continuous Reference Station (CORS) GNSS networks delivering coordinate time series in the ITRF2008 reference frame. The post-processing of the GNSS data was realised using the well-known Bernese software. For different CORSs pre- and post-seismic movements can be identified in addition to the four earthquakes. The overall movement magnitudes reached up to 3.4 cm per year and changed in four steps (2004, 2005, 2007 and 2012). The magnitudes as well as the azimuths of the movements changed significantly. The changes were therefore caused by these events. Finally a new velocity field and a new rotation vector for the Sundaland plate are presented.

The second paper of Pearson et al. covers a similar topic and deals with the ‘Options for developing modernized datum for Nepal following the April 15, 2015 Mw7.8 Gorkha earthquake’. The enormous change of the reference frame coordinates in Nepal caused by the well-known catastrophic earthquake event in 2015 is outlined and a semi-dynamic datum for Nepal is proposed. This proposal is based on the ITRF2014 coordinates including the movement rates. Five different velocity sets from solutions around Nepal were combined using a three parameter transformation adjustment to find reliable national movement rates. The gridded movement rates show RMS values between 1.1 and 1.3 mm/year for the two horizontal components. 1043 corrected velocity vectors were calculated in the ITRF2014 based datum. The authors also point out that the control of the datum should be carried out using an active CORS network. They even presented the planned design for the future. This means that considerable effort will be invested to finally establish the semi-dynamic datum in Nepal.

The third contribution of this special edition by Harima et al. is ‘An Investigation into the performance of real-time GPS+GLONASS Precise Point Positioning (PPP) in New Zealand’. The authors give an introduction to the challenges of real-time PPP and compare different software, such as the Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA) of the Japan Aerospace Exploration Agency (JAXA), the PPP-Wizard software of the French Centre National d’Etudes Spatiales (CNES) and the MagicGNSS software of GMV company using different dedicated real-time clock streams. The horizontal positioning accuracy varies from 4.6 cm to 9.7 cm, for the vertical component the respective values range from 8.7 cm to 12.7 cm. The PPP-Wizard software was found to deliver the best results in the New Zealand test. However, a convergence time of 30 minutes is still required for reliable solutions for a horizontal accuracy of 10 cm and a vertical one of 15 cm for all software packages.

The fourth paper is by Retscher and Höfer and titled ‘Wi-Fi location fingerprinting using intelligent checkpoint sequence’. The focus has changed from GNSS positioning to Wi-Fi positioning. The advantage of Wi-Fi is its availability indoors as well as outdoors and, especially in urban areas. The idea is to collect Wi-Fi signals from all surrounding access points using smartphones. The ‘fingerprinting’ approach compares known reference signal strengths with currently measured signal strength values. In this contribution a novel method using non-regularly-spaced reference points is analysed and further developed. These reference points are established at locations where typical signal strength patterns are to be expected, for example near building corners and may be regarded as intelligent checkpoints (iCP). The base for the calculations is the differences between reference and measured signal strengths. The research presents the out-door test results only. The investigations show that the choice of location of the reference points is important for the resulting quality. The quality of the results is estimated by rates of correct matching: being the ratio between the number of correctly assigned signal strengths to all possible matches of signal strengths. An intelligent choice of the iCPs ensures improved, and hence higher matching rates. For all examples and iCP choices these rates are above 90 %.

This special edition presents quite different scientific topics reflecting the variety of presented research from the FIG technical commissions. We hope that these examples will encourage more researchers to attend FIG Working Weeks in the future as well as convincing regular FIG Working Week attendees to support scientific journals such as the Journal of Applied Geodesy.

Editors in Chief

Heribert Kahmen

Chris Rizos

Guest Editor

Volker Schwieger