Clipping grid values

The pygmt.grdclip function 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.

grdblend [NOTICE]: Remote data courtesy of GMT data server oceania [http://oceania.generic-mapping-tools.org]
grdblend [NOTICE]: SRTM15 Earth Relief v2.5.5 at 03x03 arc minutes reduced by Gaussian Cartesian filtering (15.7 km fullwidth) [Tozer et al., 2019].
grdblend [NOTICE]:   -> Download 90x90 degree grid tile (earth_relief_03m_g): N00W090

import pygmt

fig = pygmt.Figure()

# Define region of interest around Iceland
region = [-28, -10, 62, 68]

# Load sample grid (3 arc-minutes 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=["WSne+toriginal grid", "xa5f1", "ya2f1"],
)
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=["wSne+tclipped grid", "xa5f1", "ya2f1"],
)
fig.grdimage(grid=grid)
fig.colorbar(frame=["x+lElevation", "y+lm"], position="JMR+o0.5c/0c+w8c")

fig.show()