Flat vs Composite Mosaics

[conrad]

Greetings all,

I'm trying to wrap my brain around the differences between a flat file mosaic and creating a composite file mosaic of a rather large image. The images currently cover a 1:250k map sheet block and are in Imagine format with the IGE files. What are the advantages/disadvantages of creating the flat mosaic or the composite mosaic?

[rparker]

The advantages and disadvantages depend on the purpose of the imagery and the time you have to make the mosaic.

A flat mosaic encodes all of the tiles into one large, new image. Encoding a very large image can take time, so that is something to consider when building a flat mosaic.

A composite mosaic does not encode a new image, but copies all of the tiles into a composite file, where they can be accessed and viewed together as a mosaic. Since this method does not use an encoding process, it takes very little time even with large images. It's a bit like bundling all of the tiles together with rope or paste.

The flat mosaic, however, is faster to view, as it is one MrSID file and has optimized resolution levels (like pyramids) for fast viewing. The composite mosaic is fast when viewing the image while zoomed in, but can be slow when zoomed out if your mosaic consists of many large tiles. This is because the viewer will have to open and read many individual tiles to create the overview of the image for display.

For this reason, I recommend using the flat mosaic whenever possible.

[netultimate]

One of the main differences is a flat mosaic encodes all of the tiles into one new large image, but composite mosaics do not encode the tiles.


This may help you a lot.

Rajendran
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