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layout: default title: convertSectionUVtoRadTan parent: Grid Tools nav_order: 14 —

convertSectionUVtoRadTan

Description

convertSectionUVtoRadTan is a command-line utility designed to transform gridded U (eastward) and V (northward) velocity components, typically from an ocean model or ADCP data, into along-section and across-section velocity components. It specifically works with data representing a 2D cross-section extracted from a 3D model (e.g., using extractVertSection). It requires the U and V velocity grids and a separate ASCII file containing the azimuth of the profile at each point along the section. The output is three new JHC-format 32-bit floating-point (.r4) grids: one for along-section velocity, one for across-section velocity, and one for the current magnitude.

Usage

convertSectionUVtoRadTan -prefix <SectionPath/SectionPrefix> [OPTIONS]

Arguments

Option	Description	Default / Example
-prefix <SectionPath/SectionPrefix>	Required. Specifies the base path and prefix for the input velocity and azimuth files. The tool expects: - <prefix>.uVelocity.r4 (U-velocity) - <prefix>.vVelocity.r4 (V-velocity) - <prefix>.uVelocity.llazi (profile azimuths). Output files will be named: - <prefix>.AlongVel.r4 - <prefix>.AcrossVel.r4 - <prefix>.cMagnitude.r4	-prefix SalishSea_Data/Converted/Section_A/section_profile
-testrot	Enables an interactive test mode where the user can manually input U, V, and azimuth values to see the calculated along-section and across-section components.
-v	Enable verbose output during processing.

How It Works

1. File Opening: Opens the input .r4 grids for U-velocity and V-velocity, and the ASCII file for profile azimuths. Creates three new .r4 grids for along-section velocity, across-section velocity, and current magnitude.
2. Header Reading: Reads the JHC_header from the input .r4 files, ensuring dimensions match.
3. Data Processing: Iterates through each grid cell:
   • Reads u_velocity and v_velocity from the respective grids.
   • Reads profile_azimuth from the azimuth file.
   • Calculates current_magnitude from u_velocity and v_velocity.
   • Calculates along_section_velocity and across_section_velocity by rotating the U and V components into the coordinate system defined by profile_azimuth.
   • Writes these three calculated values to their respective output .r4 grids.
4. testrot Mode: If -testrot is enabled, it provides an interactive prompt to input U, V, and azimuth values and displays the calculated radial and tangential components.

Output Files

• <prefix>.AlongVel.r4: JHC-format .r4 grid for along-section velocity.
• <prefix>.AcrossVel.r4: JHC-format .r4 grid for across-section velocity.
• <prefix>.cMagnitude.r4: JHC-format .r4 grid for current magnitude.

Dependencies

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

Notes

This tool is crucial for analyzing current patterns in ocean models or ADCP data along specific transects. By transforming the velocities into along-section and across-section components, it simplifies the interpretation of flow dynamics relative to the section orientation.