7kTVG

Description

7kTVG is a utility designed to extract and process Time Varied Gain (TVG) data from Reson 7k (.s7k) files. It reads all 7k_7010_TVG records from an .s7k file, aggregates the TVG gain values for each ping, and then outputs them as a 2D floating-point array (JHC .r4 format). The output array represents ping number versus sample index, with each cell containing the TVG gain value.

This tool is useful for analyzing the TVG curves applied by the sonar, which is important for understanding backscatter measurements and for calibrating side-scan sonar data.

Usage 

7kTVG -in <inputfile.s7k> -out <outputfile.r4> [-v]

Arguments

Option Description
-in <inputfile.s7k> Required. Path to the input Reson 7k .s7k file.
-out <outputfile.r4> Required. Path for the output JHC .r4 file containing the TVG array.
-v Enable verbose output.

How It Works

  1. Initialization: Parses command-line arguments to get input/output filenames. Initializes Reson_7K_NF, Reson_7K_DRF, and Reson_7K_7010_TVG structures.
  2. File Opening: Opens the input .s7k file for reading and the output .r4 file for writing.
  3. First Pass (Metadata Collection):
    • Reads through the entire input .s7k file once.
    • Identifies all 7k_7010_TVG records.
    • Determines max_num_samples (the maximum number of samples found in any TVG record) and num_pings (total number of TVG records).
  4. Buffer Allocation: Allocates a 1D floating-point array outbuffer of size max_num_samples * num_pings to store all TVG gain values.
  5. Second Pass (Data Extraction and Aggregation):
    • Resets the file pointer of the input .s7k file to the beginning.
    • Reads through the input .s7k file a second time.
    • For each 7k_7010_TVG record:
      • Copies the tvg_gain array from the tvg structure into the outbuffer at the appropriate offset (this_ping * max_num_samples).
    • Increments this_ping.
  6. Output to JHC .r4 File:
    • Calls writeJHC() (an external function) to write a JHC header to the output .r4 file. The header will reflect the dimensions of the TVG array (max_num_samples as dx, num_pings as dy, and data type as JB_FLOAT).
    • Writes the aggregated outbuffer data to the .r4 file.
  7. Cleanup: Frees allocated memory and closes all files.

Output File

  • <outputfile.r4>: A JHC .r4 file (binary float array) where rows represent pings and columns represent sample indices, with each cell containing the TVG gain value.