Topic:
How to create a datumed horizon.

Description:
User wants to create a horizon as a datum, subtracting the shallow horizon from
the datum horizon, then take the resultant horizon and subtract the deeper
horizon, then surface cut back as a new horizon.   

Solution:
1.) In Seis3DV, interpret around edges of survey by selecting the first and last
    inlines and crosslines and interpreting a straight line at the same time
    from first to last trace, a horizon which we'll call Datum.

2.) In MapView, go to Select > Horizon and select the Datum, Shallow and Deep 
    horizons and grid each one. 
   - After selecting the first horizon, go to Edit > Grid Contour, switch 'data
     and display mode' to 'Grid' and Exit. Repeat for each horizon.

3.) Go to Grid Operations > Combine
   - Toggle grid operation to 'Substract'
   - Toggle Input grid to 'List'
   - Type in Resultant surface name "delta_datum"
   - Exit. Select the Datum grid, then the Shallow grid.

4.) Grid delta_datum (follow gridding instructions in step 2)

5.) Go to Grid Operations > Combine 
    - Toggle grid operation to 'substract'
    - Toggle input grid to 'List'
    - Type in resultant suface name "final_datum"
    - Exit. Select the Final_datum grid, then the Deeper grid.

6.) Grid Final_datum (follow gridding instructions in step 2) 

7.) Go to Surface Cut to create new horizon.
    - Select Surface Cuts > Cut Surface Lines > Inline Range
    - Toggle '3D survey' to correct survey and Exit.
    - Select Save Surface Cuts > IESX Horizon
    - Type in 'Horizon Name', make sure 'Attribute Name' is 'TIME' and fill in
      rest of information and Exit.
    - Click on color with mb1 and Exit (lower right hand corner)

8.) Display new horizon on seismic. If horizon shows up on basemap and not
    seismic, then read in "final_datum" horizon back into Mapview, do not grid
    but select XYZ Operations > Save Points > IESX Horizon
    - Type in 'Horizon Name', make sure 'Attribute Name' is 'TIME' and fill in
      rest of information and Exit. 
    - Click on color with mb1 and Exit (lower right hand corner)




Last Modified on: 03-NOV-98