Frequently Asked Questions

Is your library mature for production code?

Not really. The API is not always as clever as I wish it would, and it will probably change in the future. Salem is well tested though, at least for the cases I encounter in my daily work.

What others tools should I know about?

The python atmospheric sciences community is a bit spread between iris and xarray for N-Dimensional data handling. I find that xarray is very intuitive to learn thanks to its strong interaction with pandas.

Here are some tools that share functionalities with Salem:

• cartopy is the reference tool for plotting on maps. Salem provides a way to plot with cartopy in addition to Salem’s homegrowm graphics. (see Graphics)
• Salem provides useful reprojection tools (see Map transformations). The transformation routines are quite fast (we use pyproj for the map transformations and scipy for the interpolation) but they are all done on memory (i.e. not adapted for large datasets). For large reprojection workflows you might want to have a look at cartopy and pyresample.
• regionmask provides similar tools as salem’s region-of-interest functionalities if you are woking with shapefiles. regionmask seems a bit more general than Salem, but I’m not sure if it works with any map projection as Salem does.
• In the future, I hope that pangeo-data will overtake most of the functionalities I need. But this is not going to happen tomorrow...

Several libraries are available to meteorologists and climatologists, but I don’t think they share much functionality with Salem: for example MetPy, windspharm, xgcm, aospy, and all the ones I forgot to mention.

Why developing Salem?

As an atmospheric scientist, I hate to have to take care about projections and maps. Salem was created to hide all these concerns. By the time I started, it seemed a good idea to provide map transformation tools without depending on GDAL (thanks to conda-forge GDAL is now much easier to install). It is still possible to do reprojection work in Salem using scipy and pyproj alone.

Furthermore, I use the atmospheric model WRF quite often in my work. Its output files are absolutely not compliant with the CF conventions. To my knowledge, there is no tool to plot and manipulate WRF data with Python, and Salem will be further developed with this model in mind.

What’s this ”.salem_cache” directory in my home folder?

At the first import, Salem will create a hidden directory called .salem_cache in your home folder. It will be used to download Salem’s demo files and standard shapefiles. This directory is also used by joblib to store the result of slow operations such as reading and transforming shapefiles, or downloading google maps from the internet. The cache should not become too large, but if it does: simply delete it.