نشریه مهندسی نقشه برداری و اطلاعات مکانی
سال سوم شماره 3 (پیاپی 11، شهریور 1391)

The conflation of spatial data is one important task concerning the generation of knowledge from available geoinformation Research in this domain has been carried out since the early 80s and is still one of the most challenging parts within the field of spatial data processing The range of tasks incorporates updating, change detection, enhancement and integration of spatial data.The current developments of Spatial Data Infrastructures (SDI) following the approach of Service-orientedArchitectures (SOA) foster the development of distributed geospatial information services. The fusion of thematically comparable resources to enhance available spatial information is one of the core goalsof SDI. This paper presents an approach towards ad-hoc conflations of distributed using spatial data, web services and OGC services.

Determination of the Earth’s gravitational field with unprecedented accuracy is now a reality, thanks to the CHAMP, GRACE and GOCE missions. In this paper, dedicated gravity field missions CHAMP, GRACE and GOCE are briefly discussed and objectives and achievements of them are reviewed. After this review, recent satellite-only gravity fields from these missions are assessed in spectral domain. It is concluded that for the lower degrees, GRACE model is superior to that of CHAMP and GOCE. In the medium frequency range, the GRACE and GOCE models show similar behavior and finally in the high frequency part of the spectrum, the accuracy of the GOCE model is higher than that of the GRACE one. At the end, geoid undulations computed from these satellite-only gravity field models are compared with that of the EGM2008 model, and based on this comparison, some important characteristics of these missions are discussed.

A second version of the ASTER GDEM (GDEM2) is released by NASA and the Ministry of Economy, Trade and Industry (METI) in mid-October, 2011. It is generated from data collected from the Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER), a space borne earth observing optical instrument. In this study, the general characteristics of GDEM2 are introduced. GDEM2 is employing an advanced algorithm to improve GDEM resolution and elevation accuracy and reprocessing a total of 1.5 million scene data including additional 250,000 scenes. A summary of the evaluations conducted by research teams on accuracies of GDEM are presented, in this study. Validation study of GDEM2 confirmed that elevation offset and horizontal resolution will be greatly improved in GDEM 2 and the enhanced horizontal resolution will serve to reduce the standard deviation of elevation and positional error.

The planning and decision making processes to reduce the effects of natural disasters are depends on the spatial data and making efficient decisions without these information is impossible. On the other hand by increasing the sources of spatial data production and different attributes of the datasets, standardization in the field of production, sharing and processing of spatial data has been taken into consideration. Nowadays GIS is the representation of GIS functionalities through the web as autonomous and interoperable services. Systems that implement OGC standards reduce the time required to find, analyze and update crucial information, as a result of open standards is that Emergency Response and Disaster Management stakeholders have more information available to them before, during and after an emergency or disaster occurs. In this paper, some of the OGC's common web service standards, that used in the modeling of fire detection use case, are presented. The used services are data access service, WFS and WCS, portrayal service, WMS, and processing service, WPS.

Many earth orbit satellites with various applications including Geomatics applications have been in orbit near the Earth. Because most of the satellites, the low-earth orbit satellites are affected by the confusion, their orbit complexity has specific challenges. Today, using dense GPS observations and accurate dynamical models, the quality of the orbit determination is also increased. In this study, errors in GPS observations will be moderated using the Kalman Filter algorithm. To prove the efficiency of the proposed algorithm, a pair of Kinematics orbit of GRACE is filtered and the results were compared with the orbit provided by the Institute GFZ.The results of these comparisons indicate that the standard deviation of orbit using the filtering with the Kalman filter is a quarter of a standard deviation Kinematics orbit.

By rapid development of Web envirement, using of Web has changed. Presenting the data and process using Web services technology is one of the most significant changes. Web services are Independet of operating system, Web browser and programming languages; also these services can present data in a standard format such as XML. One of the most important types of information is spatial data. Therefore, Web services are used for search, access, integrate, process and visualize spatial data from different data sources. Spatial Web services by supporting 3D spatial data are known as new generation of Web services. This research investigates capabilities of current 3D Spatial Web Services: Web Feature Service (WFS), Web View Service (WVS), Web Terrain Service (WTS) and Web 3D Service (W3DS). Next, these Web services are compared based on three criterias: overall architecture, presentation capabilities and level of user interaction. Finally, based on these comparisons and review, we propose several applicatons for each 3D spatial Web services.

Disaster management and emergency response, including various activities which are required to share information. A common problem in all this activities is search, access, integration and using data types that are involved in decision making and planning. One of these data sets is spatial data that is produced and updated by different organizations. Efficient sharing of this information is critical in disaster management. Therefore, it is essential that appropriate technologies such as Web services are used. Web Services enable find, access and use of spatial data to solve spatial problems with more speed and efficiency. In this study, a variety of Web services and their characteristics are introduced. Also an overview of spatial web services, and their role in disaster management is presented. At present, the OGC has developed a comprehensive collection of standards. Because of the important role of spatial information in disaster management and decision making and the need to share information from different sources, spatial web services are very important.