Bathymetry — shaded relief¶

Render a GEBCO 2020 subset of the Mid-Atlantic Ridge near the Azores as a hillshaded relief map. Hillshading turns a flat depth grid into an intuitive 3D-looking surface that makes the rift valley and transform faults pop — exactly how a marine geologist would eyeball seafloor structure.

In [ ]:

import tempfile

import numpy as np
from matplotlib import colormaps
from matplotlib.colors import LinearSegmentedColormap
from pyramids.dataset import Dataset
from pyramids.plot import ColorBar, ColorScaling, DataStyle

from earthlens.core import EarthLens

import tempfile import numpy as np from matplotlib import colormaps from matplotlib.colors import LinearSegmentedColormap from pyramids.dataset import Dataset from pyramids.plot import ColorBar, ColorScaling, DataStyle from earthlens.core import EarthLens

In [ ]:

out = tempfile.mkdtemp()
paths = EarthLens(
    data_source='gebco',
    dataset='gebco_2020',
    aoi=[-29.5, 36.2, -27.7, 38.0],
    path=out,
).download(progress_bar=False)

source = Dataset.read_file(paths[0])

stats = source.stats(approx_ok=False)
print(
    'grid',
    source.shape,
    '| depth range',
    round(float(stats['min'].iloc[0])),
    '..',
    round(float(stats['max'].iloc[0])),
    'm',
)

out = tempfile.mkdtemp() paths = EarthLens( data_source='gebco', dataset='gebco_2020', aoi=[-29.5, 36.2, -27.7, 38.0], path=out, ).download(progress_bar=False) source = Dataset.read_file(paths[0]) stats = source.stats(approx_ok=False) print( 'grid', source.shape, '| depth range', round(float(stats['min'].iloc[0])), '..', round(float(stats['max'].iloc[0])), 'm', )

Hillshade¶

Light from the NW (azdeg=315) at 45 degrees elevation; dx/dy are the approximate metres-per-pixel of a 15-arcsec grid, giving the hillshade a physically correct horizontal scale. The vertical axis is a different story: vert_exag=30.0 stretches depth 30x relative to that horizontal scale. This subset of the Mid-Atlantic Ridge is roughly 180 km across but only a few km deep (see the printed depth range above), so a literal vert_exag=1.0 renders the seafloor as a nearly featureless plane — the 30x exaggeration is what makes the rift valley and transform faults read as relief at all.

In [ ]:

deep_blues = LinearSegmentedColormap.from_list(
    'deep_blues', colormaps['Blues_r'](np.linspace(0.0, 0.82, 256))
)

source.plot(
    cmap=deep_blues,
    color=ColorScaling.power(gamma=0.7),
    colorbar=ColorBar(label='elevation (m relative to sea level)'),
    data_style=DataStyle(
        hillshade={
            'azimuth': 315,
            'altitude': 45,
            'vert_exag': 30.0,
            'dx': 460,
            'dy': 460,
            'blend_mode': 'soft',
        }
    ),
    title='GEBCO 2020 shaded relief — Mid-Atlantic Ridge (Azores)',
)

deep_blues = LinearSegmentedColormap.from_list( 'deep_blues', colormaps['Blues_r'](np.linspace(0.0, 0.82, 256)) ) source.plot( cmap=deep_blues, color=ColorScaling.power(gamma=0.7), colorbar=ColorBar(label='elevation (m relative to sea level)'), data_style=DataStyle( hillshade={ 'azimuth': 315, 'altitude': 45, 'vert_exag': 30.0, 'dx': 460, 'dy': 460, 'blend_mode': 'soft', } ), title='GEBCO 2020 shaded relief — Mid-Atlantic Ridge (Azores)', )