No test data for NGA extensions

[bradh]

There are NGA defined extensions that are documented, but the is no representative data that allows testing, or shows the intended use.

[bosborn]

Created a rivers GeoPackage demonstrating both extensions. Added example links to the GeoPackage in the extensions at http://ngageoint.github.io/GeoPackage/docs/extensions/

It would be useful if geopackage.org had examples linked for each gpkg extension.

[bradh]

Thanks - appreciated.