An Evaluation of Recent Global Geopotential Models for Strip Area Project in Turkey

The aim of this study is to present the evaluations based on comparisons of geoid heights that are computed from several global geopotential models (GGMs) and the GNSS/levelling data. In this application framework, differences between geoid heights obtained by GGMs and GNSS/levelling were computed. Then, the availability of geoid heights calculated by GGMs for engineering applications were investigated. The Konya-Polatli (Ankara) Express Train Project as a strip area project was chosen as the study area. The length of the project is approximately 210 km and consists of 110 benchmarks that belong to the Turkish National Triangulation Network. In this study a total of 69 GGMs were compared. In order to examine more detail, these models were classified as three groups based on CHAMP, GRACE and GOCE. Each group was evaluated separately and the results were obtained. According to results, the best five models were detected for geoid height differences (NGNSS/lev-Nggm) in terms of standard deviation. These are EIGEN-6c4, EIGEN-GRACE01s, EGM2008, EIGEN-6c3stat and EIGEN-6c2, respectively. Also, geoid heights were obtained using different parametric models. These parametric models were used in order to minimize the impact of the terms of bias, tilt etc. Generally, three, four, five and seven parametric models are used for the least-squares adjustment of the geoid height differences in the literature. Therefore, in this study the geoid heights were calculated for such different parametric models. After the geoid height values were computed from the parametric models, the best global geopotential models in terms of standard deviation were obtained as EIGEN-6c2, EIGEN-6c3stat, EGM2008, EIGEN-6c4 and EIGEN-GRACE01s, respectively. Evaluación de modelos geopotenciales globales recientes para un proyecto de área lineal en Turquía ResumenEl propósito de este estudio es presentar las evaluaciones comparativas de alturas geoidales que fueron computadas a partir de varios Modelos Geopotenciales Globales (GGM, del inglés Global Geopotential Models) y la nivelación de información del Sistema Global de Navegación por Satélite. Luego se investigó la disposición para aplicaciones de ingeniería de las alturas geoidales calculadas por los modelos GGM. Se seleccionó el proyecto del Tren Expreso Konya-Polatli (Ankara) como el área de estudio por ser un terreno lineal. La longitud del proyecto es de 210 kilómetros y consiste de 110 puntos de referencia que pertenecen a la Red de Triangulación Nacional de Turquía. En este estudio se compararon 69 modelos GGM. Para un mejor examen, estos modelos se clasificaron en tres grupos basados en CHAMP (CHAllenging Minisatellite Payload), GRACE (Gravity Recovery and Climate Experiment) y GOCE (Gravity field and steady-state Ocean Circulation Explorer). Cada grupo se evaluó por separado. De acuerdo con los resultados, se detectaron los cinco modelos mejores para las diferencias de alturas geoidales (NGNSS/LEV-NGGM) en términos de desviación estándar. Estos son EIGEN-6c4, EIGENGRACE01s, EGM2008, EIGEN-6c3stat, y EIGEN-6c2. También se obtuvieron las alturas geoide a través de diferentes modelos paramétricos. Este mecanismo se utilizo para minimizar el impacto en términos de inclinación y declive. Generalmente, se utilizan tres, cuatro, cinco, y siete modelos paramétricos para el ajuste por mínimos cuadrados de las diferencias de alturas geoide, según la literatura. Por lo tanto, en este estudio se calcularon las alturas geoide con estos modelos paramétricos. Después de que se computaron los valores de altura geoide desde los modelos paramétricos, se obtuvieron los mejores modelos geopotenciales globales en términos de desviación estándar, estos son el EIGEN-6c2, EIGEN-6c3stat, EGM2008, EIGEN-6c4 y EIGEN-GRACE01s, respectivamente.

The Space Buffer Analysis Based on Grid Algorithm

Spatial analysis is the core of the space information system and the key function, and also one of evaluation a spatial information system function of the strength of the important index. Buffer analysis is the basic functions of spatial analysis on spatial information system, and is the basis of many space analysis methods. Buffer analysis is to point to identify a geographic entity or space objects on its surrounding of adjacent sex or the effect and in its built around a certain width of the strip area. In this paper, buffer area analysis of the spatial objects and grid theory are explained. On the basis of above, the establishment of grid algorithm of spatial buffer area and its shortage are also discussed. Finally, it makes exploration to the method application of the spatial buffer area analysis and the aspects of port logistics.

Analysis of Gap Patterns in Longitudinal Rumble Strips to Accommodate Bicycle Travel

Rumble strips can offer significant reductions in run-off-road crashes on rural highways. Newer ground-in rumble strip designs can be installed on a wider variety of shoulders, but these new designs have a much greater negative effect on bicycle traffic than did previous designs. The feasibility of placing gaps in a rumble strip pattern to permit bicycle traffic to cross the rumble strip area without striking the rumble strip pattern itself was investigated. A recommended minimum length for these gaps to accommodate bicyclists of varying abilities at speeds representative of downhill conditions was also determined. On the basis of experimental information collected, the researchers recommend that rumble strips on noncontrolled-access highways include periodic gaps of 3.7 m (12 ft) in length, and that these gaps be placed at periodic intervals at a recommended spacing of 12.2 m (40 ft) or 18.3 m (60 ft).