A high performance library for working with vector tiles from the team at MapBox.
Provides C++ headers that support rendering geodata into vector tiles and rendering vector tiles into images.
Many efforts at vector tiles use GeoJSON or other text based formats that are easy to parse in the browser.
This approach is different: tiles are encoded as protobuf messages and storage is tightly designed around the Mapnik rendering engine. In this case Mapnik is the client rather than the browser. This provides a geodata format that is a drop-in replacement for datasources like postgis and shapefiles without compromising on speed and can be styled using existing design tools like TileMill.
Vector tiles in this code represent a direct serialization of Mapnik layers
optimized for space efficient storage and fast deserialization directly back
into Mapnik objects. For those familiar with the Mapnik API vector tiles
here can be considered a named array of mapnik::featureset_ptr whose geometries
have been pre-tiled.
A vector tile can consist of one or more ordered layers identified by name and containing one or more features.
Features contain attributes and geometries: either point, linestring, or polygon. Features expect single geometries so multipolygons or multilinestrings are represented as multiple features, each storing a single geometry part.
Geometries are stored as an x,y,command stream (where command is a rendering command
like move_to or line_to). Geometries are clipped, reprojected into the map srs,
converted to screen coordinates, and delta
and zigzag encoded.
Feature attributes are encoded as key:value pairs which are dictionary encoded at the layer level for compact storage of any repeated keys or values. Values use variant type encoding supporting both unicode strings, boolean values, and various integer and floating point types.
Vector tiles are serialized as protobuf messages which are then zlib compressed.
The assumed projection is Spherical Mercator (epsg:3857).
- Mapnik v2.2.0:
libmapnikandmapnik-config - Protobuf:
libprotobufandprotoc
apt-get install libprotobuf7 libprotobuf-dev protobuf-compiler
apt-add-repository ppa:mapnik/v2.2.0
apt-get update && apt-get install libmapnik libmapnik-dev
brew install protobuf
brew install mapnik
Just type:
make
This builds the protobuf C++ wrappers: vector_tile.pb.cc and vector_tile.pb.h
Then include vector_tile.pb.cc in your code. The rest is header only.
Run the C++ tests like:
make test
See examples in examples/c++
These require the protobuf python bindings and the rtree library
which can be installed like:
sudo apt-get install libspatialindex-dev
pip install protobuf rtree
To build and test the python example code do:
make python && make python-test
Run the example code:
python examples/python/hello-world.py