Add WindBarbs to Matplotlib Backend

examples/gallery/bokeh/orthographic_vectorfield.ipynb

@@ -48,7 +48,7 @@
     "\n",
     "xs, ys, U, V, crs = sample_data()\n",
     "mag = np.sqrt(U**2 + V**2)\n",
-    "angle = (np.pi/2.) - np.arctan2(U/mag, V/mag)\n",
+    "angle = np.pi / 2 - np.arctan2(-V, -U)\n",
     "vectorfield = gv.VectorField((xs, ys, angle, mag), crs=crs)"
    ]
   },

examples/gallery/bokeh/vectorfield_example.ipynb

@@ -47,7 +47,7 @@
     "\n",
     "xs, ys, U, V, crs = sample_data()\n",
     "mag = np.sqrt(U**2 + V**2)\n",
-    "angle = (np.pi/2.) - np.arctan2(U/mag, V/mag)\n",
+    "angle = np.pi / 2 - np.arctan2(-V, -U)\n",
     "tiles = gv.tile_sources.OSM\n",
     "vectorfield = gv.VectorField((xs, ys, angle, mag), crs=crs)"
    ]

examples/gallery/matplotlib/orthographic_vectorfield.ipynb

@@ -50,7 +50,7 @@
     "\n",
     "xs, ys, U, V, crs = sample_data()\n",
     "mag = np.sqrt(U**2 + V**2)\n",
-    "angle = (np.pi/2.) - np.arctan2(U/mag, V/mag)\n",
+    "angle = np.pi / 2 - np.arctan2(-V, -U)\n",
     "vectorfield = gv.VectorField((xs, ys, angle, mag), crs=crs)"
    ]
   },

examples/gallery/matplotlib/vectorfield_example.ipynb

@@ -49,7 +49,7 @@
     "\n",
     "xs, ys, U, V, crs = sample_data()\n",
     "mag = np.sqrt(U**2 + V**2)\n",
-    "angle = (np.pi/2.) - np.arctan2(U/mag, V/mag)\n",
+    "angle = np.pi / 2 - np.arctan2(-V, -U)\n",
     "tiles = gv.tile_sources.OSM\n",
     "vectorfield = gv.VectorField((xs, ys, angle, mag), crs=crs)"
    ]

examples/gallery/matplotlib/wind_barbs_example.ipynb

@@ -0,0 +1,90 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import numpy as np\n",
+    "import geoviews as gv\n",
+    "\n",
+    "gv.extension('matplotlib')\n",
+    "\n",
+    "gv.output(fig='svg', size=200)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Define data"
+   ]
+  },
+  {
+   "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",
+    "wind_barbs = gv.WindBarbs.from_uv((lon, lat, uwnd, vwwnd)).opts(\n",
+    "    fig_size=250, length=6.5, padding=1\n",
+    ")\n",
+    "coastline = gv.feature.coastline()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Plot"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "wind_barbs * coastline"
+   ]
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python",
+   "pygments_lexer": "ipython3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

geoviews/__init__.py

@@ -11,7 +11,7 @@
     _Element, Feature, Tiles, WMTS, LineContours, FilledContours,
     Text, Image, Points, Path, Polygons, Shape, Dataset, RGB,
     Contours, Graph, TriMesh, Nodes, EdgePaths, QuadMesh, VectorField,
-    HexTiles, Labels, Rectangles, Segments
+    HexTiles, Labels, Rectangles, Segments, WindBarbs
 )
 from .util import load_tiff, from_xarray # noqa (API import)
 from .operation import project                      # noqa (API import)

geoviews/element/__init__.py

@@ -7,7 +7,7 @@
                   WMTS, Points, Image, Text, LineContours, RGB,
                   FilledContours, Path, Polygons, Shape, Dataset,
                   Contours, TriMesh, Graph, Nodes, EdgePaths, QuadMesh,
-                  VectorField, Labels, HexTiles, Rectangles, Segments)
+                  VectorField, Labels, HexTiles, Rectangles, Segments, WindBarbs)
 
 
 class GeoConversion(ElementConversion):

geoviews/element/comparison.py

@@ -2,7 +2,7 @@
 
 from holoviews.element.comparison import Comparison as HvComparison
 
-from .geo import Image, Points, LineContours, FilledContours
+from .geo import Image, Points, LineContours, FilledContours, WindBarbs
 
 class Comparison(HvComparison):
 
@@ -13,6 +13,7 @@ def register(cls):
         cls.equality_type_funcs[Points] = cls.compare_dataset
         cls.equality_type_funcs[LineContours] = cls.compare_dataset
         cls.equality_type_funcs[FilledContours] = cls.compare_dataset
+        cls.equality_type_funcs[WindBarbs] = cls.compare_dataset
         return cls.equality_type_funcs
 
 

geoviews/element/geo.py

@@ -15,8 +15,10 @@
     QuadMesh as HvQuadMesh, Points as HvPoints,
     VectorField as HvVectorField, HexTiles as HvHexTiles,
     Labels as HvLabels, Rectangles as HvRectangles,
-    Segments as HvSegments
+    Segments as HvSegments, Geometry as HvGeometry,
 )
+from holoviews.element.selection import Selection2DExpr
+
 
 from shapely.geometry.base import BaseGeometry
 from shapely.geometry import (
@@ -340,6 +342,42 @@ class VectorField(_Element, HvVectorField):
                                 Dimension('Magnitude')], bounds=(1, None))
 
 
+class WindBarbs(_Element, Selection2DExpr, HvGeometry):
+    """
+    """
+
+    group = param.String(default='WindBarbs', constant=True)
+
+    vdims = param.List(default=[Dimension('Angle', cyclic=True, range=(0,2*np.pi)),
+                                Dimension('Magnitude')], bounds=(2, None))
+
+    @classmethod
+    def from_uv(cls, data, kdims=None, vdims=None, **params):
+        if isinstance(data, tuple):
+            xs, ys, us, vs = data
+        else:
+            us = data[vdims[0]]
+            vs = data[vdims[1]]
+
+        uv_magnitudes = np.hypot(us, vs)  # unscaled
+        radians = np.pi / 2 - np.arctan2(-vs, -us)
+
+        if isinstance(data, tuple):
+            reorganized_data = (xs, ys, radians, uv_magnitudes)
+        else:
+            # calculations on this data could mutate the original data
+            # here we do not do any calculations; we only store the data
+            reorganized_data = {}
+            for kdim in kdims:
+                reorganized_data[kdim] = data[kdim]
+            reorganized_data["Angle"] = radians
+            reorganized_data["Magnitude"] = uv_magnitudes
+            for vdim in vdims[2:]:
+                reorganized_data[vdim] = data[vdim]
+            vdims = ["Angle", "Magnitude"] + vdims[2:]
+        return cls(reorganized_data, kdims=kdims, vdims=vdims, **params)
+
+
 class Image(_Element, HvImage):
     """
     Image represents a 2D array of some quantity with

geoviews/plotting/mpl/__init__.py

@@ -30,7 +30,7 @@
     Image, Points, Feature, WMTS, Tiles, Text, LineContours,
     FilledContours, is_geographic, Path, Polygons, Shape, RGB,
     Contours, Nodes, EdgePaths, Graph, TriMesh, QuadMesh, VectorField,
-    HexTiles, Labels, Rectangles, Segments
+    HexTiles, Labels, Rectangles, Segments, WindBarbs
 )
 from ...util import geo_mesh, poly_types
 from ..plot import ProjectionPlot
@@ -39,6 +39,7 @@
     project_points, project_path, project_graph, project_quadmesh,
     project_geom
 )
+from .chart import WindBarbsPlot
 
 
 
@@ -327,6 +328,16 @@ class GeoVectorFieldPlot(GeoPlot, VectorFieldPlot):
     _project_operation = project_points
 
 
+class GeoWindBarbsPlot(GeoPlot, WindBarbsPlot):
+    """
+    Draws a wind barbs plot from the data in a WindBarbs Element.
+    """
+
+    apply_ranges = param.Boolean(default=True)
+
+    _project_operation = project_points
+
+
 class GeometryPlot(GeoPlot):
 
     def init_artists(self, ax, plot_args, plot_kwargs):
@@ -567,6 +578,7 @@ def draw_annotation(self, axis, data, crs, opts):
                 Points: GeoPointPlot,
                 Labels: GeoLabelsPlot,
                 VectorField: GeoVectorFieldPlot,
+                WindBarbs: GeoWindBarbsPlot,
                 Text: GeoTextPlot,
                 Layout: LayoutPlot,
                 NdLayout: LayoutPlot,