Add gallery example for grdclip (#1396)

Co-authored-by: Dongdong Tian <[email protected]>

Author: michaelgrund

examples/gallery/images/grdclip.py

@@ -0,0 +1,36 @@
+"""
+Clipping grid values
+--------------------
+The :meth:`pygmt.grdclip` method allows to clip defined ranges of grid values.
+In the example shown below we set all elevation values (grid points) smaller
+than 0 m (in general the bathymetric part of the grid) to a common value of
+-2000 m via the ``below`` parameter.
+"""
+
+import pygmt
+
+fig = pygmt.Figure()
+
+# Define region of interest around Iceland
+region = [-28, -10, 62, 68]
+
+# Load sample grid (3 arc minute global relief) in target area
+grid = pygmt.datasets.load_earth_relief(resolution="03m", region=region)
+
+# Plot original grid
+fig.basemap(region=region, projection="M12c", frame=["f", '+t"original grid"'])
+fig.grdimage(grid=grid, cmap="oleron")
+
+# Shift plot origin of the second map by "width of the first map + 0.5 cm"
+# in x direction
+fig.shift_origin(xshift="w+0.5c")
+
+# Set all grid points < 0 m to a value of -2000 m.
+grid = pygmt.grdclip(grid, below=[0, -2000])
+
+# Plot clipped grid
+fig.basemap(region=region, projection="M12c", frame=["f", '+t"clipped grid"'])
+fig.grdimage(grid=grid)
+fig.colorbar(frame=["x+lElevation", "y+lm"], position="JMR+o0.5c/0c+w8c")
+
+fig.show()