Improved handling of non-default central longitudes

examples/gallery/bokeh/filled_contours.ipynb

@@ -46,7 +46,9 @@
     "    return lons, lats, data\n",
     "\n",
     "lons, lats, data = sample_data()\n",
-    "contours = hv.operation.contours(gv.Image((lons, lats, data)), filled=True, levels=8).redim.range(z=(-1.1, 1.1))"
+    "\n",
+    "# Make sure we declare the central longitude\n",
+    "contours = gv.FilledContours((lons, lats, data), crs=crs.PlateCarree(central_longitude=180))"
    ]
   },
   {
@@ -63,7 +65,7 @@
    "outputs": [],
    "source": [
     "(contours * gf.coastline).opts(\n",
-    "    opts.Polygons(colorbar=True, width=600, height=300, color_levels=10, projection=crs.Mollweide(), cmap='nipy_spectral'))"
+    "    opts.FilledContours(levels=8, color_levels=10, cmap='nipy_spectral', colorbar=True, width=600, height=300, projection=crs.Mollweide()))"
    ]
   }
  ],

examples/gallery/matplotlib/filled_contours.ipynb

@@ -45,7 +45,9 @@
     "    return lons, lats, data\n",
     "\n",
     "lons, lats, data = sample_data()\n",
-    "contours = gv.FilledContours((lons, lats, data))"
+    "\n",
+    "# Make sure we declare the central longitude\n",
+    "contours = gv.FilledContours((lons, lats, data), crs=ccrs.PlateCarree(central_longitude=180))"
    ]
   },
   {
@@ -61,7 +63,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "contours.opts(projection=ccrs.Mollweide(), cmap='nipy_spectral') * gf.coastline"
+    "contours.opts(colorbar=True, levels=8, color_levels=10, cmap='nipy_spectral', projection=ccrs.Mollweide()) * gf.coastline"
    ]
   }
  ],

examples/user_guide/Projections.ipynb

@@ -174,7 +174,31 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "features.opts(projection=crs.Orthographic(central_longitude=0, central_latitude=30), global_extent=True)"
+    "features.opts(projection=crs.Orthographic(central_longitude=-90, central_latitude=30), global_extent=True)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "This is particularly important when the data is specified in the longitudes of the data are defined in the range 0 to 360 rather than the default -180 to 180. In this case ensure that the ``crs`` of the element declares the actual ``central_longitude``, e.g. 180 degrees rather than the default 0 degrees. Let us draw the same polygon with the default ``crs`` (centered on 0) and a custom ``crs`` centered on 180 degrees:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "poly_data = [(180, 0), (270, 45), (360, 0)]\n",
+    "features * gv.Polygons(poly_data) * gv.Polygons(poly_data, crs=crs.PlateCarree(central_longitude=180)).opts(global_extent=True)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "As we can see the default projection wraps the values above 180, while the custom projection automatically translates the polygon by the ``central_longitude``."
    ]
   },
   {

examples/user_guide/Resampling_Grids.ipynb

@@ -253,8 +253,6 @@
    "outputs": [],
    "source": [
     "ds = xr.tutorial.open_dataset('rasm').load()\n",
-    "# Adjust the longitudes so they are in the range -180 to 180\n",
-    "ds.xc.values[ds.xc.values>180] -= 360 \n",
     "ds"
    ]
   },

geoviews/operation/projection.py

@@ -1,13 +1,12 @@
 import logging
 
 import param
-import shapely
 import numpy as np
 
 from cartopy import crs as ccrs
 from cartopy.img_transform import warp_array, _determine_bounds
 from holoviews.core.data import MultiInterface
-from holoviews.core.util import cartesian_product, get_param_values, max_extents, pd
+from holoviews.core.util import cartesian_product, get_param_values, pd
 from holoviews.operation import Operation
 from shapely.geometry import Polygon, MultiPolygon
 from shapely.geometry.collection import GeometryCollection
@@ -49,37 +48,28 @@ class project_path(_project_operation):
     supported_types = [Polygons, Path, Contours, EdgePaths]
 
     def _process_element(self, element):
-        if not len(element):
+        if not bool(element):
             return element.clone(crs=self.p.projection)
 
         crs = element.crs
-        cylindrical = isinstance(crs, ccrs._CylindricalProjection)
         proj = self.p.projection
+        if (isinstance(crs, ccrs.PlateCarree) and not isinstance(proj, ccrs.PlateCarree)
+            and crs.proj4_params['lon_0'] != 0):
+            element = self.instance(projection=ccrs.PlateCarree())(element)
+
         if isinstance(proj, ccrs.CRS) and not isinstance(proj, ccrs.Projection):
             raise ValueError('invalid transform:'
                              ' Spherical contouring is not supported - '
                              ' consider using PlateCarree/RotatedPole.')
 
-        boundary = Polygon(crs.boundary)
-        bounds = [round(b, 10) for b in boundary.bounds]
-        xoffset = round((boundary.bounds[2]-boundary.bounds[0])/2.)
         if isinstance(element, Polygons):
             geoms = polygons_to_geom_dicts(element, skip_invalid=False)
         else:
             geoms = path_to_geom_dicts(element, skip_invalid=False)
 
-        data_bounds = max_extents([g['geometry'].bounds for g in geoms])
-        total_bounds = tuple(round(b, 10) for b in data_bounds)
-
         projected = []
         for path in geoms:
             geom = path['geometry']
-            if (cylindrical and total_bounds[0] >= (bounds[0]+xoffset) and
-                total_bounds[2] > (bounds[2]+xoffset//2) and
-                total_bounds[2] <= bounds[2]+xoffset):
-                # Offset if lon and not centered on 0 longitude
-                # i.e. lon_min > 0 and lon_max > 270
-                geom = shapely.affinity.translate(geom, xoff=-xoffset)
 
             # Ensure minimum area for polygons (precision issues cause errors)
             if isinstance(geom, Polygon) and geom.area < 1e-15:
@@ -313,6 +303,10 @@ def _process(self, img, key=None):
             else:
                 projected, extents = arr, trgt_ext
             arrays.append(projected)
+
+        if xn == 0 or yn == 0:
+            return img.clone([], bounds=extents, crs=proj)
+
         xunit = ((extents[1]-extents[0])/float(xn))/2.
         yunit = ((extents[3]-extents[2])/float(yn))/2.
         xs = np.linspace(extents[0]+xunit, extents[1]-xunit, xn)

geoviews/util.py

@@ -28,6 +28,14 @@ def wrap_lons(lons, base, period):
 def project_extents(extents, src_proj, dest_proj, tol=1e-6):
     x1, y1, x2, y2 = extents
 
+    if (isinstance(src_proj, ccrs.PlateCarree) and
+        not isinstance(dest_proj, ccrs.PlateCarree) and
+        src_proj.proj4_params['lon_0'] != 0):
+        xoffset = src_proj.proj4_params['lon_0']
+        x1 = x1 - xoffset
+        x2 = x2 - xoffset
+        src_proj = ccrs.PlateCarree()
+
     # Limit latitudes
     cy1, cy2 = src_proj.y_limits
     if y1 < cy1: y1 = cy1

setup.py

@@ -129,7 +129,7 @@ def package_assets(example_path):
 _required = [
     'bokeh >=1.0.0',
     'cartopy >=0.16.0',  # prevents pip alone (requires external package manager)
-    'holoviews >=1.11.0',
+    'holoviews >=1.11.1',
     'numpy >=1.0',
     'param >=1.6.1'
 ]