Photographic Image Properties and Their Correlation With the Quality Requirements for Aerial Mapping

Introduction

Recently, cartographic products obtained by the use of photogrammetric methods are increasingly applied in digital public spaces. Many photographic images stored and employed in GIS are orthophotos. Orthophotography is a geometrically corrected (rectified), undistorted photographic image of an area with a constant scale over the entire area. The digital orthophoto map is linked to the geographic and reference coordinate system, so the positions of each image element (pixel) of the photographic image can be determined (Förstner & Wrobel, 2016; Konecny, 2003; Kraus, 1997; Kraus, 2000; Linder, 2009; Wolf et al., 2014).

The technology of UAV-Photogrammetry is becoming more and more popular using to obtain photographic images, when the area or other object is photographed with a digital camera integrated in an Unmanned Aerial Vehicle (UAV) flying at a low altitude, and the photographic images are processed with special software. A light flying machine with a computerized aerial photography system and automated flight control is an effective tool for collecting photogrammetric data. The aerial mapping system consists of an Unmanned Aerial Vehicle (also called a Drone) with flight control equipment, various types of cameras, a global positioning system (GPNS), a laser scanner and a software package for processing photographic images (Armenakis & Patias, 2019; Černiauskas & Bručas, 2014; Ghilani & Wolf, 2012; Kraus, 2007; Ruzgienė, Aksamitauskas, Daugėla et al, 2015; Ruzgienė & Aleknienė, 2004; Xiang et al., 2019).

UAV-Photogrammetry technology is applied for mapping of various objects: surfaces covered by leaf of trees, narrow linear objects (road network, sea coast, etc.), high-rise buildings, cultural heritage, cadastral areas, fixing power grid lines, etc. The technology of aerial photography from a low height and the processing of the obtained photographic images is increasingly changing the traditional methods of geodetic and photogrammetric measurements used for mapping. By the use of UAV-Photogrammetry technology photogrammetric data are obtained in real time, cartographic products meets the required accuracy and can be created quickly, is possible easy to get aerial photographs of inaccessible and complicated terrain, and the cost of aerial cartographic works is not high and are decreasing (Eisenbeiss, 2009; Haala et al., 2011; Neitzel & Klonowski, 2011; Ruzgienė et al., 2020; Systems–Unmanned Aerial Photography, n.d.).

Using UAV-Photogrammetry technology, spatial surface models are created and digital orthophoto maps are generated. The resulting products can be presented to users in an interactive way. The elevation models (DEM) and surface models (DSM) can be delivered in various forms of visualization. The innovative software system Pix4Dmapper is increasingly used to process photographic images, which combines the technologies of computer vision, geoinformation systems and traditional photogrammetry and effectively facilitates the user's work. This software is a digital photogrammetric workstation that generates aerial cartographic products and models the surface of objects. The software system can process thousands of photographic images obtained from close-range photography, drones and aircraft. Accurate georeferenced 2D/3D surface models and point clouds are created (Pix4D Support, n.d.; Rock et al., 2011; Ruzgienė, Berteška, Gečytė et al, 2015; Watts et al., 2012).