Closed alfbr closed 7 years ago
All output results should use same time shift as input.
The estimated background model on segy format will follow the same shift as input segy (see file for an example). Have tested to run Crava with its own background model, and it was ok.
Did we reach a conclusion here?
This should be ok. We have fixed a bug related to this issue. We have tested a case (from Flesche with
@hflesche can you confirm?
I have made a test where the input background models and the input seismic data both have start at 1900 ms (given in trace header byte 109-110, and also with
@alfbr, @hgolsen: Test results ready regarding the issue. Still open.
Ok, then I misunderstood the problem, sorry. Crava doesn't use the offset information in the traceheader of the cube (for reading or writing). When it reads the segy-cubes it uses the offset given in the modelfile. We will look into this now and try to add the information to all the written cubes. A warning to the users if the input segy offset in different from what is given in the modelfile would also be useful.
Regarding writing segy-cubes with offset in traceheader. If there are no segy-cubes (forward model / estimation mode) is it reasonable to take offset from the top of the topsurface of the interval the estimation is done in?
The ideal in that case would be that the user sets a fixed time limit for start time, but lacking that the top of the top surface is a reasonable guess. Normally you would wish to have some padding in addition, e.g. half of the wavelength.
Ok, we can add a
This is now checked in. Written segy could will now be written with offset, and using
Please clarify. Are new tags introduced, if so which? How does the optional part work, what is the default?
Sorry, I forgot the "\" before the tags, so they got lost. The new tag is the
It is as follows:
Attempted to run CravaSimplified.xml, both as it has been run earlier and with the time taken from the trace header. As I understand it, if the
Tried to run this case without
UTMx UTMy IL XL Offset Samples dt(ms) Length(ms)
495956.00 6719999.00 2000 1608 1900 376 4.00 1500.00
Using offset 1900 taken from trace header.
Crava crashed when reading the background, but I get the following logging:
UTMx UTMy CoScal IL XL Offset Samples dt(ms) Length(ms)
495956.00 6719999.00 1.0 2000 1608 0 376 4.00 1500.00
Using offset 0 taken from trace header.
Do you get the same? We can debug and see why Crava crashes. But the background I used with CravaSimplified (BG_AI_crop.sgy etc) has an offset of 0, while the segy has an offset of 1900.
I have re-checked the background AI file, and it seems to be in line with the rest. The traces have a time offset of 1900 ms, and there are no deviating traces reported in the RokDoc segy import, see attachment. SEGY time offset.pptx
You are right. This was a bug, this is fixed and checked in now. Please try again the next time you update Crava.
@alfbr there are also two new tags implemented for this issue. It is
But old tags still work (i.e., are the new tags non-intrusive, only exposing new functionality)?
Yes, that is correct.
Re-ran test today to check that segy header gets assigned the time start value. Works according to expectations! More exotic variants will not be checked, so I reckon the issue can be closed.
Fantastic, huge thanks for testing and fixing! Closing.
Time shift for SegY CRA-793