Improve and simplify Mercator layers management #847
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Inheritance of displayName and pickEnabled reviewed.
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Description of the Changes
Refactor MercatorTiledImageLayer to include all general initialization, such as: sector, zero level delta, display name, image size, detectBlankImages and mapSizeForLevel calculation into parent constructor. This makes child layers avoiding unnecessary copy-paste code.
Added first level offset parameter which allows to skip several top levels to avoid displaying one tile over whole globe.
Added alternative way of determining tile URL by overriding getImageSourceUrl function. This allows to create additional online layers by setting several parameters in constructor and overriding one function with URL builder instead of separate URL builder creation.
Why Should This Be In Core?
This feature simplify adding new typical online layers such as Google, OSM, OTM. Wiki, etc by only specifying core parameters without unnecessary copy-paste of the same logic.
This approach already implemented in Java and will be implemented in Android.
Benefits
Simple Mercator online sources creation.
Potential Drawbacks
Less flexibility of constructor.