Add a gallery example for plotting Cartesian, circular and geographic vectors

examples/gallery/line/vectors.py

@@ -0,0 +1,64 @@
+"""
+Cartesian, circular, and geographic vectors
+-------------------------------------------
+
+The :meth:`pygmt.Figure.plot` method can plot Cartesian, circular, and geographic vectors.
+The ``style`` parameter controls vector attributes.
+Vector documentation: https://www.pygmt.org/dev/gallery/line/vector-heads-tails.html
+
+"""
+import numpy as np
+import pygmt
+
+# create a plot with coast, Mercator projection (M) over the continental US
+fig = pygmt.Figure()
+fig.coast(
+    region=[-127, -64, 24, 53],
+    projection="M15c",
+    frame=True,
+    borders=1,
+    area_thresh=4000,
+    shorelines="0.25p,black",
+)
+
+
+# Left: plot 12 Cartesian vectors with different lengths
+x = np.linspace(-116, -116, 12)  # x vector coordinates
+y = np.linspace(33.5, 42.5, 12)  # y vector coordinates
+direction = np.zeros(x.shape)  # direction of vectors
+length = np.linspace(0.5, 2.4, 12)  # length of vectors
+# Cartesian vectors (v) with red pen and fill (+g, +p), vector head at end (+e),
+#   and 40 degree angle with no indentation for vector head (+a, +h)
+style = "v0.2c+e+a40+gred+h0+p1p,red"
+fig.plot(x=x, y=y, style=style, pen="1p,red", direction=[direction, length])
+fig.text(text="CARTESIAN", x=-112, y=44.2, font="13p,Helvetica-Bold,red", fill="white")
+
+
+# Middle: plot 7 math angle arcs with different radii
+num = 7
+x = np.full(num, -95)  # x coordinates of the center
+y = np.full(num, 37)  # y coordinates of the center
+radius = 1.8 - 0.2 * np.arange(0, num)  # radius
+startdir = np.full(num, 90)  # start direction in degrees
+stopdir = 180 + 40 * np.arange(0, num)  # stop direction in degrees
+# data for circular vectors
+data = np.column_stack([x, y, radius, startdir, stopdir])
+arcstyle = "m0.5c+ea"  # Circular vector (m) with an arrow at end
+fig.plot(data=data, style=arcstyle, color="red3", pen="1.5p,black")
+fig.text(text="CIRCULAR", x=-95, y=44.2, font="13p,Helvetica-Bold,black", fill="white")
+
+
+# Right: plot geographic vectors using endpoints
+NYC = [-74.0060, 40.7128]
+CHI = [-87.6298, 41.8781]
+SEA = [-122.3321, 47.6062]
+NO = [-90.0715, 29.9511]
+# `=` means geographic vectors.
+# With the modifier '+s', the input data should contain coordinates of start and end points
+style = "=0.5c+s+e+a30+gblue+h0.5+p1p,blue"
+data = np.array([NYC + CHI, NYC + SEA, NYC + NO])
+fig.plot(data=data, style=style, pen="1.0p,blue")
+fig.text(
+    text="GEOGRAPHIC", x=-74.5, y=44.2, font="13p,Helvetica-Bold,blue", fill="white"
+)
+fig.show()