Author: Altan Yılmaz , Mustafa Erdoğan
Publishing Date: 2018
Volume 3 Issue 3
Terrain surface elevations are the most commonly used geographic information. These data are distributed in the form of Digital Elevation Model (DEM) and their derivatives are used for orthophoto production, 3D city models, hydrological modeling, visibility, flood, flood analysis and so on.
Although DEM can be found in many different forms, it often consists of a large number of records, each of which represents the elevation of a point in space. It is necessary to know that DEM is the result of a series of modeling and processing steps. DEM can be obtained from sources such as aerial and space radar data (artificially sparse) and laser scanning (LIDAR), with automatic correlation from aerial photos and satellite images, field measurements, contours, vector data.
The densest grid spacing DEM covering the entire country is the DTED2 data produced by the General Command of Mapping with a grid spacing of 1 second (approximately 30 m). DTED2 data was produced by using the contours, elevation points, lakes and sea areas in the existing 1: 25,000 scale topographic maps in the standards specified by NATO STANAG MIL-PDF-89020B. The root mean square error of DTED2 data is shown as ± 9 m at 90% confidence level in a test conducted in 2007.
Denser and more accurate DEM is produced by several institutions in only required areas but not covering whole country. Governmental institutions need denser, more accurate, homogeneous and countrywide DEM in order to use in orthophoto production, 3D modelling, visibility analysis and etc. This study is conducted to meet DEM demands with optimum accuracy and density by stereo aerial photos. DEM is produced in three different areas representing the general topographic structure of Turkey by using 45 cm ground sampling distance stereo aerial photos. The RMSE of the heights of three areas are respectively ± 2.51 m, ± 1.38 m and ± 1.30 m. The proposed grid spacing by INSPIRE with these accuracies is 3-30 m in flat terrain and 3-15 m in mountainous terrain.
It is concluded that 5 m grid spacing will be suitable for a countrywide DEM with these accuracies. It is also proposed that production format of DEM should be 32 Bit Floating GeoTiff.
Keywords: Digital Elevation Model, aerial photos, automatic image matching, countrywide DEM