Working With Aerial Imaging to Produce Maps - Term Paper Example

Working With Aerial Imaging to Produce Maps By: Professor: Class: University: City: State: Date of submission: Working With Aerial Imaging to Produce Maps Introduction Photogrammetry is a technique used for surveying and mapping meant for various applications. Therefore, there are several uses of photogrammetry within the surveying industry including topographic mapping, planning of the site, and production of both orthophotography maps and digital elevation models (DEM). It is also vital in a vast selection of industries including manufacturing, architecture, and police investigations. Photogrammetry means measurements from photographs, which is the art that integrates both science and technology in a bid to acquire reliable information on the physical objects and environment through various processes including recording, measuring, and interpretation of images within the photographs (Hosseinzadeh, 2011, 195). There are two types of photogrammetry: terrestrial photogrammetry and aerial photogrammetry. Usually, aerial digital photogrammetry is used for topographical mapping beginning with digital photographs or videos taken from the camera, which is mounted on the airplane, which flies over the area through a meandering path to ensure that it takes overlapping photographs of the whole area to ensure complete coverage. The close range or digital photogrammetry, on the other hand, uses photographs captured within close proximity by the hand held camera or those, which are mounted to a tripod. Terrestrial photographs are important for creation of 3D models; however, they are not applicable in topographical maps. Figure 1: Workflow of Aerial Imaging ​The Saudi Arabian General Commission for Survey (GCS) The Saudi Arabian General Commission for Survey (GCS) plays a critical role in supporting the location information requirements of the Kingdom through ensuring adequate geospatial information for topography, hydrographical, and geodetic. Moreover, the institution also offers various products and services to various institutions including the government, private, and stakeholders at personal levels. The massive growth and diversification of the country’s economic performance led to urgent creation for the accurate and timely geospatial data and the hydrographical information within the varied sectors. Consequently, the state established the GCS, which embraced the responsibility to undertake geodetic, topographical survey, and production of different maps. Moreover, the institution also undertakes the responsibility of producing and disseminating various geographic information systems in a bid to boost the level of development. The recently established GCS established its objectives, which involve re-establishment, maintenance, monitoring, and controlling the national geodetic reference system s, the national tide gauge network, and the national vertical geodetic network. Moreover, the institution also conducts the national earth gravity network measurements as required within the Saudi Arabian Kingdom. In the Saudi Arabia, the GCS leads in the country in survey, charting, hydrographic and geographic information survey, and mapping. While considering the Geodetic mission of the GCS, the institution aims at developing and maintaining the accuracy and the seamless Saudi Arabia National Spatial Reference System (SANSRS) and ensure adequate accessibility to it for application within the activities involving survey and mapping of the kingdom. Since its establishment, the institution undertook various projects and some are undergoing using various photogrammetry methods including Aerial Photography Aerial Triangulation, Digital Elevation Model (DEM) Collection and Ortho-photo ensure production of maps and checking the quality of the output through integration of survey engineering concept for quality and accuracy. Digital Elevation Model In most photogrammetry departments, there have been production of numerous sheets of different scaled orthophoto maps to determine the damages of various human activities and utilize the information for development and reconstruction of new urban. The basic elements, which are vital for the production of orthophoto from the aerial photographs at various scales, are the aerial photographs taken using the most appropriate scales, ground control point with adequate density and number, and the DEM information having adequate precision and density. If the DEM information have acceptable limits of error and used majorly the production of orthophoto, then the data do not have substantial on the product accuracy; orthophoto map (Korsgaard et al., 2016). However, it is evident that the accuracy of the DEM information play critical role in the production of the contour lines within the surface of the land. Some of the small errors within the DEM information could cause errors of huge magnitude on the production of the contour lines. Besides, failure to use DEM with enough density accuracy, then the produced contour lines might not reflect properly the topographical structure of the ground surface. Two methods could be used in the fabrication of the land contour lines within the vector maps and orthophoto. Within the first method, there is automatic production of the contour lines through generation method from the DEM information produced in advance. Through the second technique, there is direct production of the contours in 3D through digitization of the stereo models designed within the stereo photogrammetric tools including analogue and digital instrument. Majorly, there are two approaches used in the of the DEM data (Le-Coz et al., 2009, 1665). Within the first approach, DEM have adequate accuracy and density that either are compatible with the photo and orthophoto scale for production collected manually or semi automatically in the analogue, analytical instrument, and compute-supported analogue. The data is collected automatically within the digital photogrammetric devices. Through the second method, the DEM data that has precise density and in regular grid form and TIN (triangular irregular network) data are removed from the digital contour lines through various photogrammetric methods. Aerial Photography Aerial Triangulation Aerial photography is the basic source of data used in making maps through photogrammetric methods. In such case, the photograph is the product of data acquisition processes. In actual sense, the net result of any photographic mission is the photographic negative. Of the major significance of measuring and interpretation are the positive reproductive from the negatives majorly known as the diaspositives (Mokarram & Hojati, 2015, 107). There are several factors that determine the quality of aerial photography including the design and the quality of the lenses used within the system, the type of camera, the photographic materials, the process of developing the photographs, and the weather condition and the angle of the sun during the photo flight. In aerial photography, image control is an important component since it is the control used in establishing the position and orientation of the camera during the exposure period. Besides, photo mosaics are no control. Nonetheless, the rectified aerial control usually requires partial control; the factors that require full control of information are mapping and orthophotography. While developing the maps using aerial photography, it is important to control the photographs using different methods. These methods include ground control points, which are surveyed normally using various survey methods; bridging the control using aerial triangulation, which is undertaken through computing the photographs common points using three successive photographs, or in the two adjacent trips and computing their 3D coordinate values (Zhang, Ding, Tang & Zhang, 2009, 137). The other method is aerial photography through kinematic GPS measurements, which would offer the position and elevation of the camera without using ground control. There are two types of ground control; photo identifiable control points and target. Target plays critical role in photogrammetric mapping that require careful consideration. Whenever the targets are positioned, it should be affected by the shadows. It is important that the targets be symmetrical in shape and of enough size (Mokarram & Hojati, 2015, 185). The ability of easily identifying the targets on a clear image assists in improving the accuracy and efficiency of the photogrammetric process. Usually, the photogrammetric control is fixed through various traditional survey methods, which needs to be spread widely. Therefore, GPS is the most effective method of surveying to establish the photogrammetric control. As a process, the aerial triangulation plays critical role in the calculation of the Y,X and Z coordinates on specified points from the measurement of photograph. Besides, areal triangulation could as well be connected to bridging. Ortho-photo Maps The conversion of any aerial photographs into map involves reassembling of different frames while removing various distortions systematically to create the plane surface or the map. Typical distortion within the aerial photography would be due to the characteristics of the camera, terrain effects, and lens distortion. Through creation an orthophoto, there are thousands of individual images of frames that could assemble and mosaiced together to ensure creation of continuous and seamless image within the targeted area. Typically, there is still breaking down of the image into various tiles while making sure it is user friendly; however, the modern compression could facilitate the imagery supply of almost the limitless extent and resolution. The orthophoto maps show various features of the through colour enhanced photographic images that have undergone through different processes to reflect the true position in details (Hassan, 2004, 92). However, these maps might or might fail to include the contours. Considering the fact that imagery tends to depict naturally the area in a more to life than any conventional line map, the orthophoto map tends to ensure provision of excellent portrayal of extensive areas around the sand, marsh, or flats areas for agriculture. Moreover, the orthophotographs are photographic images developed from either vertical or near vertical aerial photographs. Therefore, the generation process for the orthophotos tends to remove the effects of the relief terrain displacement and tilting of the aircraft. Whenever generated properly, the produced digital images have predictability associated with constant positional accuracy through the image. The digital orthophoto image is usually considered the raw within the digital aerial photo image rectified to the suitability of the DEM of similar area. It is important to note that the software used tend to merge the digital image with the DEM and ensure alignment of the image orthogonally. In the modern world, the scanning technology and the software allows various end users to generate various products that could appear as ortho-rectified image using a little cost. Nonetheless, there are techniques used in the generation of these products, which in turn produce properly positioned and accurate digital image. The application of such products is justifiable for certain projects; however, it is important to avoid confusion as the digital orthophoto. The non-digital orthophoto products in most cases are viewed as the digital image enlargements or the semi-rectified digital images. Conclusion and Recommendation Currently, there are many users of products associated with geo-spatial mapping which require various planimetric feature information. The analysis and the design of the geospatial data sets usually require features within the accurate positions. However, the collection and updating of different features associated with planimetric data could be costly. In addition, many end users are unaccustomed to viewing and analyzing the vector-based mapping data sets, which reflect their preferences on viewing the planimetric features, which they consider photo image. An orthophoto map might show the arch as unique image feature, which is identifiable easily. Since the cost of collecting and updating various planimetric features could be significant to some extent, the cost could be minimized through producing a photo-based digital map set which is considered spatially accurate throughout the image (Schenk, 2005). Besides, there are several GIS data sets, which often use of the photo based image information for various purposes. It is critical to note that the orthophoto is an aerial image that has undergone rectification. Moreover, the orthophoto usually contains feature of the line map. Through combination of the various principles of photogrammetric with the DEM data, then the process of rectification could be performed. The aerial photographs do not have constant scales throughout; however, the photography only has a point where the scale is correct which is considered mainly at the centre considering the fact that aerial photography does not undergo through rectification or the photogrammetric processes. References Hassan, M. A. (2004). Optimizing digital elevation models (DEMs) accuracy for planning and design of mobile communication networks. Sensors, Systems, and Next-Generation Satellites VII, 3(1), 87-101. Hosseinzadeh, S. R. (2011). Drainage Network Analysis, Comparis of Digital Elevation Model(DEM) from ASTER with High Resolution Satellite Image and Areal Photographs. IJESD, 4(2), 194-198. Korsgaard, N. J., Nuth, C., Khan, S. A., Kjeldsen, K. K., Bjørk, A. A., Schomacker, A., & Kjær, K. H. (2016). Digital elevation model and orthophotographs of Greenland based on aerial photographs from 1978–1987. Scientific Data, 3, 160032. Le Coz, M., Delclaux, F., Genthon, P., & Favreau, G. (2009). Assessment of Digital Elevation Model (DEM) aggregation methods for hydrological modeling: Lake Chad basin, Africa. Computers & Geosciences, 35(8), 1661-1670. Mokarram, M., & Hojati, M. (2015). Comparis of digital elevation model (DEM) and aerial photographs for drainage. Modeling Earth Systems and Environment, 1(4), 101-122. Mokarram, M., & Hojati, M. (2015). Comparis of digital elevation model (DEM) and aerial photographs for drainage. Modeling Earth Systems and Environment, 1(4), 178-199. Schenk, T. (2005). Introduction to Photogrammetry. Retrieved August 20, 2016, from http://www.mat.uc.pt/~gil/downloads/IntroPhoto.pdf Zhang, Y., Ding, H., Tang, L., & Zhang, J. (2009). Ortho updating by aerial triangulation based on existing ortho-photos and DEM. MIPPR 2009: Pattern Recognition and Computer Vision, 5(2), 133-142. Read More