plotAngStrip

Description

plotAngStrip is a specialized plotting utility designed to visualize angular response data generated by compAngStrip -ss. It reads an ASCII file containing stacked angular response curves (representing backscatter strength versus grazing angle) and plots them as a series of graphs.

The tool allows for plotting multiple stacked curves, defining custom plot ranges, and adding titles, making it suitable for analyzing how angular response varies along a survey line or between different processing stages.

Usage 

plotAngStrip -infile <file1> [-outfile <filename.meta>] [-size <dx> <dy>] [-yrange <min> <max>] [OPTIONS]

Arguments

Option Description  
-infile <file1> Required. Specifies an input ASCII file from compAngStrip -ss.  
-outfile <filename.meta> Specifies the output PostScript metafile name. plot.meta
-size <dx> <dy> Specifies the total plot size in centimeters (X and Y dimensions). 15.0 22.0
-yrange <min> <max> Sets the Y-axis range (backscatter strength in dB). -40.0 to -15.0
-together Plots all stacked curves on a single graph, overlapping.  
-sparse (Not fully implemented) Intended for sparse plotting.  
-tit1 <string> / -tit2 <string> Sets titles for the plot.  

Input File Formats (ASCII from compAngStrip -ss)

The input ASCII file is expected to contain:

  • no_stacks (int): Total number of stacked angular response curves.
  • For each stack:
    • cen_stack (int): Center stack number.
    • ByAngle[j] (double): Backscatter value for each angle bin j (0-179).

How It Works

  1. Initialization: Parses command-line arguments to set plotting options, input/output filenames, plot size, and ranges. Initializes a plotlib PostScript output (plot.meta).
  2. Plot Area Setup: Sets up the overall plot dimensions (xlength, ylength, xoff, yoff). Draws the main plot border.
  3. Title and Labels: If titles are provided, they are added to the plot.
  4. File Reading: Opens the input ASCII file from compAngStrip -ss.
  5. Stacked Curve Iteration: Reads no_stacks (total number of stacked curves) from the input file. Then, for each stack:
    • Reads cen_stack and the ByAngle[j] values (backscatter per angle bin).
    • Plotting Geometry: If together_flag is not set, it recalculates ylength and yoff to create separate vertical strips for each stack.
    • Draws a border for the current stack’s plot area.
    • Draws vertical lines at -25 and 25 degrees (related to typical grazing angle ranges).
    • Draws horizontal lines at -0 dB and the Y-axis range.
    • Curve Plotting: Iterates through j from 0 to 179 (representing angles):
      • If ByAngle[j] is valid, it converts the angle (j - 90.0) and backscatter ByAngle[j] to screen coordinates (xpos, ypos).
      • Draws a line segment from the previous valid point to the current point, creating the angular response curve.
  6. Cleanup: Calls plot_close to finalize the PostScript output and closes the input file.

Output Files

  • <outfile.meta>: A PostScript metafile (.meta) containing plots of the stacked angular response curves.

Dependencies

  • plotlib.h: For plotlib functions.
  • support.h: For general utility functions.
  • math.h: For mathematical functions.

Notes

This tool provides a visual means to track the variability of angular response along a survey line, which can be indicative of changing seafloor types or processing artifacts. The ability to plot multiple stacked curves allows for direct comparison of different segments of the data. The -sparse option is listed but not fully implemented.