Marble uses Qt's Model/View framework as a way to signal updates to a model to interested parts. In that respect, a Model class can wrap any possible data.
The multiple models in Marble each fit the purpose of feeding some GeoData classes to interested widgets. The way those models are fed could be improved however:
The solution to this is twofold:
This solution however is not a one size fit all, because an interested class with some knowledge of the GeoDataTypes for example would be far better off manipulating the methods of GeoData classes.
As a consequence, a choice should be made whether to access GeoData through the model-view framework (nice for a List Widget or for a generic presentation of 'data as a tree', really not so nice for a class which for example would like to calculate the bounding box of all geometric data of a GeoDataDocument, or even for the File read/write, as the knowledge of data types is really known).
There are multiple models with various levels of implementation. Some are needed, others should die...
Here is the list of Model class, and a description of how they are used.
It represents a data file, parsed into a GeoDataDocument tree structure.
It is used by the DataViewPlugin debug plugin (and is broken atm)
It represents a list of gpx data file represented as GpxFile
This was originally intended to but used as the model for the File List View ( which is accessible by running marble with --enableFileView ) but has since been replaced by the FileViewModel.
The model that is in the GpsLayer is currently only being used as a collection class and is deprecated. This, along with the whole current GPX implementation, needs to be removed and updated to the current concepts in Marble. See Gpx Status
It is used by the GeoRenderPlugin to access the list of vector data to draw it.
It is used by no other code.
It represents the list of all Placemarks of all opened kml files. the PlaceMarkManager appends all the placemarks after reading a file.