Understanding the Project_Data Grid

[tamen...@gmail.com]

Howdy,

I'm trying to understand how the Grid defined in Project_Data is actually used in the course of processing. I see that certain Geometry modules (FGD, and SPSRPS) need the Project_Data grid defined, presumably to establish the midpoint binning and populate the relevant headers, but do any other processes grab that grid for any other reasons?

I'm asking because I want to experiment with implementing a "crooked" binning for a 2D line I'm processing. Just assuming it were theoretically possible that I wrote a script to populate the midpoint-related headers (externally from cpseis) based on a meandering "grid" I put together, would it be able to play nice once brought back into cpseis? Do most modules grab midpoint info from the trace data or is it sometimes pulled from the global Project_Data info?

[cpseis-user]

Having a quick look, the grid is also used by FLEXBIN, REGBIN, DRC, PSTMIG and the DMO processes. Also the SETWORD processes can use the grid. SETWORD GRID_GLOB function will set the CDP bins (headers 7 and 8) from the XY co-ordinates. Complimentary function SURV_GLOB will recalculate XY co-ordinates to the bin centres. Otherwise most processes just use the trace headers. For a marine line, you could define simple geometry with MGD and process to brute stack without worrying about the grid.

There is a new process "GRID2D" in the latest revision of CPSeis. This will compute a grid to fit the XY coordinates of a 2D line, for example if you are reprocessing an old line and are given SEG Y file with co-ordinates and CDP number defined.

[tamen...@gmail.com]

Oh fantastic, are you the one who created "GRID2D"? Reading through the "GRID2D" notes, it seems to imply that it would support gridding for a crooked 2D line .(..."header 8 will have a range of values for crooked lines..."). I'll update to the latest revision and start playing around with this. Thank you.