ABSTRACT. Digital Elevation Models (DEMs) comprise valuable source of elevation data required for many engineering applications. Contour lines, slope -aspect maps are part of their many uses. Moreover, DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally-produced relief maps. This paper proposes a method of generating DEM by using Google Earth elevation data which is easier and free. The case study consisted of three different small regions in the northern beach in Egypt. The accuracy of the Google earth derived elevation data are reported using root mean square error (RMSE), mean error (ME) and maximum absolute error (MAE). All these accuracy statistics were computed using the ground coordinates of 200 reference points for each region of the case study. The reference data was collected with total station survey. The results showed that the accuracies for the prepared DEMs are suitable for some certain engineering applications but inadequate to meet the standard required for fine/small scale DEM for very precise engineering study. The obtained accuracies for terrain with small height difference can be used for preparing large area cadastral, city planning, or land classification maps.In general, Google Earth elevation data can be used only for investigation and preliminary studies with low cost. It is strongly concluded that the users of Google Earth have to test the accuracy of elevation data by comparing with reference data before using it.
DLT has gained a wide popularity in close range photogrammetry, computer vision, robotics, and biomechanics. The wide popularity of the DLT is due to the linear formulation of the relationship between image and object space coordinates. This paper aims to develop a simple mathematical model in the form of self calibration direct linear transformation for aerial photogrammetry applications. Software based on the derived mathematical model has been developed and tested using mathematical photogrammetric data. The effects of block size, number and location of control points, and random and lens distortion errors on self calibration block adjustments using the derived mathematical model and collinearity equations have been studied. It was found that the accuracy of the results of self calibration block adjustment using the derived mathematical model is, to some extent, comparable to the results with collinearity model. The developed mathematical model widens the application areas of DLT method to include aerial photogrammetry applications especially when the camera interior and exterior orientations are unknown.
A simple method for close range and aerial photogrammetry applications has been developed. The method is in the form of bundle block adjustment which utilizes only the measured distance(s) between points for generating adjusted relative three dimensional (3D) coordinate system. Software based on the proposed method has been developed and tested using simulated data. The effects of block size, number and location of measured distances, and random errors on bundle block adjustments using the proposed and the conventional methods have been studied using simulated and actual photogrammetric data. It was found that the accuracy of the bundle block adjustment using the proposed method is comparable or better than the results of conventional method. The proposed method, is suitable for photogrammetrists and non-photogrammetrists in different fields such as architectural, archaeological, forensic and aerial photogrammetry, where relative 3D coordinates system may be required. It has a significant effect on reducing the overall cost of the photogrammetric project. Merging the capabilities of the developed software and Computer Aided Design (CAD) technology, especially 3D drawing generation, widens its applications areas to include recording buildings and monuments which is necessary for architectural and archaeological applications.
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