[OpendTect_Users] SEG-Y: Coordinates for 2D lines

[Bert Bril]

Hi,


I often get the question whether coordinates for 2D lines can be loaded 
from a separate 'navigation file'.


As you may know, OpendTect requires two pieces of information from the 
trace headers:

1) There must be a valid, well-behaved trace number (usually a CDP 
number). Well-haved means: no duplicates, no reversals. In 4.3 you can 
quickly check this by inspecting the plot in the examine window. The 
trace number simply has to be in the headers, as opposed to the optional 
'Ref/SP' number (which will only show up in various places, and will be 
written to SEG-Y exports).

2) Coordinate information must be available. Usually the coordinate 
information is in the trace headers. If nothing usable is available in 
the trace headers, then you can load coordinates from an external file.

The problem with 'navigation files' is that they come in a very wide 
range of formats, and some popular ones are not even 'table' files. For 
this reason, you have to produce simple files with 3 columns: 
TraceNumber, X and Y; for example:

101 345678.5 4567890
102 345655 4567899.2
107 345522.1 4568100.7

Only a file with that exact structure can be used. To use such a file, 
un-check the 'X-coordinate' in the trace header definition window, and 
two options will appear: 'Nr X Y file' and 'Generate'. With the latter 
you can define 100% straight lines.


As you can see in the example, not all trace positions need to be in the 
file, only bend points are required (OpendTect will inter- and extrapolate).



- Bert

-- 
-- Bert Bril / OpendTect developer at dGB
-- mailto:Bert.Bril at opendtect.org , http://opendtect.org