Ömer Gökdaş

OpenStreetMap (OSM), ulaşım ağı modellemesi, coğrafi bilgi sistemleri ve mekânsal ağ analizleri için yaygın biçimde başvurulan bir açık veri kaynağıdır. Ancak OSM yol ağı verisi mekânsal olarak homojen değildir; yoğunluk, topolojik tutarlılık ve öznitelik doluluğu iller arasında belirgin biçimde farklılaşabilmektedir. Bu makalede, Türkiye’nin 81 ilindeki OSM driving yol ağı içsel kalite göstergeleriyle değerlendirilmiştir. Amaç, iller arası karşılaştırmalı bir kalite profili sunmaktır. Bunun için Geofabrik’ten elde edilen Türkiye OSM PBF verisi ile GADM düzey-1 il sınırları birlikte kullanılmış; driving yol ağı çıkarılmış, yol segmentleri orta nokta temelli atama yöntemiyle illere bağlanmış, yoğunluk, topoloji ve öznitelik tamlığı boyutlarında göstergeler hesaplanmış, ardından eşit ağırlıklı ve topoloji ağırlıklı olmak üzere iki bileşik skor üretilmiştir. Sonuçlar, iller arasında belirgin kalite farklılıkları bulunduğunu göstermektedir. Büyükşehirlerde daha yoğun ve bağlantılı ağ yapıları gözlenirken bazı illerde öznitelik tamlığı ve bileşik skor görece düşük kalmaktadır. Çalışma tekrarlanabilir bir Python iş akışı, il bazında karşılaştırmalı kalite profilleri ve OSM verisi kullanan araştırmacılarla uygulayıcılar için pratik bir gösterge seti sunmaktadır.

The geometric design of the Continuously Operating Reference Station (CORS) network is one of the most critical factors that impact accuracy, precision, and Time to Fix Ambiguity (TTFA) performance. In this study, the authors investigate the subject of geometric design by using both local ISKI CORS and national CORS-Turkey (CORS-TR) networks, and they redesign the ISKI CORS network by increasing interstation distances. For three systems, real-time Virtual Reference Station (VRS) solutions have been obtained and tested with Analysis of Variance (ANOVA). As a result, the 8-station ISKI CORS provides the most accurate results in the vertical component. In contrast, for TTFA performance, the CORS-TR network shows worse outcomes than the others. Due to the increase in the interstation distances, the increase in the base length caused worse results in FIX solution ratios for redesigned ISKI CORS. In summary, the authors have stated that the 8-station ISKI CORS network performs better, especially regarding vertical accuracy. Furthermore, the authors state that the TTFA performance and FIX solution ratios are high, and the ISKI CORS geometric design is optimal.

Before now, the various studies that have been undertaken to investigate the positioning performance of GNSS Online Services have been limited with regard to both time and number of sessions. Within the scope of this study, the accuracy of the velocity models estimated by APPS and AUSPOS are analysed using a wider period. Local ISKI CORS Network stations are used as the subject. To generate true values for an accurate comparison, 129 sessions with BERNESE (v5.2) software were conducted between 2008 and 2019. A linear trend was determined by using least-squares adjustment to obtain true velocity values. To test the reliability of the true velocity values, seasonal, semi-annual and annual oscillation movements have been examined. Additionally, the coherence of the velocity model with the sample data and compliance with the tectonic plate has been investigated. For GNSS Online Services, 34 sessions were carried out over the same timescale, and the velocity model was estimated. A Z-test with a 0.05 significance level was used to examine the performance of APPS and AUSPOS velocity values. As a result, the estimated true velocity model shows high compliance with sample data and the tectonic plate; no seasonal, semi-annual or annual oscillation movements were identified. According to the study’s statistical test, the velocity model of APPS solutions performs slightly better than that of AUSPOS. However, both services show high performance in the velocity determination. In summary, the usability of GNSS Online Services in determining velocity has been shown with this study.

This study examines the effect of baseline length on accuracy and precision in Network Real-Time Kinematic (NRTK) positioning and develops an experimental mathematical model to express this effect. The study also measures the performances of the Flaechen Korrektur Parameter (FKP) and Virtual Reference Stations (VRS) methods at different baseline lengths. The study makes use of the stations that form two Continuously Operating Reference Station (CORS) networks, one of which is local and the other national. Calculations were made to perform various geodetic operations, such as datum transformations between the two networks, identifications of positional velocities, and epoch shifting. BERNESE (v5.2) software was used to identify coordinate values assumed to be true based on International GNSS Service (IGS) products. No significant changes were observed in the RMSE values in baseline lengths of up to 40 km. In contrast, an average linear correlation of 69.2% was determined between precision and baseline length. Measurements were evaluated and tested using the variance model created as a function of the baseline length, in line with the aims of the study, and the results were found to be consistent. Moreover, in an examination of the Root Mean Square Error (RMSE) and precision values of the FKP and VRS measurements, no significant differences were observed. The mean differences were at the millimetre level.