this page tries to summarise the use of GeoData classes in marble so that its implementation details can match the use cases, and understand if any what issues might arise from manipulating them otherwise.
The use cases identified so far are:
- use any GeoData class as a convenient data holder in APIs.
- It is expected in that regard that classes have shared data.
- Let's call this usecase the "ToolClass" usecase.
- use GeoDataDocument as the root document of a "data file" in-memory representation, or even another grouping of information.
- In this use case, there would exist a "tree" of data matching a logical grouping of information.
- Let's call this usecase the "DataTree" usecase.
Actual Implemented Use Details
- GeoData classes have shared data, in the sense that e.g. copying a GeoDataFeature is a shallow copy, with deep copy happening when one of the instances need to modify a value.
- Reading a file with GeoParser creates a tree of data.
This data is manipulated within a stack of GeoNodes and internally stored in QVector of value types like QVector<GeoDataFeature>
- PlaceMarkManager creates its copy of any placemark in opened files
- Model classes (implementing Qt's model-view framework that is) serve as interface to GeoData classes, passing them through QVariants
Common Issues and Pitfalls
In the past or present, some issues have appeared and need to be remembered/adressed:
- memory ownership is an issue to be determined depending on use case.
- Compliance with KML spec is a priority, limiting differing needs.
- Parsing code is full of casts.
- storing e.g. an GeoDataPlacemark item in a QVector<GeoDataFeature> looks like a hairy solution, as QVector<T>::append will internally create a new T. In the shared data context this implies that we end up with an element of vector being a GeoDataFeature with a private member being a GeoDataPlacemarkPrivate.