Plotting shaded relief#

Hyoga colormaps#

In addition to the vast selection of matplotlib built-in colormaps, hyoga add three custom colormaps for altitude maps (Topographic, Bathymetric, and Elevational) and two half-transparent colormaps for relief-shading (Glossy, and Matte).

These new colormaps are registered with matplotlib after importing hyoga, which means that they can be used in any matplotlib plot method:

import numpy as np

x = y = np.linspace(-3, 3, 256)
x, y = np.meshgrid(x, y)
z = (1 - x/2 + x**5 + y**3) * np.exp(-x**2 - y**2)
plt.contourf(x, y, z, cmap='Elevational', levels=12)

In addition, these colormaps trigger special behaviour when used in some of hyoga’s plot methods. Here is an example plotting bedrock altitude contours for the example data using the Topographic colormap.

with hyoga.open.example('pism.alps.in.boot.nc') as ds:
    ds.hyoga.plot.bedrock_altitude_contours(cmap='Topographic', vmin=0)
    ds.hyoga.plot.bedrock_hillshade(cmap='Glossy')

Note how the bedrock altitude contour levels are not equidistant, but are instead densified at lower elevation to highlight lower reliefs and fit the highly skewed Topographic colormap.

Shaded relief#

Relief shading can be used to add depth to maps. In hyoga, hillshading is implemented using a slightly differently mechanics than that provided by matplotlib.colors.LightSource. While matplotlib “blends” hillshades into topograhic maps, hyoga plots hillshades as a new image independent of underlying topography. This is what a simple hillshade image looks like:

with hyoga.open.example('pism.alps.vis.refined.nc') as ds:
    ds.hyoga.plot.bedrock_hillshade()

While Dataset.hyoga.plot.bedrock_hillshade() uses the bedrock altitude, an equivalent Dataset.hyoga.plot.surface_hillshade() plots shaded relief from the ice surface altitude. By default, however, hillshades are plotted as a half-transparent layer best overlaid onto an altitude map:

with hyoga.open.example('pism.alps.vis.refined.nc') as ds:
    ds.hyoga.plot.bedrock_altitude(cmap='Topographic')
    ds.hyoga.plot.bedrock_hillshade()

The illumination direction can be customized using altitude and azimuth angles. Low relief can be accentuated using an exag exaggeration factor:

with hyoga.open.example('pism.alps.vis.refined.nc') as ds:
    ds.hyoga.plot.bedrock_altitude(cmap='Topographic')
    ds.hyoga.plot.bedrock_hillshade(altitude=30, azimuth=-15, exag=3)

The altitude and azimuth arguments accepts lists, allowing multidirectional shaded relief. The weight arguments applies different weight to different light sources. The default uses triple illumination from the northwest. Here is a more advanced example using six weighted light sources from all directions.

with hyoga.open.example('pism.alps.vis.refined.nc') as ds:
    ds.hyoga.plot.bedrock_altitude(cmap='Topographic')
    ds.hyoga.plot.bedrock_hillshade(
        altitude=45, azimuth=[15, 75, 135, 195, 255, 315],
        weight=[0.2, 0.125, 0.1, 0.125, 0.2, 0.25])

Plotting shaded relief

Page contents

Plotting shaded relief#

Hyoga colormaps#

Shaded relief#