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94 lines
3.7 KiB
Markdown
94 lines
3.7 KiB
Markdown
# QtPBFImagePlugin
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Qt image plugin for displaying Mapbox vector tiles
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## Description
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QtPBFImagePlugin is a Qt image plugin that enables applications capable of
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displaying raster MBTiles maps or raster XYZ online maps to also display
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PBF(MVT) vector tiles without (almost, see usage) any application modifications.
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Standard Mapbox GL Styles are used for styling the maps. Most relevant style
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features used by [Maputnik](http://editor.openmaptiles.org) are supported.
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The style is loaded from the
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[$AppDataLocation](http://doc.qt.io/qt-5/qstandardpaths.html)/style/style.json
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file on plugin load. If the style uses a sprite, the sprite JSON file must
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be named sprite.json and the sprite image sprite.png and both files must be
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placed in the same directory as the style itself. A default fallback style
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(OSM-Liberty) for OpenMapTiles is part of the plugin.
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"Plain" PBF files as well as gzip compressed files (as used in MBTiles) are
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supported by the plugin.
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## Usage
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Due to a major design flaw in the Mapbox vector tiles specification - the zoom
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is not part of the PBF data - the plugin can not be used "as is", but passing
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the zoom level is necessary. This is done by exploiting the optional *format*
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parameter of the QImage constructor or the QImage::fromData() or
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QPixmap::loadFromData() functions. The zoom number is passed as ASCII string
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to the functions:
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```cpp
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QPixmap pm;
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pm.loadFromData(tileData, QString::number(zoom).toLatin1());
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```
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The plugin supports vector scaling using QImageReader's setScaledSize() method,
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so when used like in the following example:
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```cpp
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QImageReader reader(file, QString::number(zoom).toLatin1());
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reader.setScaledSize(QSize(512, 512));
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reader.read(&image);
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```
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you will get 512x512px tiles with a pixel ratio of 2 (= HiDPI tiles).
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## Build
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### Requirements
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* Qt >= 5.4 (5.6 for HiDPI support)
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* Google Protocol Buffers (protobuf-lite)
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* Zlib
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### Build steps
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#### Linux
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```shell
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qmake pbfplugin.pro
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make
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```
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#### Windows
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```shell
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qmake PROTOBUF=path/to/protobuf ZLIB=path/to/zlib pbfplugin.pro
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nmake
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```
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#### OS X
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```shell
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qmake PROTOBUF=path/to/protobuf pbfplugin.pro
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make
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```
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## Install
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Copy the plugin to the system Qt image plugins path to make it work. You may
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also set the QT_PLUGIN_PATH system variable before starting the application. For
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Linux, there are RPM and DEB [packages](https://build.opensuse.org/project/show/home:tumic:QtPBFImagePlugin)
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for most common distros available on OBS.
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## Limitations
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* Only data that is part of the PBF file is displayed. External layers defined in the
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style are ignored.
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* Text PBF features must have a unique id (OpenMapTiles >= v3.7) for the text layout
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algorithm to work properly.
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## Status
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A picture is worth a thousand words. Data and styles from https://openmaptiles.org.
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#### OSM-liberty
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#### Klokantech-basic
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## Applications using QtPBFImagePlugin
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* [GPXSee](https://www.gpxsee.org)
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