Add geoviews as extra optional dependency in setup.py

[weiji14]

List geoviews as an optional dependency in the setup.py file. Also set up travis to install PROJ and GEOS first so that cartopy (a requirement of geoviews) can be installed.

conda create -n icepyx-env -c conda-forge geos pip proj=7.2.0
conda activate icepyx-env
pip install -e .       # install required dependencies first 
pip install -e .[viz]  # install optional dependencies later

Note that PROJ version is pinned to 7.2.0 because PROJ 8.0.0 doesn't seem to be supported by cartopy yet, wait for SciTools/cartopy#1752.

Fixes #177.

References:

• https://setuptools.readthedocs.io/en/latest/userguide/dependency_management.html#optional-dependencies
• https://laszukdawid.com/2017/06/04/installing-cartopy-on-ubuntu-14-04-or-travis-ci/

[JessicaS11]

Thanks for putting this together, @weiji14! If @icetianli is unable to review, I will do so Friday.

[icetianli]

Thank you @weiji14 for this PR! I have been trying to install geoviews as extra dependency using the instructions in your comment:

conda create -n icepyx-env -c conda-forge pip proj=7.2.0
conda activate icepyx-env
pip install -e .[viz]

But it keeps showing the following errors about Fiona and Cartopy:

ERROR: Command errored out with exit status 1:
    Complete output (2 lines):
    Failed to get options via gdal-config: [Errno 2] No such file or directory: 'gdal-config'
    A GDAL API version must be specified. Provide a path to gdal-config using a GDAL_CONFIG environment variable or use a GDAL_VERSION environment variable.

fiona/_transform.cpp:606:10: fatal error: 'cpl_conv.h' file not found
  #include "cpl_conv.h"
           ^~~~~~~~~~~~
  1 error generated.
  error: command '/usr/bin/clang' failed with exit code 1
  ----------------------------------------
  ERROR: Failed building wheel for fiona
  Running setup.py clean for fiona
Failed to build cartopy fiona
ERROR: Could not build wheels for cartopy which use PEP 517 and cannot be installed directly

However, it works perfectly fine if I didn't add pip after conda-forge:

conda create -n icepyx-env -c conda-forge proj=7.2.0
conda activate icepyx-env
pip install -e .[viz]

Any idea why? Or is it just a typo...? Thanks!

[weiji14]

Hmm, you're right. This is why it is recommended to install geoviews/cartopy/shapely via conda because doing it via pip is a nightmare (see SciTools/cartopy#738 and SciTools/cartopy#805). But to explain things:

• The second one works because you're probably installing using the base environment's python/pip and it is picking up some dependencies installed elsewhere (not recommended though).
• The first one failed (I think) because geos needs to be installed too, and icepyx should try to install a minimum of cartopy 0.18.0 (instead of 0.17.0 which had some build issues). I've pushed commits 6fab434 and 6e0cdd4, so can you try the below and see if things work:

git checkout geoviews-dependency
conda create -n icepyx-env -c conda-forge geos pip proj=7.2.0
conda activate icepyx-env
pip install -e .
pip install -e .[viz]

Just to be clear, the geoviews install problem shouldn't matter to users who do conda install icepyx (as long as we list geoviews as a dependency in https://github.com/conda-forge/icepyx-feedstock/blob/master/recipe/meta.yaml). But users doing pip install icepyx[viz] might face issues of needing to install both PROJ and GEOS first.