نشریه مهندسی نقشه برداری و اطلاعات مکانی
سال دهم شماره 1 (پیاپی 37، اسفند 1397)

Considering the wide applications of accelerometers to determine position and attitude and due to reducing of accuracy of this sensors because of some errors, this paper discusses the calibration of accelerometers. Also because the traditional calibration methods are very time consuming, costly and need precision laboratory equipment, in-field calibration methods are recommended which are simple, fast, cheap and don't need equipment. In these methods, by using of gravity vector a cost function is defined and after optimization of this function, calibration coefficients includes bias and scale factor which are the most important error factors in output model of accelerometer are obtained. Then accelerometer is simulated in MATLAB software and these calibration methods are used to calibrate sensor and they are compared in terms of accuracy, pace, the effect of different noises and the effect of different initial conditions. The fastest and simplest method is least square method but all methods are the same accuracy. In term of effect of noise, four methods of Levenberg-Marquardt, Newton, quasi-Newton and least square are the same and the best and in term of effect of initial condition, the best method because of independence from value of initial-conditions is least-square and after that quasi Newton algorithm and Levenberg-Marquardt algorithm are good.

There is a growing demand for mapping and 3D modelling of buried objects such as pipelines, agricultural hetitage, landmines and other buried objects. Usually, large scale and high resolution maps from these objects are needed. Manually map generation and modeling of these objects are cost and time consuming and is dependent on lots of resources. Therefore, automating the subsurface mapping and monitoring process is becoming as an important new era of interest in remote sensing and computer vision society. One of the most interesting topics emerged in this area is the application of Ground Penetration Radars for under ground mapping and 3D modelling. As these types of sensors are new and are using in remote sensing and mapping more and more recently, in this paper we proposed to have a research on these systems and their capabilities. For the pupose, we have a short review on GPRs and their concept, capplicability and history. Then we review all the GPR based buried objects mapping and 3d modeling methods.

Volunteered Geographic Information has provided a rich and valuable resource for spatial data in a variety of applications. Despite the many benefits, this information does not provide any guarantee for their quality. So far, there are several methods to determine the quality of VGI. In addition to introducing quality elements and their evaluation methods, the present study attempts to explore existing methods for assessing the VGI quality and the quality assessment methods based on the type of information used in the evaluation process, classified into three groups of methods focused on comparing VGI data with reference data, Focuses on contributor evaluation and focused on data history. In this review study, we will try to review the methods used to assess the quality of VGI in the absence of valid and reference data.

Damages due to subsidence such as destruction of watering system and agricultural fertile soil, wells increasing, damage to the roads, bridges and high ways and disordering in the water and gas supplying usually are irreparable and costly. As a huge amount bench marks of height network of Iran are placed in the subsidence area, changing their heights is a challenge for NCC. In this study, a new application of displacement map produced by interferometric synthetic aperture radar technique in height datum determination in the subsidence area of Tehran, Qom and Isfahan provinces is introduced. Leveling observation of these areas is confirmed this application of InSAR.

Since incorrect excavations have resulted in extensive and irreparable financial and physical losses, therefore different drillings require having accurate information about the status of the infrastructures. Ubiquitous Geospatial Information System (UBGIS) as a new generation of Geospatial Information System (GIS) can be a good solution to avoid such problems.  Augmented Reality (AR) is the next generation of real-world 3D visualization that can be used to visualize this infrastructure on smart phones. These days, due to recent advances in the mobile phone hardware industry, such as increased processing power and the availability of various sensors such as GPS, accelerometer, gyroscope, compass, camera and mobile phone display, AR is easily available to developers and users. The exterior orientation parameters of camera are required for AR and tracking. These parameters can be achieved by sensors embedded in smart phones. So overview of type, performance and accuracy of sensors is critical. This paper aims to examine the performance and accuracy of the types of sensors in the smartphone in order to visualize the underground infrastructure using augmented reality technology. For this purpose, two smartphones Samsung Galaxy S4 and iPhone4 have been reviewed. The Samsung S4 also has less radial distortion than the iPhone 4 (about half) and it is possible to correct it linearly. The best accuracy of GPS is about 10-20 m. The average of compass error is about 10 degrees in flat regions and about 30 degrees in regions surrounding with high buildings. Gyroscope values drift about 3-4 degrees per second and increase gradually. Also heading values in regions surrounding with high buildings have less accuracy. Generally choosing the best sensor and smartphone depend on usage. Also Samsung Galaxy S9 and iPhone 8 as the new generation of these two operating systems are compared.

Large and astable engineering structures are the great importance and the behavior of such structures is usually made in Geotechnical and Geodetic methods (engineering geodesy). In the geodetic methods, the selection of appropriate surveying stations, in terms of distribution, locations, and distant of the target points to stations the control network, have a significant role in determining the accuracy of the coordinates. The optimal distance is obtained when the best accuracy is obtained to estimate the coordinates of the target points on the structure. In this research, modeling of optimal distances of surveying stations has been conducted for monitoring susceptible and unstable structures using geodetic methods. In order to determine the optimal distances, considering the maximum accuracy in determining the 3D coordinates, the accuracy of coordinate is analyzed and investigated based on the dependent variables. Then, the modeling was performed with a multivariate equation by evaluating the changes in the accuracy of the coordinate relation to the variations of the distance in different modes. The results of evaluation and validation of the proposed model using ground truth showed that the accuracy of the 3D coordinates is increased, as the distance of the target point to the structure of the body is less than the control stations. Also, the higher the subject's point height, the accuracy of 3D coordinates decreases. In addition, the proposed model show that the estimating the optimal distance, accuracy were calculated a maximum error 2.5 m in term of root-mean-square error (RMSE), which conventional adjustment results have a maximum error of 2.53 meters. Therefore, the average optimum distances using the proposed model were about 38 and 12 meters to determine the height and planimetric coordinates, respectively. If these optimal distances are observed, the best possible coordinate accuracy can be achieved in determining the coordinates of target points of engineering structures. Finally, obtained models in this research, can be used to determine the optimal distance between the mapping tools –such as total stations- to the construction, especially for monitoring the construction of high building or monitoring the Building facades with the best accuracy.