Assessing the geometric accuracy of small-format aerial photographs based on orthophotos in urban territories

Abstract

Field data collection. In the area, using a GPS device Trimble R10 GNSS, reference points were measured. In the built-up area (option 1), 80 points were measured, and in the open area (option 2), 50 points were measured. The accuracy of the GPS receiver location was 1-1.5 cm. Remotely sensed data. The remotely sensed data were collected on 2016 09 11. Oblique aerial photographs had been taken by a NIKON D800E camera with modified lens (3 band (NIR, RED, Green) from ultra-light airplain X32 BEKAS flying altitude 1000 m above see level. Overlap of images were: side – 75%, forward – 85%. From images generated orthophoto with 0.2 m resolution. In the study, for the estimation of the geometric accuracy of the orthophoto map, points measured in the area were used. Well-seen objects are identified on an orthophoto map, and the position of those points in the area with respect to the measured points is determined as well as the mean square error of the points is calculated. The objects used for the research are the intersection of the road and the corners of the pavement.In the area of the clearly visible objects, the square error of the ortho-photographic map from the ultra-light aircraft, in relation to the photographed in the built-up area, is 1.2 meters, while the error of orthophotographic photos in the open area reaches only 0.44 meters. In open areas geometrical accuracy of orthophotos made using small format areal images is 36,6 % higher than in bult-up areas. Higher building in urban areas have influence for geometric accuracy of orthophotos. With the changing technologies, information that is easily accessible to everybody by remote methods is increasingly being used. This information is obtained using various UAV or ultra light flyers. As the amount of such information increases, it is necessary to assess the accuracy and appropriateness of this information for solving land-use problems. The main goal of the work is to evaluate the photometric properties of orthophoto made using small-format photographs in urbanized areas. The aim of the work was to raise the following tasks: to analyze and evaluate the process of orthophoto creation; to determine the geometrical accuracy of orthophoto in separate urbanized areas. Study was conducted in about 1200 ha of Kaunas city located in the middle of Lithuania. In this area are different types of urban areas, such as old town, industrial area, living area.