splitOMG

Description

splitOMG is a utility designed to extract a subset of profiles (pings) from an OMG-HDCS merged file into a new merged file. It can split files based on either a numerical range of profiles or a time-based range.

Additionally, it has a specialized mode (-into_natural_lines) to analyze the vessel’s speed and change in heading between pings, which can be used to identify natural line breaks in survey data.

Usage 

splitOMG <OMG_HDCS_infile> <OMG_HDCS_outfile> [OPTIONS]

Arguments

Option Description
<OMG_HDCS_infile> Required. The path to the input OMG-HDCS merged file.
<OMG_HDCS_outfile> Required. The path for the new output OMG-HDCS merged file containing the subset of data.

Splitting Options (Choose one or more)

| Option | Description | |—|—| | -first <ping_num> | Specifies the starting ping number (inclusive) for the subset. | | -last <ping_num> | Specifies the ending ping number (inclusive) for the subset. | | -time_start <year> <jday> <hr> <min> <sec> | Specifies a date and time range for the subset. The tool will find the corresponding ping numbers. | | -time_end <year> <jday> <hr> <min> <sec> | Specifies a date and time range for the subset. The tool will find the corresponding ping numbers. |

Analysis Option

| Option | Description | |—|—| | -into_natural_lines | Instead of splitting, this mode calculates and outputs the vessel’s speed (in knots) and change in heading (in degrees) between consecutive pings. The output is an ASCII file (<OMG_HDCS_outfile>) with ping number, speed, and dhead. This option overrides the splitting functionality. | | -minknots | (Present in USAGE but not implemented) Likely intended to filter based on minimum speed. | | -minturn | (Present in USAGE but not implemented) Likely intended to filter based on minimum turn. |

Other Options

| Option | Description | |—|—| | -v | Enable verbose output. | |

How It Works

  1. Input Reading: Opens the input merged file and reads its summary header.
  2. into_natural_lines Mode:
    • If -into_natural_lines is specified, the tool allocates memory for speed_knots and dhead arrays.
    • It iterates through each ping (from 1 to numProfiles - 1):
      • It reads the current and previous profile headers.
      • It locates the transducer position for both pings.
      • Calculates the geographic distance and time difference between the two ping positions.
      • Computes the vessel’s speed in knots (speed_knots) and the change in heading (dhead) between the pings.
    • It then writes these calculated speed and heading change values (ping number, speed_knots, dhead) to the specified OMG_HDCS_outfile as an ASCII listing.
  3. Splitting Mode (Default):
    • If into_natural_lines is not specified, the tool determines the first and last ping numbers for the subset. This can be directly from -first/-last options or by performing a time-based search using OMG_HDCS_time_search if -time_start/-time_end are provided.
    • It performs error checks to ensure the first and last ping numbers are valid.
    • A new output merged file (OMG_HDCS_outfile) is created.
    • The summary header from the input file is modified to reflect the new numProfiles (i.e., last - first) and then written to the output file.
    • It then iterates from first to last - 1 in the input file:
      • Reads the profile header and raw beams for the current ping.
      • Writes these profile and beam data to the new output merged file.
  4. Cleanup: Closes all open files.

Output Files

  • <OMG_HDCS_outfile>: A new OMG-HDCS merged file containing the subset of data (if splitting) or an ASCII file with speed and heading change (if -into_natural_lines is used).

Dependencies

  • OMG_HDCS_jversion.h: For OMG-HDCS data structures.
  • support.h: For general utility functions and error handling.
  • j_proj.h: For coordinate projection functions.

Notes

splitOMG is a versatile tool for managing merged data, allowing for either precise extraction of subsets for further processing or for analysis of survey line characteristics. The -into_natural_lines mode is particularly useful for quality control, helping to identify turns or changes in vessel speed. The tool always creates a new output file, preserving the integrity of the original. The -minknots and -minturn options are listed in the usage but not implemented.