MOSAIC SATELLITE IMAGES OR MERGE SATELLITE IMAGES

In this brief instruction we will help you on the way on how to merge satellite images and raster maps into a mosaic. The tool in ILWIS to do so is called " Glue Maps ".

After you prepared your images or raster files into ILWIS format, you can now create a mosaic of several contiguous areas. 

The Glue raster maps operation glues or merges two or more georeferenced input raster maps into one output raster map mosaic. The output map then comprises the a mosaic of the total area of all input maps. The domains of the input maps are merged when needed. With the "Glue raster maps operation", you can thus merge two or more adjacent or partly overlapping raster maps (i.e. make a satellite image mosaic) or glue smaller raster maps onto a larger one.

When the input raster maps have attribute tables, also the tables will be automatically merged; for more information see the Glue tables operation.

Input maps: In the dialog box, you can select 2, 3, or 4 input raster maps. On the command line, you can specify as many input maps as you like. The input maps may be purely adjacent to one another, partly overlapping, or totally overlapping. When the input maps are (partly) overlapping, the input maps form a pile of maps on top of each other.

Map on top: When the pile of input maps are (partly) overlapping the same area, you have to decide which map should be considered as the map on top. When for a pixel a value is found in the map on top, that value will appear in the output map or satellite image mosaic. When the undefined value is found in the map on top, the operation will look in the map 'below' it. Undefined pixels thus act as being transparent and provide 'openings' to enable the operation to find a value in the map below the current one.

In the dialog box, you can select the check box 'Last Map on Top' to order the input maps as:

On the command line, you can use the Replace option to this end.

Then, for each pixel, the operation will do:

Only when no value is found at all, the output pixel will be assigned the undefined value. Mind: when the output map uses the Image domain, this means value 0; when the output map uses a Picture domain or the Color domain, this means color (0,0,0), i.e. black.

Output georeference / First input map:

If you wish, you can specify to use an existing georeference for the output map (both dialog box and command line), or you can create a new georeference corners yourself for the output map or satellite image mosaic (dialog box only). Tip: When you choose an existing georeference corners or create a new georeference corners, then the output map will always be North-oriented.

When no existing georeference is specified, and when you did not create a georeference yourself, the system will, if required, automatically construct a georeference for the output map; it will be sized in such a way that all input raster maps will fit in the new georeference.

For more information on merging satellite images into mosaics of satellite images, consult the manuel.