Users settings are passed to CARACal through a configuration file consisting of a sequence of blocks — each corresponding to the run of a CARACal worker. The workers are run following the order in which they appear in the configuration file. For reference see List and Brief description of CARACal workers.
Within each worker’s block of the configuration file, the worker’s parameters are arranged in a nested structure following the YAML syntax rules (see https://yaml.readthedocs.io). As an example, a block of the config file may look like:
worker_name: enable: true parameter_1: value_1 parameter_2: parameter_2_1: value_2_1 parameter_2_2: value_2_2 parameter_3: value_3 ...
The complete list of all workers’ parameters is available at Workers parameters, where the parameters’ nesting is also illustrated.
Workers can be executed more than once in a single run of CARACal. This could be useful, for example, if a user wants to flag the data both before and after cross-calibration. To indicate a new run of a worker the worker name must be followed by “__<suffix>” in the configuration file (note the double underscore). The first run of a worker can also have a “__<suffix>” but does not have to. In the example above, the flag worker must thus appear twice in the configuration file:
flag__beforecrosscal: enable: true parameter_1: value_1A ... [other workers] flag__aftercrosscal: enable: true parameter_1: value_1B ...
Most parameters are optional and do not need to be included in the configuration file. Their default values are set to work in as many cases as possible. A few parameters are compulsory. The pages at Workers parameters indicate whether a parameter is optional, its data type, allowed values (if applicable) and default value.
CARACal comes with a set of sample configuration files. These are available at https://github.com/caracal-pipeline/caracal/tree/master/caracal/sample_configurations and include, for example:
- minimalConfig.yml, which includes as few parameters as possible and performs a basic data reduction including both continuum and spectral line imaging;
- meerkat-continuum-defaults.yml, which is optimised for the reduction of data taken with the MeerKAT telescope for the purpose of total-intensity continuum imaging.
Users could take these sample configuration files as a starting point for their work.