DOC: Use the EU flag image from the GMT data server in the 'Draping on 3-D surface' example (#4432)

Author: seisman

examples/tutorials/advanced/draping_on_3d_surface.py

@@ -8,7 +8,6 @@
 This tutorial consists of two examples:
 
 1. Draping a grid
-
 2. Draping an image
 """
 
@@ -53,7 +52,7 @@
 pygmt.makecpt(cmap="SCM/batlow", series=[0, 200, 1], reverse=True, overrule_bg=True)
 
 fig.grdview(
-    projection="M12c",  # Mercator projection with a width of 12 centimeters
+    projection="M12c",  # Mercator projection with a width of 12 cm
     region=region_3d,
     grid=grd_relief,  # Use elevation grid for z values
     drape_grid=grd_age,  # Use crustal age grid for color-coding
@@ -96,9 +95,11 @@
 # Determine the 3-D region from the minimum and maximum values of the relief grid
 region_3d = [*region_2d, grd_relief.min().to_numpy(), grd_relief.max().to_numpy()]
 
-# Download an PNG image of the flag of the EU using rasterio and load it into a
-# xarray.DataArray
-url_to_image = "https://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Flag_of_Europe.svg/1024px-Flag_of_Europe.svg.png"
+# Load a PNG image of the EU flag using rasterio into an xarray.DataArray.
+# The original image is available on Wikimedia Commons at
+# https://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Flag_of_Europe.svg/1024px-Flag_of_Europe.svg.png
+# but we use a cached version on the GMT data server.
+url_to_image = "https://oceania.generic-mapping-tools.org/cache/euflag.png"
 with rasterio.open(url_to_image) as dataset:
     data = dataset.read()
     drape_grid = xr.DataArray(data, dims=("band", "y", "x"))
@@ -117,7 +118,7 @@
 pygmt.makecpt(cmap="0/51/153,255/204/0", series=[0, 256, 128])
 
 fig.grdview(
-    projection="M12c",  # Mercator projection with a width of 12 centimeters
+    projection="M12c",  # Mercator projection with a width of 12 cm
     region=region_3d,
     grid=grd_relief,  # Use elevation grid for z values
     drape_grid=drape_grid,  # Drape image grid for the EU flag on top
@@ -126,7 +127,7 @@
     # Use an illumination from the azimuthal directions 0° (north) and 270° (west) with
     # a normalization via a cumulative Laplace distribution for the shading
     shading="+a0/270+ne0.6",
-    perspective=[157.5, 30],  # Define azimuth, elevation for the 3-D plot
+    perspective=(157.5, 30),  # Define azimuth, elevation for the 3-D plot
     zsize="1c",
     facade_fill="darkgray",
     frame=True,