Distribution Statement
# # # This source code is subject to the license referenced at
# # # NRLMMD-GEOIPS.

Colormaps in GeoIPS#

A colormap is a module-based GeoIPS plugin that works in conjunction with an image-based output formatter to dictate which colors are used to represent your data. GeoIPS colormaps are structured as Python dictionaries that contain the information needed for the output formatter to apply a colormap to the final image. This information can include things like the matplotlib-compatible colormap (existing or user-created), the data range covered by the colormap, and information about the colorbar (if one is desired).

Most colormappers include a standard set of information that is useful for plotting:

  • cmap: The matplotlib colormap object that will be applied to the image.

  • norm: An object that scales your values so the colorbar covers the specified range.

  • colorbar: A boolean indicating whether to include a colorbar in the image.

  • cbar_ticks: Data points at which to place tick marks.

  • cbar_tick_labels: labels for the tick marks (a list of strings; should be the same length as cbar_ticks).

  • cbar_label: The label of the colorbar.

  • boundaries: A matplotlib parameter that is used to specify the boundaries within the colormap.

  • cbar_spacing: A matplotlib parameter that determines if each color has the same size in the colorbar, or if it is based on the proportion of data it covers.

  • cbar_full_width: A boolean indicating whether the colorbar should cover the full width of the image.

Other keyword arguments can be passed to the matplotlib colorbar in some output formatters using the colorbar_kwargs, set_ticks_kwargs, and set_label_kwargs keys.

For an example of how a custom colormapper is formatted, see the Infrared colormapper.

Using a Colormapper#

Colormappers can be applied in two ways:

1. Inclusion in Product Specifications: If using one of the existing output formatters in GeoIPS, the colormapper can be included in the product default specification, which can be executed via the command line or a test script using a GeoIPS procflow.

For examples of including a colormapper in a product implementation, see the Extend GeoIPS with a Colormapper and product defaults tutorials.

2. Direct Invocation: If you have your own output formatter, the colormapper can be called directly:

from geoips.interfaces import colormappers
cmap_name = "Infrared"
mpl_colors_info = colormappers.get_plugin(cmap_name)

The output of the plugin can then be applied to the plot of the image. For example:

from geoips.image_utils.mpl_utils import create_colorbar

main_ax.imshow(
    data,
    transform=mapobj,
    extent=mapobj.bounds,
    cmap=mpl_colors_info["cmap"],  # Use the colormap defined in the colormapper
    norm=mpl_colors_info["norm"],  # with the defined norm.
    **extra_args,
)

if mpl_colors_info["colorbar"] is True:
    # Create the colorbar defined in the colormapper.
    create_colorbar(fig, mpl_colors_info)
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