Unified Metadata¶
The UnifiedMetadata object is the data access layer for users of this library. All of the other containers are pushed into the UnifiedMetadata object and this class acts as a giant lookup dictionary.
The UnifiedMetadata objet supports two key concepts: mappings and overrides.
Mappings¶
A mapping is a declaration that tells the UnifiedMetadata object where to get a specific piece of metadata. For example, support one had an IsisMetadata object and a GDALMetadata object as inputs. Both declare a bbox (bounding box). Which one should be used?
1imd = IsisMetadata('my_cube.cub')
2gd = GDALMetadata('my_tif.tif')
3
4umd = UnifiedMetadata([imd, gd])
If one runs the above example and attempts to access the bbox (umd.bbox), a warning will be returned because the bbox is ambiguous (i.e., it could come from two sources). A mapping can be used to tell the UnifiedMetadata object which source to use.
1imd = IsisMetadata('my_cube.cub')
2gd = GDALMetadata('my_tif.tif')
3
4mappings = {'bbox':IsisMetadata}
5umd = UnifiedMetadata([imd, gd], mappings=mappings)
Overrides¶
Overrides are used to either force a particular value to a given key or to explicitly define a value. Let’s look at an example:
1gd = GDALMetadata('my_tif.tif')
2
3overrides = {'href':'http://where_is_my_data/my_tif.tif'}
4
5umd = UnifiedMetadata([gd]
GDAL does not have any information about the ultimate, online location of your data. Both FGDC (<networkr>) and STAC (assets.self) would like the online location of the data provided. Since, the href is a missing key, one can use the overrides to provide that information.
Note
Alternatively, is it possible to write a single YAML file that contains the key:value pairs and pass that in as another data source. See YAML Metadata for an example.