Catalog - 52North/IlwisCore GitHub Wiki

A Catalog is a representation of something that acts as a container for other ILWIS Objects. The most obvious example is a folder on disk, but also diverse things like hdf files (raster file), WFS services or zip files may act as Catalog. It is important to realize that a Catalog always gives access to the whole set of contained objects and not to a filtered subset. Objects in a Catalog can be accessed through the URL identification mechanism that ILWIS uses to locate data sources. The URL of the container is then appended with the name of the source to be accessed.

It is important to realize that a data source can appear in multiple roles (types) in a Catalog. For example, take a GeoTiff file. The obvious type of such file is a RasterCoverage. However, the GeoTiff file also contains information about its spatial reference. So a GeoTiff can also be represented (and used!) as CoordinateSystem. A Catalog will contain a reference to a RasterCoverage, CoordinateSystem (and Domain, and GeoReference) for the same data source. That is why the combination location/type is unique and not location only.

All objects that ILWIS 'sees' are administered in the MasterCatalog. ILWIS scans folders, queries remote sources through its CatalogConnector to discover which data sources can be found at the location. The sources it can recognize are stored as Resource in the MasterCatalog. Each connector has its own way of doing this (a file is different from a WMS layer but they end up as Resource in the MasterCatalog).

The MasterCatalog is stored as a database and thus can be queried as such.