Topic:
Why does the decimated volume from SeisAn have the same size as the original?

Description:
There are dead traces due to decimation during the computation process, but the
size of the vvol is the same as the original class of data.

Padded traces take up the same amount of space within a data volume.

Solution:
The seismic data is stored in 'bricks'. The size of these 'bricks' are
determined by the length of the line (number of CDP/trace per line) and the
number of samples per trace. [ line  x  CDP/trace  x  number of samples ]

Example: 
3D survey1, migrated (class) was selected as the input and the line decimation
was set to 10. The resultant output class vvol was the same size as the input.
When the decimation was set to 11, the output vvol was smaller than the input.

Explanation:
	The 'brick' for this survey is 10 lines x 2 CDP/traces. Selecting a
        decimation of 10 or less will access every 'brick' of the data and 
	write out to a similar volume.  Selecting a decimation of 11 will skip
	the first 'brick' of data and skip another 'brick' after every 100
	lines. The resultant volume is smaller by 10% or more (depending on 
	the total number of lines).  If the decimation is set to 2 CDP/traces
	there will be no reduction in file size.  Decimation set to 3 CDP/trace
	will reduce the size by 1/3 or more.

Note: These numbers will vary with surveys and will also depend on the number of
lines and CDP/trace selected to operate on.



Last Modified on: 05-MAY-99