Topic:
How to load a 3D survey with line and CDP numbers combined in an ensemble header word.

Description:
How to load a 3D survey with line and CDP numbers combined in an ensemble header
word.

Some processing shops will combine the Line number and CDP number into a single
header word.

For instance, a given trace with Line=1354 and CDP=3892 will only carry this
information in a single, 4 byte header word with the value 13543892      

Solution:
To get the info out of the header, follow the following steps in IESX
Datamanager> Seismic> Load Seismic.

1) Toggle loading mode to: User Defined 3D

2) Open the Define Storage dialog box and define storage as you normally would.

3) Open the Define Input Format dialog box.  Under Key parameter source, set   
   Line number, CDP number and SP number to Expression.  Next, define the
   ensemble header word as Auxiliary Value (A1), supply the Start byte and 
   set the Format to IBM(32 bit int.)

4) Click on the SP, CDP and line number expressions... box.  
   To get the line number, we will divide the header wordby 10,000, and then
   truncate the value (13543892/10000 = 1354.3892, which truncates to 1354)
   so --> LN = TRUNC(iA1/10000)

   To get the CDP number, we take the modulus of the header word and 10,000
   (mod (13543892, 10000) = 3892).
   so --> CDP = MOD(iA1, 10000)
   Note: The i is used to maintain the number above 16777216, so make sure to
         put it in there.

   Set the ShotPoint number to equal the CDP number
   so --> SP = CDP

5) Exit the Define Input Format dialog box, save your loading definition, and
   load as usual.



Last Modified on: 29-NOV-99