Aerial photography
Morteza Heidarimozaffar; Reza Zerafatyjamal; Hossein Torabzadeh Khorasani
Abstract
Extended AbstractIntroduction:The production of topographic maps by drone photogrammetry has replaced traditional mapping in many civil projects. UAV photogrammetry due to the rapid development of hardware and software can be used in many geomatic applications including agriculture, forestry, archeology ...
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Extended AbstractIntroduction:The production of topographic maps by drone photogrammetry has replaced traditional mapping in many civil projects. UAV photogrammetry due to the rapid development of hardware and software can be used in many geomatic applications including agriculture, forestry, archeology and architecture, emergency management, and traffic monitoring. Nowadays, mapping the boundaries of linear projects such as roads, water transmission canals, power transmission lines (electricity and gas), railway lines, and the like, is done by UAV photogrammetry. UAV photogrammetry has emerged as a viable alternative due to its lower cost, greater spatial and temporal resolution, and flexibility in capturing images compared to other conventional aerial and space methods. Despite various researches in this field, the effect of the imaging method on the accuracy of topographic maps has not been directly studied and tested. In this paper, the experimental conditions of UAV photogrammetric imaging methods in two modes of height-fixed and scale-fixed were considered. The effect of using accurate positioning equipment on image centers on reducing the number of required control points has also been investigated.Materials & Methods:Assessing and ensuring accuracy is very important for topographic maps. Knowledge of the number and distribution of control points throughout the project area and the optimal imaging method are effective in producing these maps. In this paper, to achieve the most optimal imaging mode and the highest accuracy in the production of topographic maps for this type of project, the effects of flight design parameters, number, and distribution of control points were studied. Also, the effect of using accurate positioning equipment of image centers on reducing the number of required control points has been investigated. Image processing without accurate information of image centers with control points, image processing with accurate information of image centers and without using control points, and image processing with accurate information of image centers and control points, were considered in two flight modes with fixed altitude and fixed scale. Of the 25 points whose exact coordinates were measured differentially by the Global Positioning System, 18 were ground control points and 7 checked points. The control of the elevation coordinates of the points was performed using the direct geometric leveling method. To evaluate the accuracy of the results, the amount of error and the accuracy of the work performed, the leveling operation was performed in a round trip between all control and checkpoints.Results & Discussion:Evaluating the accuracy of the UAV photogrammetric method in producing topographic maps related to this project, according to the criterion, the root means square of errors has been done for the control and checkpoints. In addition to calculating this criterion for control and checkpoints, the difference between the digital models prepared and the reference model was considered another criterion for comparison and evaluation. According to the results, the mean height error of all points in the constant-scale mode has the lowest value in Scenario 3. The numerical value of the mean error, in this case, was equal to 0.010 meters for control points and 0.020 meters for checkpoints. The accuracy of the models obtained from point clouds with dimensions of 0.5 meters is higher than the point clouds of 2 and 4 meters. The largest difference from the reference model is related to model 1 in the category of models obtained from 0.5-meter point clouds, which vary numerically in the range (-1.68 to 10.56) meters.Conclusion:The results of the height error evaluation of control and checkpoints show if aerial triangulation and justification of images use image center observations alone, in challenging projects the mapping of linear areas where the mapping is done in a strip area will not have the desired accuracy. The use of ground reference images alone is not sufficient and the simultaneous use of ground control points and ground reference images improves the accuracy of the results. As a result, the use of ground control points, fixed scale images, and image center information in the image processing process to produce corridor maps provides the best elevation accuracy compared to other modes. Also, the use of the initial digital elevation model of the project area in performing flight operations and capturing images with fixed scales has a significant effect on increasing the accuracy of the elevation component. Based on the comparison of the final digital elevation models compared to the reference model, the accuracy of the models obtained from the resolution of 0.5 meters is higher than 2 and 4 meters. Also, the effectiveness of filters to correct and reduce errors in digital elevation models has better results.
Morteza Heidarimozaffar; Morteza Shahavand
Abstract
Introduction Iran is mostly located in arid and semi-arid regions, and groundwater is its only water resource. The present study introduces a method based on spatial zoning evaluation which takes advantage ofFuzzy Logic and Geospatial Information System to design possible sites for an underground dam, ...
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Introduction Iran is mostly located in arid and semi-arid regions, and groundwater is its only water resource. The present study introduces a method based on spatial zoning evaluation which takes advantage ofFuzzy Logic and Geospatial Information System to design possible sites for an underground dam, and ranks them according to their suitability. The usability of this method for the construction of an underground dam in Kabodarahang Plain in the north of Hamedan Provincewas evaluated in the present study. Materials & Methods Groundwater use is considered to be a solution of water scarcity in arid and semi-arid regions. Lack of sufficient financial resources and adequate technology as well as specific physical conditions make it difficult to provide clean water in arid areas of most developing countries. Over the past few years, underground dams has been considered as a way to overcome water scarcity in arid and semi-arid regions. The present study seeks to identify suitable locations for the construction of an underground dam in Kabodarahangplain in north of Hamadan province using fuzzy logic in GIS environment. As one of the case study areas of Qareh Chai River,KabodarahangPlain isthe largest plain of Hamedan province with an area of 3448 square kilometers and an average height of about 1789 meters above the sea level.It is located between 48°14ˊ 51 ̋ to 49° 5ˊ 11 ̋ eastern longitude and 34° 50ˊ 6 ̋ to36°14ˊ 31 ̋ Northern latitude. To reach the goal of the present study, effective parameters in the constructionof underground dam, such as land slope, positionof wells, springs and aqueducts, rivers channels, positionof faults, location of villages and cities, position of paths and the thickness of alluvium were collected from the study area. Based onthe possibility of performing different spatial analyses in geographic information system environment, zoning ofKaboodarahang plain was evaluated from the point of view of an underground dam construction usingfuzzy logic and GIS tools in the present study. Results & Discussion Similar to membership in classical series,“And” operatorin Fuzzy Logic is used when two or more different criteria can help in solving an issue. This operator extracts the minimum membership level of pixel units in a specified positionand use it in the final map.Fuzzy multiplication operator multiplies membership level of pixel units in specified positionsof different factors and use the result in the final map. This operator is used when mapsof different criteria have a subtractive effect on each other.Fuzzy gamma operator is the general form of algebraic multiplication of fuzzy multiplication and addition operators to the power of gamma. It is used when increasing and decreasing effects are present in the relations between different criteria. Following the preparation of layers in Arc Map software, Euclidean distance operator and interpolation based on triangulation method were used to convert parameters to raster layers. Based on the background research and standards used, the criteria maps were combined using fuzzy operators. Using Fuzzy membership operator, an area of 3342 hectares, using fuzzy multiplier operator an area of2393 hectare (around one percent of the study area) and using the fuzzy gamma operator, an area of 35574 hectares (10.32% of the study area) was selected as having a very good potential for underground dam construction.Slope Map is also one of the most important criteria in determining areas appropriate for underground dam construction. It is suggested to use a larger-scale topographic map to improve the accuracy and increase the possibility of errors. Intelligent algorithms can also be used to determine the threshold level for standardization of the criteria. Since different organizationswork in the field of data collection, it is also suggested to providea suitable mechanism to assess the potential of other plains through consultation and coordination with other relevant organizations. It is recommended to use other parameters and factors affecting the selection of suitable areas for the construction of underground dams, such as soil type or physical and chemical properties of soil in future studies. Conclusion Zoning maps prepared by fuzzy logic in GIS environment can be used to determine the appropriate location forthe constructionof underground dams. Fuzzy operators provide special conditions which make them more reliablecompared to traditional methods.Appropriate areas for construction of underground dam were identified in GIS environment. A decision making model can also be produced based on the input parameters.It is suggested to enter general information of the area to perform the initial investigation of potential areas and then add field study information to complete the model.
