Extracted sub-volume with incorrect coordinates

[ivan-marroquin]

Hi,

Thanks for such great package!

I wanted to extract a sub-volume from a 3D survey. The sub-volume is defined by a range of inlines and crosslines. For that, I followed your examples. Although the sub-volume gets generated, once I export the segy file into my interpretation package. I notice that the sub-volume is miss-positioned with respect to the input 3D survey. Please refer to attached screen shot, in which I illustrate the issue. Also, you will find a copy of the script that I used to extract the sub-volume.

Many thanks for your suggestions,

Ivan

Extracted_sub_volume.zip

[ivan-marroquin]

Any comments/suggestions?

[jokva]

Hi,

My best guess is that you have a bug when you create your own CDP lookup table, rather than just copying the header as-is. I'd start by simplifying that as you don't really benefit from creating the headers from scratch.

[ivan-marroquin]

Hi @jokva

Many thanks for the suggestion. So, I decided to follow the Python code in https://github.com/equinor/segyio/blob/master/python/examples/copy-sub-cube.py

Here is my new script:
##########################################
import numpy as np
import segyio
import os

def generate_sub_volume(inline, xline, filename, outfile):
path= "E:\My_Python_Scripts\Labels_Volume\"

os.chdir(path)

with segyio.open(filename, "r") as source:
    # gather information from input segy file
    print('Inlines', np.amin(source.ilines), ' ', np.amax(source.ilines))
    print('Xlines ', np.amin(source.xlines), ' ', np.amax(source.xlines))
    print('Steps inlines/xlines', source.ilines[1] - source.ilines[0], ' ', source.xlines[1] - source.xlines[0])
    print('Start/End times', source.samples[0]/1000, source.samples[-1]/1000)
    print('Samples', len(source.samples))
    print('Sampling rate', abs(source.samples[1] - source.samples[0]))
    
    # set specifications of output sub-volume following format of input segy file
    spec= segyio.spec()

    spec.sorting= int(source.sorting)
    spec.format= int(source.format)
    
    spec.samples= source.samples
    
    step_inlines= source.ilines[1] - source.ilines[0]
    
    step_xlines= source.xlines[1] - source.xlines[0]
    
    # define indices of sub-volume of traces to extract from input volume, add 1 to acount for edge factor when slicing in Python
    range_ilines= np.arange((inline[0] - source.ilines[0])/step_inlines, (inline[1] - source.ilines[0])/step_inlines + 1, step_inlines).astype(int)
    range_xlines= np.arange((xline[0] - source.xlines[0])/step_xlines, (xline[1] - source.xlines[0])/step_xlines + 1, step_xlines).astype(int)
    
    spec.ilines= source.ilines[range_ilines]
    spec.xlines= source.xlines[range_xlines]

    # generate output sub-volume
    with segyio.create(outfile, spec) as dest:
        # copy text header
        for itext in range(1 + source.ext_headers):
            dest.text[itext]= source.text[itext]
        
        # copy binary header
        dest.bin= source.bin

        # inster modifications needed for new shape
        num_traces= (max(range_ilines) - min(range_ilines) + 1) * (max(range_xlines) - min(range_xlines) + 1)
        
        dest.bin= {segyio.BinField.Traces: num_traces}
        
        # copy headers in the new inlines
        dest.header.iline= source.header.iline
        
        # copy traces (inline mode)
        dest.iline= source.iline

if name == 'main':
# provide desired range of inlines and crosslines to generate sub-volume from input segy file
inline= [1000, 1010]
xline= [950, 960]

# provide name of input segy file
filename= 'test.segy'

# provide name of output sub-volume
outfile= 'toto.segy'

generate_sub_volume(inline, xline, filename, outfile)

##########################################

Unfortunately, the segy generated cannot be imported into my interpretation package.

What am I missing? Do you have other suggestions?

Best regards,
Ivan