1. Introduction for POD developers

This walkthrough contains information for developers wanting to contribute a process-oriented diagnostic (POD) module to the MDTF framework. There are two tracks through the material: one for developers who have an existing analysis script they want to adapt for use in the framework, and one for developers who are writing a POD from scratch.

Section 4 provides instructions for setting up POD development, in particular managing language and library dependencies through conda. For developers already familiar with version 2.0 of the framework, Section 2 summarizes changes from v2.0 to facilitate migration to v3.0. New developers can skip this section, as the rest of this walkthrough is self-contained.

Section 3 Provides a list of instructions for submitting a POD for inclusion in the framework. We require developers to submit PODs through GitHub. See Git-based development workflow for how to manage code through the GitHub website.

Section 5 provides overall guidelines for POD development. Section 6 is a reference for the POD’s settings file format. In Section 7, we walk the developers through the workflow of the framework, focusing on aspects that are relevant for the operation of individual PODs, and using the Example Diagnostic POD as a concrete example to illustrate how a POD works under the framework Section 8 provides coding best practices to address common issues encountered in submitted PODs..

1.1. Scope of a process-oriented diagnostic

The MDTF framework imposes requirements on the types of data your POD outputs and takes as input. In addition to the scientific scope of process-oriented diagnostics, the analysis that you intend to do needs to fit the following model:

Your POD should accept model data as input and express the results of its analysis in a series of figures, which are presented to the user in a web page. Input model data will be in the form of one NetCDF file (with accompanying dimension information) per variable, as requested in your POD’s settings file. Because your POD may be run on the output of any model, you should be careful about the assumptions your code makes about the layout of these files (eg, the range of longitude or the positive convention for vertical coordinates). Supporting data may be in any format and will not be modified by the framework (see next section).

The above data sources are your POD’s only input: your POD should not access the internet or other networked resources. You may provide options in the settings file for the user to configure when the POD is installed, but these cannot be changed each time the POD is run.

To achieve portability, the MDTF cannot accept PODs written in closed-source languages (eg, MATLAB or IDL). We also cannot accept PODs written in compiled languages (eg, C or Fortran): installation would rapidly become impractical if users had to check compilation options for each POD.

The output of your POD should be a series of figures in vector format (.eps or .ps). Optionally, we encourage POD developers to also save relevant output data (e.g., the output data being plotted) as netcdf files, to give users the ability to take the POD’s output and perform further analysis on it.

1.2. POD code organization and supporting data


In order to make your code run faster for the users, we request that you separate any calculations that don’t depend on the model data (e.g., pre-processing of observational data), and instead save the end result of these calculations in data files for your POD to read when it is run. We refer to this as “digested observational data,” but it refers to any quantities that are independent of the model being analyzed. For purposes of data provenance, reproducibility, and code maintenance, we request that you include all the pre-processing/data reduction scripts used to create the digested data in your POD’s code base, along with references to the sources of raw data these scripts take as input (yellow box in the figure).

Digested data should be in the form of numerical data, not figures, even if the only thing the POD does with the data is produce an unchanging reference plot. We encourage developers to separate their “number-crunching code” and plotting code in order to give end users the ability to customize output plots if needed. In order to keep the amount of supporting data needed by the framework manageable, we request that you limit the total amount of digested data you supply to no more than a few gigabytes.

In collaboration with PCMDI, a framework is being advanced that can help systematize the provenance of observational data used for POD development. This section will be updated when this data source is ready for public use.