extractProfile

Description

extractProfile is a command-line utility that extracts 2D depth profiles from one or more JHC-format 32-bit floating-point grid files (.r4 DTMs). The tool traces a path defined by a series of geographic waypoints, samples the DTM(s) at a regular interval along this path, and outputs the resulting profile. It also includes options for filtering (median, average) and calculating the along-track slope.

Usage 

extractProfile -wpts <waypointfile> -interval <meters> -topo <dtm1.r4> [-topo <dtm2.r4> ...] [OPTIONS]

Arguments

Option Description Default / Example
-wpts <waypointfile> Required. An ASCII file containing the waypoints that define the profile path. The default format is LABEL DEG MIN DEG MIN. -wpts my_track.txt
-interval <meters> Required. The sampling distance in meters along the profile path between waypoints. 50.0
-topo <dtm.r4> Required (can be used multiple times). Specifies a JHC float grid file to extract data from. If multiple -topo files are provided, a profile will be extracted from each one (if the path intersects it). -topo survey_area.r4
-decdeg If specified, the tool will read the <waypointfile> as simple space-separated decimal degrees (latitude longitude value) instead of the default format.  
-aplot Toggles the output format to a simple two-column file (along-track_distance value), which is suitable for direct plotting. The default output is a three-column geographic file (latitude longitude depth).  
-calc_along_slope Instead of extracting depth, this option calculates and outputs the along-track slope in degrees.  

Filtering Options

These options apply post-processing filters to the extracted profile data. A filtered output file named <waypointfile>.filt_prof will be created.

Option Description Default / Example
-filtlen <meters> Applies a running-average (boxcar) filter to the profile. <meters> specifies the full width of the filter. 500.0
-domedian <samples> Applies a median filter. The filter window size is (2 * samples) + 1. 5
-doaverage <samples> Applies a mean (average) filter. The filter window size is (2 * samples) + 1. 3

Other Options

| Option | Description | |—|—| | -use_xaxis_relative | Used with -aplot. The output’s X-axis will be the projected X-coordinate from the grid’s projection, rather than the cumulative along-track distance. | | -v | Enable verbose output. | |

How It Works

  1. Waypoint Loading: Reads the waypoint file (-wpts), parsing latitude/longitude and converting them to projected Northing/Easting coordinates.
  2. DTM Loading: Loads all specified DTMs (-topo) into memory.
  3. Path Interpolation: Interpolates between waypoints to create a series of sample points along the defined path at interval spacing.
  4. Profile Extraction: For each sample point along the path:
    • It determines the geographic coordinates.
    • For each DTM, it projects the geographic coordinates to pixel coordinates on the DTM.
    • It bilinearly interpolates the DTM to get the depth (or slope if -calc_along_slope) at that location.
    • The extracted value is stored.
  5. Filtering (-filtlen, -domedian, -doaverage): If any filtering options are specified, the extracted profile data is smoothed using the chosen filter.
  6. Output: Writes the processed profile data to either a geographic ASCII file (.profile) or a two-column plotting file (.aplot) if -aplot is specified. If filtering is applied, a filt_prof file is also generated.

Output Files

  • <waypointfile>.profile: The primary output file containing the extracted profile data (geographic or raw values).
  • <waypointfile>.aplot: Two-column ASCII file for plotting (if -aplot is used).
  • <waypointfile>.filt_prof: Filtered profile data (if a filtering option is used).

Dependencies

  • array.h: For JHC_header structure and DTM data handling.
  • support.h: For general utility functions and error handling.
  • j_proj.h: For coordinate projection functions.

Notes

This tool is invaluable for creating cross-sectional views of gridded data, which are often used for geological interpretation, engineering design, or habitat mapping. The filtering options allow for noise reduction or highlighting of specific features. The -calc_along_slope option provides insight into the terrain’s gradient along the profile.