Add a gallery example showing different front styles (GenericMappingT…

…ools#1022)

* Add a gallery example showing different line front styles

Co-authored-by: Dongdong Tian <[email protected]>
Co-authored-by: Yao Jiayuan <[email protected]>
Co-authored-by: Will Schlitzer <[email protected]>

examples/gallery/lines/linefronts.py

@@ -0,0 +1,84 @@
+"""
+Line fronts
+-----------
+
+Using the :meth:`pygmt.Figure.plot` method you can draw a so-called
+*front* which allows to plot specific symbols distributed along a line
+or curve. Typical use cases are weather fronts, fault lines,
+subduction zones, and more.
+
+A front can be drawn by passing **f**\[±]\ *gap*\[/*size*] to the ``style``
+parameter where *gap* defines the distance gap between the symbols and
+*size* the symbol size. If *gap* is negative, it is interpreted to mean
+the number of symbols along the front instead. If *gap* has a leading +
+then we use the value exactly as given [Default will start and end each
+line with a symbol, hence the *gap* is adjusted to fit]. If *size* is
+missing it is set to 30% of the *gap*, except when *gap* is negative
+and *size* is thus required. Append **+l** or **+r** to plot symbols on
+the left or right side of the front [Default is centered]. Append
+**+**\ *type* to specify which symbol to plot: **b**\ ox, **c**\ ircle,
+**f**\ ault (default), **s**\ lip, or **t**\ riangle. Slip means left-lateral
+or right-lateral strike-slip arrows (centered is not an option). The **+s**
+modifier optionally accepts the angle used to draw the vector (default is
+20). Alternatively, use **+S** which draws arcuate arrow heads. Append
+**+o**\ *offset* to offset the first symbol from the beginning of the front
+by that amount (default is 0). The chosen symbol is drawn with the same pen
+as set for the line (i.e., via the ``pen`` parameter). To use an alternate
+pen, append **+p**\ *pen*. To skip the outline, just use **+p** with no
+argument. To make the main front line invisible, add **+i**.
+
+"""
+
+import numpy as np
+import pygmt
+
+# Generate a two-point line for plotting
+x = np.array([1, 4])
+y = np.array([20, 20])
+
+fig = pygmt.Figure()
+fig.basemap(region=[0, 10, 0, 20], projection="X15c/15c", frame='+t"Line Fronts"')
+
+# Plot the line using different front styles
+for frontstyle in [
+    # line with "faults" front style, same as +f (default)
+    "f1c/0.25c",
+    # line with box front style
+    "f1c/0.25c+b",
+    # line with circle front style
+    "f1c/0.25c+c",
+    # line with triangle front style
+    "f1c/0.3c+t",
+    # line with left-lateral ("+l") slip ("+s") front style, angle is set to 45 and
+    # offset to 2.25 cm
+    "f5c/1c+l+s45+o2.25c",
+    # line with "faults" front style, symbols are plotted on the left side of the front
+    "f1c/0.4c+l",
+    # line with box front style, symbols are plotted on the left side of the front
+    "f1c/0.3c+l+b",
+    # line with circle front style, symbols are plotted on the right side of the front
+    "f1c/0.4c+r+c",
+    # line with triangle front style, symbols are plotted on the left side of the front
+    "f1c/0.3c+l+t",
+    # line with triangle front style, symbols are plotted on the right side of the front
+    # use other pen for the outline of the symbol
+    "f1c/0.4c+r+t+p1.5p,dodgerblue",
+    # line with triangle front style, symbols are plotted on the right side of the front
+    # and offset is set to 0.3 cm, skip the outline
+    "f0.5c/0.3c+r+t+o0.3c+p",
+    # line with triangle front style, symbols are plotted on the right side of the front
+    # and offset is set to 0.3 cm, skip the outline and make the main front line invisible
+    "f0.5c/0.3c+r+t+o0.3c+p+i",
+]:
+    y -= 1  # move the current line down
+    fig.plot(x=x, y=y, pen="1.25p", style=frontstyle, color="red3")
+    fig.text(
+        x=x[-1],
+        y=y[-1],
+        text=frontstyle,
+        font="Courier-Bold",
+        justify="ML",
+        offset="0.75c/0c",
+    )
+
+fig.show()