CFFI

The CFFI Layer is the innermost wrapper in PyMEOS architecture, and it is generated by the CFFI Library.
It is located inside the pymeos_cffi package, and the files used to build it are the following:

• builder/meos.h
  C header file that is going to be wrapped by CFFI. It is a slightly modified version of the meos.h file provided by the MEOS Library, and contains some extra type/functions definitions needed in PyMEOS that are defined in liblwgeom.h or other parts of MEOS.
• builder/build_header.py
  Generates the modified meos.h header file mention right above. It takes the header file provided by the MEOS Library and adds the extra definitions needed.
• builder/build_helpers.py
  Contains the additional definitions needed for the C Header file
• builder/build_pymeos.py
  Reads the modified C Header file and wraps it with using the CFFI library to create a C Extension Module that can be imported from python.

Update

If the MEOS library has an API update (e.g. addition, modification or deletion of a function/type), the custom header file has to be updated before generating the wrapper. To do so, run the build_header.py script from the pymeos_cffi directory:

foo@bar:~/PyMEOS/pymeos_cffi$ python3 ./pymeos_cffi/builder/build_header.py <path-to-header-file>

For easier copying:

python3 ./pymeos_cffi/builder/build_header.py <path-to-header-file>

If the path to the header file it's not provided, it defaults to /usr/local/include/meos.h

Generation

Before building the extension module, make sure these extra header files are available in the same location as the meos.h header file provided by MEOS:

• postgis_revision.h
• postgis_config.h
• lwinline.h
• liblwgeom.h (an include has to be modified from #include "../postgis_config.h" to #include "postgis_config.h"

These file are available in the MEOS source code after running CMake.
To do this easily, you can run the following script:

copy_headers() {
  p="$1"
  sudo cp "$p/postgis/postgis_revision.h" /usr/local/include/
  sudo cp "$p/postgis/postgis_config.h" /usr/local/include/
  sudo cp "$p/postgis/liblwgeom/lwinline.h" /usr/local/include/
  sudo cp "$p/postgis/liblwgeom/liblwgeom.h" /usr/local/include/
  sudo sed -i 's/\.\.\/postgis/postgis/' /usr/local/include/liblwgeom.h
}
copy_headers <path-to-meos-source-code>

To test that the wrapper generation works properly before going on with the next wrapper layer (CFFI Wrapper), you can generate with it by running the build_pymeos.py script from the pymeos_cffi directory:

foo@bar:~/PyMEOS/pymeos_cffi$ python3 ./pymeos_cffi/builder/build_pymeos.py

For easier copying:

python3 ./pymeos_cffi/builder/build_pymeos.py

If it was successful, three files should have been generated in the current folder:

• _meos_cffi.c: Containing all the C code generated by CFFI
• _meos_cffi.o: Resulting from the compilation of the previous file
• _meos_cffi.**.(so|dll|dylib): Shared library that can be loaded in python to call MEOS functions (the name and extension will vary depending on the system)