{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import geoviews as gv\n",
    "\n",
    "gv.extension('bokeh')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Define data\n",
    "\n",
    "IMPORTANT:\n",
    "\n",
    "Unlike the `VectorField` direction, which follows the mathematical convention:\n",
    "\n",
    "Reference: 0° = East (positive x-axis)\n",
    "Direction: Counterclockwise\n",
    "Meaning: Direction the vector points to\n",
    "Formula: θ = arctan2(v, u)\n",
    "\n",
    "```\n",
    "        N (90°)\n",
    "         |\n",
    "W (180°)-+-E (0°)\n",
    "         |\n",
    "        S (270°)\n",
    "```\n",
    "\n",
    "The `WindBarbs` direction follows the meteorological convention:\n",
    "\n",
    "Reference: 0° = North\n",
    "Direction: Clockwise\n",
    "Meaning: Direction the wind is coming from\n",
    "Formula: θ = 90° - arctan2(-v, -u)\n",
    "\n",
    "```\n",
    "        N (0°/360°)\n",
    "         |\n",
    "W (270°)-+-E (90°)\n",
    "         |\n",
    "        S (180°)\n",
    "```\n",
    "\n",
    "For convenience, `from_uv` can be used to create a `WindBarbs` directly from U/V components to use the meteorological conventions."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "lat = np.arange(60, 37.5, -2.5)\n",
    "lon = np.arange(270, 292.5, 2.5)\n",
    "uwnd = np.array(\n",
    "    [\n",
    "        [2, 0, -2, -2, -3, -3, -3, -2, -1],\n",
    "        [2, 0, -2, -2, -2, -2, -2, -1, 1],\n",
    "        [2, -1, -2, -2, -2, -1, 0, 1, 3],\n",
    "        [3, 0, -3, -5, -5, -4, -4, -2, 0],\n",
    "        [8, 4, 0, -3, -5, -6, -6, -6, -5],\n",
    "        [12, 10, 8, 5, 3, 0, -2, -2, -2],\n",
    "        [13, 14, 16, 16, 14, 12, 10, 9, 10],\n",
    "        [13, 18, 22, 24, 25, 24, 23, 22, 23],\n",
    "        [20, 25, 29, 32, 33, 32, 32, 33, 34],\n",
    "    ]\n",
    ")\n",
    "vwwnd = np.array(\n",
    "    [\n",
    "        [3, 1, 0, -1, -1, 0, 1, 3, 4],\n",
    "        [-2, -3, -3, -2, 0, 2, 4, 6, 8],\n",
    "        [-6, -6, -4, -1, 2, 5, 7, 10, 12],\n",
    "        [-12, -10, -6, -1, 4, 7, 10, 12, 14],\n",
    "        [-17, -15, -10, -4, 2, 6, 9, 12, 16],\n",
    "        [-20, -18, -14, -8, -2, 2, 5, 10, 16],\n",
    "        [-17, -16, -13, -9, -6, -3, 1, 7, 15],\n",
    "        [-11, -10, -8, -6, -6, -5, -2, 6, 15],\n",
    "        [-5, -3, -2, -2, -4, -5, -2, 6, 15],\n",
    "    ]\n",
    ")\n",
    "\n",
    "# equivalent to metpy.calc.wind_direction(uwnd, vwwnd).to(\"radian\")\n",
    "wdir = np.pi / 2 - np.arctan2(-vwwnd, -uwnd)\n",
    "wspd = np.sqrt(uwnd**2 + vwwnd**2)\n",
    "\n",
    "wind_barbs = gv.WindBarbs((lon, lat, wdir, wspd)).opts(\n",
    "    width=500, height=500, padding=0.5, title=\"Wind Barbs from direction/speed\"\n",
    ")\n",
    "wind_barbs_from_uv = gv.WindBarbs.from_uv((lon, lat, uwnd, vwwnd)).opts(\n",
    "    width=500, height=500, padding=0.5, title=\"Wind Barbs from U/V components\"\n",
    ")\n",
    "coastline = gv.feature.coastline()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Plot"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "wind_barbs * coastline + wind_barbs_from_uv * coastline"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Alternatively, `WindBarbs` can be adapted to oceanography convention:\n",
    "\n",
    "- Takes the direction the fluid is moving\n",
    "\n",
    "- But uses North = 0° and clockwise (like meteorology)\n",
    "\n",
    "- It's 180° opposite from meteorological convention"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "wind_barbs_ocean = gv.WindBarbs((lon, lat, wdir, wspd)).opts(\n",
    "    width=500, height=500, padding=0.5, title=\"Wind Barbs from direction/speed\", convention=\"to\"\n",
    ")\n",
    "wind_barbs_from_uv_ocean = gv.WindBarbs.from_uv((lon, lat, uwnd, vwwnd)).opts(\n",
    "    width=500, height=500, padding=0.5, title=\"Wind Barbs from U/V components\", convention=\"to\"\n",
    ")\n",
    "wind_barbs_from_uv_ocean * coastline + wind_barbs_ocean * coastline"
   ]
  }
 ],
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