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IKONOS Orthotransformed Images Generating using DTM from SPOT Spacecraft. / November 8, 2004 /The IKONOS spacecraft was launched from Vandenberg Air Force Base (USA) on 24 September 1999. The owner of the satellite till the beginning of 2006 was Space Imaging (USA). In February 2006 OrbImage announced merging with Space Imaging. The united company was called GeoEye. The spacecraft was placed on a low sun-synchronous 680-km orbit that enables its revisiting any region of the Earth every 2-3 days. IKONOS is designed for real-time acquiring digital images of the earth’s surface with 1m spatial resolution and multispectral data with 4m spatial resolution and 60 º nadir deviations allowing for collecting stereo images. IKONOS is a commercial earth observation satellite, and was the first to collect publicly available high-resolution imagery which is widely used for various tasks to the benefit of both public and commercial entities and even for private persons as well.
User may instead of using costly and even unpurchaseable aerial photography have the possibility of monitoring and rather frequent updating of data on vast areas of the earth’s surface. There evolve and are developed quite new lines of activity like pointed (pinpoint) farming, high-accuracy forecasting of rock and geological structure bedding, high-accuracy engineering in building of settlements, transportation and urban infrastructure, territory development planning, and ecological monitoring.
The equation with 11 parameters enables the transformation of x and y point co-ordinates in the image into ground project. Neglecting the third coordinate, this equation takes the following form:
Where x and у are the coordinates of points in the image and (X, Y, Z) are the coordinates of points on ground (ground control points).
Digital Terrain Model (DTM) comprises a set of height measurements made with a certain step (discreteness). However DTMs may differ both in accuracy, sampling increment, and simply in quality. DTMs are valuable data source when planning gas pipelines and conduits, geological and seismic analysis, designing communication and power lines and in other areas. In this instance we use the DTM constructed after the SPOT stereo pairs processing (Fig.1).
The DTM upper left corner coordinates Е: 533902.811, N: 3953680.726; the DTM bottom right corner Е: 537092.811, N: 3950670.726 in UTM projection. The number of pixels in line for a file is 319301. An array pitch (sampling) of DTM is 10m, the IKONOS image was imported with the same height and parameters in plan (10×10 pixels). In order to determine the height from the DTM file, a certain processing of source file was performed. The DTM source file is 16-bit (gray scale) and has the Raw format. The further computer-based processing required the following calculation: since the file is 16-bit, that is the height is expressed by 2 bytes then the height may calculated by the equation: H=2*256+1byte.
Space Imaging Company offers 5 levels of IKONOS data processing at a different price. The data is delivered in 8-bit or 11-bit format with ASCII metadata file.
Наиболее приемлемым по цене является продукт Geo. Он обладает самой низкой точностью и не является ортотрансформированным.
Geo Product is more fairly priced product. It has the poorest accuracy and is not orthotransformed.
Precision Product is highest-priced. It has the highest accuracy (4m). To achieve the maximum accuracy of image requires a customer to provide Space Imaging Company with ground control points for forming orthotransformed image.
Fig.2: IKONOS raw image
Approximately 35 ground control points from the 1:2000 map were used for geocoding.
Fig.3: 1:2000 Map of Teheran
Program, Results and Analysis
Fig.4: Open image and downloading of data on height from DEM file
Fig.5: List of parameters
Fig.6: Resampling by the nearest neighbor method
The image accuracy is +4 pixels along the X axis and =14 pixels along the Y axis.
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