Getting started¶

Although largely automated, OGGM model still requires some python scripting to prepare and run a simulation. This section will guide you through several examples to get you started.

Important

Did you know that you can try OGGM in your browser before installing it on your computer? Visit Try OGGM online for more information.

First step: system settings for input data¶

OGGM needs various input data files to run. Currently, we rely exclusively on open-access data that are all downloaded automatically for the user. OGGM implements a bunch of tools to make access to input data as painless as possible for you, including the automated download of all the required files. This requires you to tell OGGM where to store these data. Let’s start by opening a python interpreter and type:

In [1]: from oggm import cfg

In [2]: cfg.initialize()


At your very first import, this will do two things:

1. It will download a small subset of data used for testing and calibration. Those data are located in your home directory, in a hidden folder called .oggm.
2. It will create a configuration file in your home folder, where you can indicate where you want to store further input data. This configuration file is also located in your home directory under the name .oggm_config.

To locate this config file, you can type:

In [3]: cfg.CONFIG_FILE
Out[3]: '/home/docs/.oggm_config'


Important

The default settings will probably work for you, but we recommend to have a look at this file and set the paths to a directory where enough space is available: a minimum of 8 Gb for all climate data and glacier outlines is necessary. Pre-processed glacier directories can quickly grow to several tens of Gb as well, even for regional runs.

At the first import, OGGM will create a cached .oggm directory in your $HOME folder. This directory contains all data obtained from the oggm sample data repository. It contains several files needed only for testing, but also some important files needed for calibration and validation (e.g. the reference mass-balance data from WGMS with links to the respective RGI polygons). The ~/.oggm directory should be updated automatically when you update OGGM, but if you encounter any problems with it, simply delete the directory (it will be re-downloaded automatically at the next import). All other data: auto-downloads and the ~/.oggm_config file¶ Unlike runtime parameters (such as physical constants or working directories), input data are shared across runs and even across computers if you want to. Therefore, the paths to previously downloaded data are stored in a configuration file that you’ll find in your $HOME folder: the ~/.oggm_config file.

The file should look like:

dl_cache_dir = /path/to/download_cache
tmp_dir = /path/to/tmp_dir
rgi_dir = /path/to/rgi_dir
test_dir = /path/to/test_dir
has_internet = True


Some explanations:

• dl_cache_dir is a path to a directory where all the files you downloaded will be cached for later use. Most of the users won’t need to explore this folder (it is organized as a list of urls) but you have to make sure to set this path to a folder with sufficient disk space available. This folder can be shared across compute nodes if needed (it is even recommended for HPC setups). Once a file is stored in this cache folder (e.g. a specific DEM tile), OGGM won’t download it again.
• dl_cache_readonly indicates if writing is allowed in this folder (this is the default). Setting this to True will prevent any further download in this directory (useful for cluster environments, where this data might be available on a readonly folder): in this case, OGGM will use a fall back directory in your current working directory.
• tmp_dir is a path to OGGM’s temporary directory. Most of the files used by OGGM are downloaded and cached in a compressed format (zip, bz, gz…). These files are extracted in tmp_dir before use. OGGM will never allow more than 100 .tif (or 100 .nc) files to exist in this directory by deleting the oldest ones following the rule of the Least Recently Used (LRU) item. Nevertheless, this directory might still grow to quite a large size. Simply delete it if you want to get this space back.
• rgi_dir is the location where the RGI shapefiles are extracted.
• test_dir is the location where OGGM will write some of its output during tests. It can be set to tmp_dir if you want to, but it can also be another directory (for example a fast SSD disk). This folder shouldn’t take too much disk space but here again, don’t hesitate to delete it if you need to.

Note

For advanced users or cluster configuration: the user’s tmp_dir and rgi_dir settings can be overridden and set to a specific directory by defining an environment variable OGGM_EXTRACT_DIR to a directory path. Similarly, the environment variables OGGM_DOWNLOAD_CACHE and OGGM_DOWNLOAD_CACHE_RO override the dl_cache_dir and dl_cache_readonly settings.

OGGM workflow¶

For a step by step tutorial of the entire OGGM workflow, download the getting started jupyter notebook (right-click -> “Save link as”) and run it using the following command (from the directory where you downloaded the tutorial):

\$ jupyter-notebook getting_started.ipynb