Software and Data Mosaicking Methods The mosaic method, defined as part of the mosaic dataset properties, defines how overlapping imagery is handled in the mosaic dataset. Mosaic methods define the order of the rasters that are mosaicked together to create the mosaicked image. The By Attribute mosaic method is commonly used to order imagery based on an attribute such as date. For example, Date can be set to 'Latest’ or 'Closest to May 2001.’ Alternatively, the same method can be used to set the order of imagery by other attributes (e.g., 'Highest Sun Angle’). Similar mosaic methods can be used to set the image orientation from the north, south, east, or west, which may improve the ability to see features such as the sides of houses in wide angle or oblique imagery. A default mosaic method is defined when the mosaic dataset is authored, but users can redefine the mosaicking method according to their requirements. Mosaicking methods are summarized in the accompanying table. Mosaicking method By Attribute Description Order images based on attribute defined in the table. It is used when imagery with specific properties is of most interest. Place the raster with center closest to the center of the area of interest on top. This is the default for most overlapping imagery with specific attributes. Compares the area of interest and the raster nadir point instead of the image center point. It optimizes imagery for the most vertical view. Chooses top image based on a direction specified by the client. It is useful for seeing the sides of buildings. Display only specified rasters despite any change in the area of interest. No ordering specified. The order of imagery is based on the order in the mosaic dataset table, which may change. Raster with center in the northwest corner is displayed on top. It is a simple way to fix the order of imagery. Fixes the order of the imagery based on an attribute and uses a special seamline geometry feature as the location to blend images together. It is used when it is necessary to create a static mosaic and minimize the transition from one image to the other. Mosaic Dataset Functions Mosaicking functions are operations that are applied on the fly to each raster in the mosaic dataset or to the contents of the mosaic dataset and deliver dynamically processed raster data to users. These allow multiple products to be created from a single raster source because imagery is processed as it is accessed. fx fx fx fx Hillshade Shaded relief Slope Closest to Center Aspect Mosaicking functions applied on the fly to each raster in the mosaic dataset or to the contents of the mosaic dataset deliver dynamically processed raster data and allow multiple products to be created from a single raster source. Closest to Nadir Closest to Viewpoint Lock Raster None North-West Seamline Some of the common processes applied to mosaic datasets via functions include  Stretch, Extract Bands, Normalized Difference Vegetation Index (NDVI) (to enhance imagery)  Clip, Mask (to exclude areas or classify)  Orthorectify, Pan-Sharpen (to process satellite and aerial imagery)  Slope, Aspect, Shaded Relief (when working with elevation data) Functions can be added to the individual raster datasets or the entire mosaic dataset. The functions are managed within the mosaic dataset. Note that when specific raster data products (data from a satellite sensor, for example) are added to a mosaic dataset, some functions are automatically added because these functions were defined as part of a raster type. Specifying the raster type, therefore, allows the mosaic dataset to identify and apply appropriate functions to the source raster datasets of a mosaic dataset. Here is a more detailed look at some functions that can be used when working with elevation data:  Aspect function—Identifies the downslope direction of the maximum rate of change in value from each cell to its neighbors.  Hillshade function—Generates a grayscale model of a terrain with the sun’s relative position taken into account for shading the terrain.  Shaded Relief function—Generates a shaded relief from an elevation model and color ramp.  Slope function—Calculates the rate of change of elevation for each DEM cell.  Stretch function—Enhances an image by changing properties, Continued on page 12 ArcUser Summer 2010 11 Summary of mosaicking methods www.esri.com