Sampling along tracks

The pygmt.grdtrack function samples a raster grid’s value along specified points. We will need to input a 2D raster to grid which can be an xarray.DataArray. The argument passed to the points parameter can be a pandas.DataFrame table where the first two columns are x and y (or longitude and latitude). Note also that there is a newcolname parameter that will be used to name the new column of values sampled from the grid.

Alternatively, a NetCDF file path can be passed to grid. An ASCII file path can also be accepted for points. To save an output ASCII file, a file name argument needs to be passed to the outfile parameter.

gmtwhich [NOTICE]: Remote data courtesy of GMT data server oceania [http://oceania.generic-mapping-tools.org]
gmtwhich [NOTICE]: SRTM15 Earth Relief at 1x1 arc degrees reduced by Gaussian Cartesian filtering (111.2 km fullwidth) [Tozer et al., 2019].
gmtwhich [NOTICE]:   -> Download grid file [114K]: earth_relief_01d_p.grd
<IPython.core.display.Image object>

import pygmt

# Load sample grid and point datasets
grid = pygmt.datasets.load_earth_relief()
points = pygmt.datasets.load_sample_data(name="ocean_ridge_points")
# Sample the bathymetry along the world's ocean ridges at specified track
# points
track = pygmt.grdtrack(points=points, grid=grid, newcolname="bathymetry")

fig = pygmt.Figure()
# Plot the earth relief grid on Cylindrical Stereographic projection, masking
# land areas
fig.basemap(region="g", projection="Cyl_stere/150/-20/15c", frame=True)
fig.grdimage(grid=grid, cmap="gray")
fig.coast(land="#666666")
# Plot the sampled bathymetry points using circles (c) of 0.15 cm size
# Points are colored using elevation values (normalized for visual purposes)
fig.plot(
    x=track.longitude,
    y=track.latitude,
    style="c0.15c",
    cmap="terra",
    color=(track.bathymetry - track.bathymetry.mean()) / track.bathymetry.std(),
)
fig.show()