layout: default title: combineSeaCast parent: Grid Tools nav_order: 11 —

combineSeaCast

Description

combineSeaCast is a command-line utility that processes gridded output from an oceanographic model (likely SeaCast, given the name) to derive current magnitude and azimuth. It takes four JHC-format 32-bit floating-point (.r4) grid files as input: latitude, longitude, U-velocity (eastward), and V-velocity (northward). It then calculates the vector magnitude and direction (azimuth) for the current at each grid node and outputs these as a series of JCU navigation records (latitude, longitude, magnitude, azimuth) to an ASCII file, suitable for plotting as vectors on a map.

Usage 

combineSeaCast -lat <file_lat.r4> -lon <file_lon.r4> -uvel <file_uvel.r4> -vvel <file_vvel.r4> -out <output.nav> [OPTIONS]

Arguments

Option Description Default / Example
-lat <file_lat.r4> Required. Path to the JHC-format .r4 grid file containing latitude values for each grid node. lat_grid.r4
-lon <file_lon.r4> Required. Path to the JHC-format .r4 grid file containing longitude values for each grid node. lon_grid.r4
-uvel <file_uvel.r4> Required. Path to the JHC-format .r4 grid file containing eastward (U) velocity components for each grid node. u_velocity.r4
-vvel <file_vvel.r4> Required. Path to the JHC-format .r4 grid file containing northward (V) velocity components for each grid node. v_velocity.r4
-out <output.nav> Required. Path for the output JCU navigation format file, containing latitude, longitude, current magnitude, and azimuth for each grid node. current_vectors.nav
-v Enable verbose output during processing.  

How It Works

  1. File Opening: Opens the four input .r4 grid files (latitude, longitude, U-velocity, V-velocity) and the output .nav file.
  2. Header Reading: Reads the JHC_header from the input files, ensuring their dimensions match.
  3. Pixel Iteration: Iterates through each corresponding pixel in the input grids:
    • Reads latitude, longitude, u_velocity, and v_velocity for the current grid node.
    • Calculates the magnitude of the current vector: sqrt(u_velocity^2 + v_velocity^2).
    • Calculates the azimuth of the current vector: atan2(u_velocity, v_velocity).
    • Populates a jcu_nav_rec structure with latitude, longitude, magnitude, and azimuth.
    • Writes the jcu_nav_rec to the output .nav file.

Output Files

  • <output.nav>: An ASCII file in JCU navigation format, where each record contains latitude, longitude, current magnitude, and azimuth.

Dependencies

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

Notes

The output .nav file can be directly used by plotting tools that support the JCU navigation format to visualize current vectors overlaid on a map. This tool is valuable for converting model output into a readily plottable format for oceanographic analysis.