layout: default title: edhead parent: Grid Tools nav_order: 23 —

edhead

Description

edhead is a powerful and versatile utility for viewing, interactively editing, and exporting metadata from the headers of JHC-format grid files. It serves as a bridge between the OMG-HDCS grid formats and external GIS applications by generating standard georeferencing files (e.g., for GeoTIFF, ESRI, KML). It can also be used to manually inspect or correct corrupted or inaccurate header information.

Usage

edhead can be run in several modes:

  1. Show Header Info: 
    edhead -show <grid_file>
  2. Export Georeferencing Data: 
    edhead <export_option> <grid_file>
  3. Interactive Edit: 
    edhead <grid_file>

Arguments

Display and Export Options

These options run non-interactively to display information or generate metadata files.

Option Description
-show Displays the full JHC header in a human-readable format and exits.
-show_dm Similar to -show, but also prints the geographic corner coordinates in Degrees and Decimal Minutes.
-show_meta Calculates and displays the geographic coordinates (Lat/Lon) of all four corners of the grid.
-dump_tfw Creates a World File (.tfw) for the grid. This is a standard sidecar file for georeferencing raster images in GIS software.
-dump_geotiff Creates a metadata file (.geo_meta) containing the tags and keys needed to georeference the grid as a proper GeoTIFF.
-dump_esri_grid Creates an ASCII header file (.esri_grid) that is compatible with ESRI’s grid format.
-dump_kml_groundoverlay Creates a KML file (.kml) to display the grid as a ground overlay in Google Earth. Supports rotated grids.
-clamptoseafloor Used with -dump_kml_groundoverlay. Sets the KML altitude mode to clampToSeaFloor, draping the image over the seafloor bathymetry in Google Earth.
-addCentreMark Used with -dump_kml_groundoverlay. Adds a placemark at the center of the KML overlay.
-center When dumping georeferencing info (e.g., -dump_tfw), this specifies that the origin coordinates should refer to the center of the top-left pixel. The default is the top-left corner, which is standard for most GIS software.
-proj_long <longitude> Specifies the projection longitude to be used when exporting georeferencing for Mercator-projected grids. Essential for ensuring correct alignment in external programs.

File Manipulation Options

| Option | Description | |—|—| | -replacehead <source_grid_file> | Copies the header from <source_grid_file> and overwrites the header of the main input grid file. | | -fix_Y | Recalculates the number of rows (dy) in the grid based on the file size and data type, then corrects the header. This is useful for fixing headers of truncated or corrupted files. |

Interactive Mode

If edhead is run with only a filename as an argument, it enters an interactive menu-driven mode. This allows the user to manually change any field in the header, such as:

  • Grid dimensions (dx, dy)
  • Geographic boundaries (ymax, ymin, xmax, xmin)
  • Pixel size (xstep, ystep)
  • Data type (8-bit, 16-bit, float)
  • Projection information
  • Labels and descriptive text

This mode is intended for manual inspection and correction of grid metadata.

How It Works

edhead operates by directly reading and manipulating the JHC_header of the specified grid file.

  • Display Mode: When used with -show or similar flags, it reads the header, converts internal binary representations to human-readable formats (e.g., converting projection codes to names), and prints them to standard output.
  • Export Mode: When used with -dump_tfw, -dump_geotiff, etc., it extracts relevant geographic and projection information from the header and formats it into the specific output file format. This often involves converting internal JHC projection parameters to external standards.
  • Interactive Mode: In interactive mode, it reads the header into memory, presents a menu of editable fields, prompts the user for new values, and then writes the modified header back to the file.
  • File Manipulation: For options like -replacehead or -fix_Y, it performs direct read/write operations on the file’s header block to update or correct metadata.

Output Files

  • Output depends on the selected option:
    • *.tfw: World File.
    • *.geo_meta: GeoTIFF metadata.
    • *.esri_grid: ESRI grid ASCII header.
    • *.kml: Google Earth KML file.
    • The input grid file itself may be modified in place if header manipulation options are used.

Dependencies

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

Notes

edhead is a critical tool for managing and validating the metadata of JHC grid files, ensuring compatibility with other GIS and mapping software. Its interactive mode provides a direct way to correct header errors that might otherwise cause issues in downstream processing.