[Users] Trace Re-sampling in OpendTect

[Arnaud Huck]

Dear OpendTect users,
You might not know it because there is no special button for it, but 
OpendTect can re-sample your (seismic and attribute) traces.

Already for computations along picksets and surfaces, re-sampling is 
necessary. Indeed, picksets and surfaces are not snapped to the nearest 
sample. As a result, when applying an attribute to those locations, the 
traces are re-sampled on the fly to get under-sampling accuracy.

Now, it is possible to store a re-sampled volume.
For over-sampling or under-sampling,  i.e. in order to modify the 
sampling rate of your volume, you have to use the "copy cube" option, 
available from the seismic manager. By using the default "Volume 
subselection", which is set to "none", the sampling rate will not be 
modified. If you press the "Select button", and mark the "Sub-volume" 
option, the new sampling rate will be defined as the one specified in 
your survey settings. By modifying the step value, you will re-sample 
your volume (if the specified step is different from the original). 
Please note that over-sampling will be done by decimation.

In general, there are many places in the software where you have this 
"Subselection" option; Import - Export - copy cube - create output. All 
of them will behave like I explained above.

In order to apply shifts that are below the sampling rate (general 
situation), please use the reference shift or delta-resample (3.0 and 
later only) attributes. Reference shift is for applying a constant shift 
to whole volume, while the new attribute delta-resample will use 
variable shifts originating from a stored volume or an attribute.

A third order polynomial interpolation is used for the re-sampling.

Best regards,
Arnaud.

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