[OpendTect_Users] What is exactly ASCII Format of Seismic Data

Bert Bril bert at opendtect.org
Mon Jul 26 09:12:40 CEST 2010

Hi Ali,

> Please inform me how to define the ASCII file for in put in OpenDtect.
> What is the formated data for trace number and Posisition and what is
> for Data content.

In such situations, it may be a good idea to try to *export* a bit of
data, and see what that looks like.

The 'Simple file' format is really *simple*. The basic principle is that
every line has to contain one single trace. As always in OpendTect, the
format is completely irrelevant (tabs or spaces, number format).
Therefore I think you must have made some other mistake (like filling in
the wrong number of samples, unreasonable trace numbers, ...).

The simplest form is just a 'matrix' of data, with the trace sample
values in the rows. Like these 6-sample traces:

110.2	80	30	-0.3	-43.675	-45
102	78.3	25.4	-3	-46	-24

All the other options are 'decoration'. Thus, if your input data
contains trace number and coordinate, the file you offer to OpendTect
could look like this:

101 234567.8 3456789	110.2	80	30	-0.3	-43.675	-45
102 234569 3456803.2	102	78.3	25.4	-3	-46	-24

You can start the file with a file header, like, for example:

28      4       6

This signifies that data starts at 28 ms, the sample interval is 4 ms
(or 28 and 4m in case of depth data), and there are 6 samples per trace.

Last note: if you generate the data yourself, like in matlab, the
'Binary' option may be a good idea. For binary, the rules are:
* No whitespace at all, just binary data
* Write only local 4-byte float's and int's. Trace number,
inline/crossline and nr of samples are int's, other values are float's.
I'd always try some ascii imports/exports first, that's much easier to QC.

Cheers, Bert

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

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