layout: default title: contgrid parent: Grid Tools nav_order: 12 —

contgrid

Description

contgrid is a command-line utility for generating contour lines from a JHC-format 32-bit floating-point (.r4) grid file. It creates a binary vector file (presumably in a custom format) that represents these contour lines, which can then be used for plotting or further visualization. The tool supports different map projections and allows users to specify the range of depth values to contour.

Usage 

contgrid [OPTIONS] <input_float_file.r4> <output_vector_file>

Arguments

Option Description Default / Example
<input_float_file.r4> Required. The path to the input JHC-format 32-bit floating-point grid file (DTM). bathymetry.r4
<output_vector_file> Required. The path for the output binary vector file containing the contour lines. contours.bin
-low <value> Specifies the minimum depth value (inclusive) in the input grid to be considered for contouring. (Determined automatically from data range)
-high <value> Specifies the maximum depth value (inclusive) in the input grid to be considered for contouring. (Determined automatically from data range)

How It Works

  1. File Opening: Opens the input .r4 grid file for reading and the output vector file for writing.
  2. Header Reading: Reads the JHC_header from the input file to get grid dimensions and geographic information.
  3. Contour Generation:
    • Iterates through each grid cell.
    • For each cell, it compares its value with its neighbors to identify where contour lines cross cell boundaries.
    • For each contour level within the specified low and high range, it traces the contour line by connecting these crossing points.
  4. Vector Output: Writes the generated contour lines (as a series of connected points or line segments) to the output binary vector file. The exact format of this binary file is defined internally by the tool.

Output Files

  • <output_vector_file>: A binary file containing contour lines.

Dependencies

  • array.h: For JHC_header structure and related functions.
  • support.h: For general utility functions and error handling.

Notes

The binary vector output is designed to be consumed by other internal plotting or visualization tools within the OMG ecosystem. This tool is a fundamental step in producing cartographic products from gridded bathymetry.