Map

The map is by far the most complex widget. Let’s see how is works!

Map2D

First, let focus on the map itself, without all the elements that populates it.

The Map2D widget inherits QGraphicsView, and holds a MapScene (that inherits QGraphicsScene).

This widget only support maps in the Pseudo-Mercator projected coordinate system, a.k.a EPSG:3857. There are plans to support other coordinate systems in the future.

See https://www.maptiler.com/google-maps-coordinates-tile-bounds-projection/ to learn how this kind of map works.

In our case, the QGraphicsScene coordinates are directly related to the tiles coordinates, multiplied by the size of the tiles.

Example

• At zoom level 0, the map’s bottom right coordinate is (256, 256),

• At zoom level 1, it’s (512, 512),

• At zoom level 1, it’s (1024, 1024),

• …

See src/widgets/map/maputils.cpp for some helper functions.

There is a TileProvider, associated with each map layers. New tile providers can be added in the tile_sources.xml file.

Tiles are fist opened from local cache directory, or downloaded from the net is not present locally. Remove local cache to get the latest tiles.

Downloading tile can take a few seconds, or can fail. Before a tile is downloaded succesfully, it is recreated by assembling its 4 child tiles (at zoom n+1), or by scaling up its parent’s tile.