Qt image plugin for displaying Mapbox vector tiles

QtPBFImagePlugin is a Qt image plugin that enables applications capable of displaying raster MBTiles maps or raster XYZ online maps to also display PBF(MVT) vector tiles without (almost, see usage) any application modifications.

Standard Mapbox GL Styles are used for styling the maps. Most relevant style features used by Maputnik are supported. A set of default styles for the OpenMapTiles, Mapbox, Protomaps and Versatiles tile shemes is part of the plugin.

The default tile size is 512px.

Due to a major design flaw in the Mapbox vector tiles specification - the zoom is not part of the PBF data - the plugin can not be used "as is", but passing the zoom level is necessary. This is done by exploiting the optional format parameter of the QImage constructor or the QImage::loadFromData() or QPixmap::loadFromData() functions. The zoom number is passed as ASCII string to the functions:

QImage img;
img.loadFromData(data, QByteArray::number(zoom));

For a complete code sample see the pbf2png conversion utility.

The plugin supports vector scaling using the QImageReader::setScaledSize() method, so when used like in the following example:

QImage img;
QImageReader reader(file, QByteArray::number(zoom));
reader.setScaledSize(QSize(1024, 1024));
reader.read(&img);

you will get 1024x1024px tiles with a pixel ratio of 2 (= HiDPI tiles). The maximal tile size is 4096x4096px.

Since version 3 of the plugin tile overzoom is supported. If you set format to $zoom;$overzoom:

QImage img;
QByteArray fmt(QByteArray::number(zoom) + ';' + QByteArray::number(overzoom));
img.loadFromData(data, fmt);

you will get (512<<overzoom)x(512<<overzoom)px tiles with a pixel ratio of 1. When overzoom is combined with setScaledSize(), the base size is the overzoomed tile size.

Since version 5 of the plugin style selection is supported. If you set format to $zoom;$overzoom;$style:

QImage img;
QByteArray fmt(QByteArray::number(zoom) + ';' + QByteArray::number(overzoom) \
  + ';' + QByteArray::number(style));
img.loadFromData(data, fmt);

the style-th style available will be used to render the tile.

To retrieve a list of available styles, call QImageReader::text() with the "Description" key:

QImageReader reader(&imageData);
QString info(reader.text("Description"));

This will fill info with a JSON array like:

[
  {
    "layers": [
      "aerodrome_label",
      "aeroway",
      "boundary",
      "building",
      "landcover",
      "landuse",
      "park",
      "place",
      "poi",
      "transportation",
      "transportation_name",
      "water",
      "water_name",
      "waterway"
    ],
    "name": "OpenMapTiles"
  },
  {
    "layers": [
      "boundaries",
      "buildings",
      "earth",
      "landcover",
      "landuse",
      "places",
      "pois",
      "roads",
      "water"
    ],
    "name": "Protomaps"
  }
]

The map styles are loaded from subdirectories of the $AppDataLocation/style directory on plugin load, one style per subdirectory. If the style uses a sprite, the sprite JSON file must be named sprite.json and the sprite image sprite.png and both files must be placed in the same directory as the style itself.

For a set of compatible styles for various different tile schemes see the QtPBFImagePlugin-styles repository.

• Qt5 >= 5.15 or Qt6 (Android builds require Qt6)

qmake pbfplugin.pro
make

qmake pbfplugin.pro
nmake

Copy the plugin to the system Qt image plugins path to make it work. You may also set the QT_PLUGIN_PATH system variable before starting the application. For Linux, there are RPM and DEB packages for most common distros available on OBS.

• Only data that is part of the PBF file is displayed. External layers defined in the style are ignored.
• Text PBF features must have a unique id (OpenMapTiles >= v3.7) for the text layout algorithm to work properly. Additionally, the tile buffer must be large enough to contain all neighboring text features overlapping to the tile bounds (only data from the tile itself can be drawn to the resulting image).
• Expressions are not supported in the styles, only the original GL zoom functions are implemented.

Changelog

A picture is worth a thousand words.

• Data: MapTiler
• Style: OSM-liberty

• Data: Mapbox
• Style: Bright

• Data: HERE
• Style: Apollo-Bright

• GPXSee