Remove scikit-image as dependency

README.rst

@@ -52,15 +52,13 @@ Other optional packages include:
 * opencv-python_ (for the Lucas-Kanade optical flow)
 * pillow_ (for importing gif data)
 * pyproj_ (for cartographic transformations)
-* scikit-image_ (for the VET optical flow method)
 
 .. _basemap: https://matplotlib.org/basemap/
 .. _cartopy: https://scitools.org.uk/cartopy/docs/v0.16/
 .. _h5py: https://www.h5py.org/
 .. _opencv-python: https://opencv.org/
 .. _pillow: https://python-pillow.org/
 .. _pyproj: https://jswhit.github.io/pyproj/
-.. _scikit-image: https://scikit-image.org/
 
 We recommend that you create a conda environment using the available
 `environment.yml`_ file to install the most important dependencies::
@@ -76,6 +74,14 @@ This will allow running most of the basic functionalities in pysteps.
 Install from source
 -------------------
 
+**IMPORTANT**: installing from sources requires numpy to be installed
+beforehand.
+
+The installer need numpy to compile the Cython extensions.
+If numpy is not installed you can running in a terminal::
+
+    pip install numpy
+
 The lastest pysteps version in the repository can be installed using pip by
 simply running in a terminal::
 
@@ -99,6 +105,29 @@ If you want to install the package in a specific directory run::
     python setup.py install --prefix=/path/to/local/dir
 
 
+Non anaconda users or minimal anaconda environments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The installation using **setup.py** will try to to install the minimum
+dependencies needed to run the program correctly.
+If you are not using the suggested conda environment (defined in
+environment.yml) or you are working with a minimal python distribution,
+you may get the following error during the installation::
+
+    ModuleNotFoundError: No module named 'Cython'
+
+This means that Cython is not installed, which is needed to build some of the
+dependencies of pysteps.
+
+For non anaconda users, you can install Cython using::
+
+    pip install Cython
+
+Anaconda users can install Cython using::
+
+    conda install cython
+
+
 Setting up the user-defined configuration file
 ----------------------------------------------
 

environment.yml

@@ -14,4 +14,3 @@ dependencies:
   - pillow
   - pyproj
   - scipy
-  - scikit-image