quickstart_filters.md

Appendix D.1. NetCDF-4 Filter QuickStart {#nc_filters_quickstart}
==============================

> For full **Filters** documentation, see \ref filters.

**The `libnetcdf.so` library cannot talk to plugin libraries directly. Instead, it requires an "interface" library, which acts as a go-between.  The interface libraries are built by the netCDF libraries, when the underlying plugin libraries are detected during configure/build.**

Building and Installing the Interface Libraries {#nc_filters_qs_building}
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### Configuring 

When configuring netcdf via either the `configure` script or via `cmake`, you'll need to specify the location to install the interface libraries, as follows:

* configure: `--enable-plugins` `--with-plugin-dir=$NCPLUGIN_DIR`
* cmake: `-DPLUGIN_INSTALL_DIR=$NCPLUGIN_DIR`

where `$NCPLUGIN_DIR` is the path to the user-defined directory, e.g. `/usr/local/nc-plugins`

After compiling and installing `libnetcdf`, the interface libraries for those filters detected will be installed in the user-specified `NCPLUGIN_DIR`.

> `nc-config --plugindir` will return the location where plugins were installed. 

Using the Interface Libraries at Run-time {#nc_filters_qs_runtime}
---------------------------------

For historical reasons, `libnetcdf` uses the environmental variable `HDF5_PLUGIN_PATH` to locate the interface libraries at run-time. This location should be set to the `$NCPLUGIN_DIR` specified when building and installing `libnetcdf`.


Example Workflow (blosc) {#nc_filters_qs_workflow_example}
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From scratch, the steps to get this to work are as follows, and assumes `libhdf5` was installed.

1. Install the filter library, and the associate development headers.
2. Configure netCDF with `--enable-plugins` and `--with-plugin-dir=$HOME/netcdf-plugins`
3. Ensure `blosc` is specified in the generated `libnetcdf.settings` file.  
4. Run make, make install.

Once built and installed, set the environmental variable `HDF5_PLUGIN_PATH=$HOME/netcdf-plugins`.  

The reason this works is because:

1. NetCDF builds the interface library.
2. `ncdump` knows where to find the interface library because `HDF5_PLUGIN_PATH` is set.