Satellite Data Merging
The merging of the panchromatic SPOT and multi-spectral Landsat TM imagery was accomplished using a technique referred to as multi-resolution wavelet-decomposition merging. While image merging typically results in a trade off between high spatial resolution and the preservation of the spectral information, the best spectral and spatial quality are only achieved simultaneously with wavelet transform methods (Zhou et al 1998).
Aerial Photo Ortho-rectification
The photos were ortho-rectified to remove errors due to relief displacement and camera variables. The ortho-rectification procedure is summarised below:
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Contact prints were scanned at a resolution of 600 dpi (dots per inch), which approximates to a ground resolution of about 1.69 metres (8);
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Ground control points were identified from Lands (1997 1:20K);
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The camera calibration details were obtained from the camera calibration report, supplied by the Lands Department; and
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The scans were rectified using a combination of a digital elevation model (Section 4.2.1), the camera properties and the ground control points
The rectified aerial photos were colour balanced and mosaiced to form a continuous image layer.
Digital Elevation Model (DEM)
A DEM is a raster data type whose pixel or cell values represent elevation at that location. The DEM was used in the ortho-rectification of the satellite imagery (Section 4.2.1) and aerial photos (Section 4.2.1), and was generated as follows:
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Contour data form Lands (1997 1:20K) data were used. The coastline data was used as the 0 metre contour;
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The contours were converted to a Triangulated Irregular Network (TIN) data in ArcInfo (Section 4.1.5);
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The TIN was converted to a floating point lattice data structure using quintic (fifth order) inverse distance interpolation between points; and
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The lattice was then converted to a raster data structure in Binary Inter-leaved (BIL) format with a cell size of 10 metres.
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