Configuration

Satpy has two levels of configuration that allow to control how Satpy and its various components behave. There are a series of “settings” that change the global Satpy behavior. There are also a series of “component configuration” YAML files for controlling the complex functionality in readers, compositors, writers, and other Satpy components that can’t be controlled with traditional keyword arguments.

Settings

There are configuration parameters in Satpy that are not specific to one component and control more global behavior of Satpy. These parameters can be set in one of three ways:

  1. Environment variable

  2. YAML file

  3. At runtime with satpy.config

This functionality is provided by the donfig library. The currently available settings are described below. Each option is available from all three methods. If specified as an environment variable or specified in the YAML file on disk, it must be set before Satpy is imported.

YAML Configuration

YAML files that include these parameters can be in any of the following locations:

  1. <python environment prefix>/etc/satpy/satpy.yaml

  2. <user_config_dir>/satpy.yaml (see below)

  3. ~/.satpy/satpy.yaml

  4. <SATPY_CONFIG_PATH>/satpy.yaml (see Component Configuration Path below)

The above user_config_dir is provided by the appdirs package and differs by operating system. Typical user config directories are:

  • Mac OSX: ~/Library/Preferences/satpy

  • Unix/Linux: ~/.config/satpy

  • Windows: C:\\Users\\<username>\\AppData\\Local\\pytroll\\satpy

All YAML files found from the above paths will be merged into one configuration object (accessed via satpy.config). The YAML contents should be a simple mapping of configuration key to its value. For example:

cache_dir: "/tmp"
data_dir: "/tmp"

Lastly, it is possible to specify an additional config path to the above options by setting the environment variable SATPY_CONFIG. The file specified with this environment variable will be added last after all of the above paths have been merged together.

At runtime

After import, the values can be customized at runtime by doing:

import satpy
satpy.config.set(cache_dir="/my/new/cache/path")
# ... normal satpy code ...

Or for specific blocks of code:

import satpy
with satpy.config.set(cache_dir="/my/new/cache/path"):
    # ... some satpy code ...
# ... code using the original cache_dir

Similarly, if you need to access one of the values you can use the satpy.config.get method.

Cache Directory

  • Environment variable: SATPY_CACHE_DIR

  • YAML/Config Key: cache_dir

  • Default: See below

Directory where any files cached by Satpy will be stored. This directory is not necessarily cleared out by Satpy, but is rarely used without explicitly being enabled by the user. This defaults to a different path depending on your operating system following the appdirs “user cache dir”.

Cache Longitudes and Latitudes

  • Environment variable: SATPY_CACHE_LONLATS

  • YAML/Config Key: cache_lonlats

  • Default: False

Whether or not generated longitude and latitude coordinates should be cached to on-disk zarr arrays. Currently this only works in very specific cases. Mainly the lon/lats that are generated when computing sensor and solar zenith and azimuth angles used in various modifiers and compositors. This caching is only done for AreaDefinition-based geolocation, not SwathDefinition. Arrays are stored in cache_dir (see above).

When setting this as an environment variable, this should be set with the string equivalent of the Python boolean values ="True" or ="False".

See also cache_sensor_angles below.

Warning

This caching does not limit the number of entries nor does it expire old entries. It is up to the user to manage the contents of the cache directory.

Cache Sensor Angles

  • Environment variable: SATPY_CACHE_SENSOR_ANGLES

  • YAML/Config Key: cache_sensor_angles

  • Default: False

Whether or not generated sensor azimuth and sensor zenith angles should be cached to on-disk zarr arrays. These angles are primarily used in certain modifiers and compositors. This caching is only done for AreaDefinition-based geolocation, not SwathDefinition. Arrays are stored in cache_dir (see above).

This caching requires producing an estimate of the angles to avoid needing to generate new angles for every new data case. This happens because the angle generation depends on the observation time of the data and the position of the satellite (longitude, latitude, altitude). The angles are estimated by using a constant observation time for all cases (maximum ~1e-10 error) and by rounding satellite position coordinates to the nearest tenth of a degree for longitude and latitude and nearest tenth meter (maximum ~0.058 error). Note these estimations are only done if caching is enabled (this parameter is True).

When setting this as an environment variable, this should be set with the string equivalent of the Python boolean values ="True" or ="False".

See also cache_lonlats above.

Warning

This caching does not limit the number of entries nor does it expire old entries. It is up to the user to manage the contents of the cache directory.

Component Configuration Path

  • Environment variable: SATPY_CONFIG_PATH

  • YAML/Config Key: config_path

  • Default: []

Base directory, or directories, where Satpy component YAML configuration files are stored. Satpy expects configuration files for specific component types to be in appropriate subdirectories (ex. readers, writers, etc), but these subdirectories should not be included in the config_path. For example, if you have custom composites configured in /my/config/dir/etc/composites/visir.yaml, then config_path should include /my/config/dir/etc for Satpy to find this configuration file when searching for composites. This option replaces the legacy PPP_CONFIG_DIR environment variable.

Note that this value must be a list. In Python, this could be set by doing:

satpy.config.set(config_path=['/path/custom1', '/path/custom2'])

If setting an environment variable then it must be a colon-separated (:) string on Linux/OSX or semicolon-separate (;) separated string and must be set before calling/importing Satpy. If the environment variable is a single path it will be converted to a list when Satpy is imported.

export SATPY_CONFIG_PATH="/path/custom1:/path/custom2"

On Windows, with paths on the C: drive, these paths would be:

set SATPY_CONFIG_PATH="C:/path/custom1;C:/path/custom2"

Satpy will always include the builtin configuration files that it is distributed with regardless of this setting. When a component supports merging of configuration files, they are merged in reverse order. This means “base” configuration paths should be at the end of the list and custom/user paths should be at the beginning of the list.

Data Directory

  • Environment variable: SATPY_DATA_DIR

  • YAML/Config Key: data_dir

  • Default: See below

Directory where any data Satpy needs to perform certain operations will be stored. This replaces the legacy SATPY_ANCPATH environment variable. This defaults to a different path depending on your operating system following the appdirs “user data dir”.

Demo Data Directory

  • Environment variable: SATPY_DEMO_DATA_DIR

  • YAML/Config Key: demo_data_dir

  • Default: <current working directory>

Directory where demo data functions will download data files to. Available demo data functions can be found in satpy.demo subpackage.

Download Auxiliary Data

  • Environment variable: SATPY_DOWNLOAD_AUX

  • YAML/Config Key: download_aux

  • Default: True

Whether to allow downloading of auxiliary files for certain Satpy operations. See Auxiliary Data Download for more information. If True then Satpy will download and cache any necessary data files to Data Directory when needed. If False then pre-downloaded files will be used, but any other files will not be downloaded or checked for validity.

Sensor Angles Position Preference

  • Environment variable: SATPY_SENSOR_ANGLES_POSITION_PREFERENCE

  • YAML/Config Key: sensor_angles_position_preference

  • Default: “actual”

Control which satellite position should be preferred when generating sensor azimuth and sensor zenith angles. This value is passed directly to the get_satpos() function. See the documentation for that function for more information on how the value will be used. This is used as part of the get_angles() and get_satellite_zenith_angle() functions which is used by multiple modifiers and composites including the default rayleigh correction.

Component Configuration

Much of the functionality of Satpy comes from the various components it uses, like readers, writers, compositors, and enhancements. These components are configured for reuse from YAML files stored inside Satpy or in custom user configuration files. Custom directories can be provided by specifying the config_path setting mentioned above.

To create and use your own custom component configuration you should:

  1. Create a directory to store your new custom YAML configuration files. The files for each component will go in a subdirectory specific to that component (ex. composites, enhancements, readers, writers).

  2. Set the Satpy config_path to point to your new directory. This could be done by setting the environment variable SATPY_CONFIG_PATH to your custom directory (don’t include the component sub-directory) or one of the other methods for setting this path.

  3. Create YAML configuration files with your custom YAML files. In most cases there is no need to copy configuration from the builtin Satpy files as these will be merged with your custom files.

  4. If your custom configuration uses custom Python code, this code must be importable by Python. This means your code must either be installed in your Python environment or you must set your PYTHONPATH to the location of the modules.

  5. Run your Satpy code and access your custom components like any of the builtin components.