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GCFXtract Shot-files

GCFXtract is a multi-platform tool for reading disks which were written in the DFD format, as used by Güralp digitisers, including 6TD digital instruments. GCFXtract can convert GCF input data into (non-Passcal) SEG-y format. Because this format limits the number of samples that can be recorded into a single file, a "shot-file" is used to specify a starting time for each individual output file. This document explains how to prepare and use shot-files.

The shot-file consists of lines, each of which specifies a single "shot time" which corresponds to a single output file. Each such line consists of three fields, separated by commas:

Lines which are not in this format are silently ignored so comments, column headers and other information can be freely incorporated.

An example shot-file might look like this:

Sample shot-file for GCFXtract Shot Number,Human Time,Unix Time 7,09/08/2014 09:17,1407575844.129800 6,09/08/2014 09:17,1407575852.697800 5,09/08/2014 09:17,1407575861.061800 4,09/08/2014 09:17,1407575869.347800 3,09/08/2014 09:17,1407575877.913800 2,09/08/2014 09:18,1407575886.355810 1,09/08/2014 09:18,1407575894.751810

The shot-file can be specified using the GUI interface or from the command line. If specified on the command line, the pre-shot data duration and the post-shot data duration must also be specified. The following arguments are relevant to SEG-y files:

A typical invocation might look like this:

gcfxtract /d:segys /s:C:\Data\ShotFile.csv /div:1 /post:7 /offs

This would direct GCFXtract to record files with eight-second durations - one second pre-shot and seven seconds post-shot - using shot times from C:\Data\ShotFile.csv and with DC-offset-removal active.

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