PyMGL: Maplibre GL Native Static Renderer for Python

This package provides an interface to Mapblibre Native to render Mapbox GL / Maplibre GL styles to PNG images.

WARNING: this package is under active development and the API may change without notice.

Goals

This package is intended to provide a lightweight interface to maplibre-native for rendering Mapbox GL / Maplibre GL styles to PNG image data using Python. This is particularly useful for server-side rendering of maps for use in reports.

This package provides only the Python API for interacting with maplibre-native; it does not provide higher-level functionality such as a web server or a CLI.

Install

Supported operating systems

MacOS 12+, Ubuntu 18+, Debian 10+, Fedora 29+, RHEL 8+, Alma Linux 8+

x86_64 and arm64 wheels are available on PyPI:

pip install pymgl

NOTE: x86_64 wheels are not currently available for MacOS.

To verify that pymgl installed correctly, install with the test dependencies and run the included test suite:

pip install pymgl[test]
pytest --pyargs pymgl -v

Windows

Windows is not and will not be supported.

Usage

To create a map object, you must always provide a Mapbox GL / Maplibre GL style JSON string or URL to a well-known style hosted by Mapbox or Maptiler:

from pymgl import Map

style = """{
    "version": 8,
    "sources": {
        "basemap": {
            "type": "raster",
            "tiles": ["https://services.arcgisonline.com/arcgis/rest/services/Ocean/World_Ocean_Base/MapServer/tile/{z}/{y}/{x}"],
            "tileSize": 256
        }
    },
    "layers": [
        { "id": "basemap", "source": "basemap", "type": "raster" }
    ]
}"""

map = Map(style, <height=256>, <width=256>, <ratio=1>, <longitude=0>, <latitude=0>, <zoom=0>, <token=None>, <provider=None>)

See the styles section for more information about map styles.

Other than style, all other parameters are optional with default values.

NOTE: style and ratio cannot be changed once the instance is constructed.

You can use a well-known style instead of providing a style JSON string, but you must also provide a token and identify the correct provider:

map = Map("mapbox://styles/mapbox/streets-v11", token=<mapbox token>, provider="mapbox")

Valid providers are mapbox, maptiler, and maplibre.

Map properties

You can set additional properties on the map instance after it is created:

map.setCenter(longitude, latitude)

map.setZoom(zoom)

map.setSize(width, height)

map.setBearing(bearing)  # map bearing in degrees

map.setPitch(pitch)  # map pitch in degrees

map.setFilter(layerId, filterJSON or None)

map.setPaintProperty(layerId, property, value)

map.setVisibility(layerId, True / False)

You can retrieve these values using attributes, if needed:

map.size  # (width, height)

map.center  # (longitude, latitude)

map.zoom

map.bearing

map.pitch

You can also retrive information about the map's style or a specific layer:

map.listLayers()  # [<layerId1>, ...]

map.listSources()  # [<sourceId1>, ...]

map.getFilter(<layerId>)  # returns JSON value or None

map.getPaintProperty(<layerId>, <property>)  # returns JSON value or None

map.getLayerJSON(<layerId>)  # returns JSON describing layer

NOTE: paint properties may be decoded to their internal representation. For example, a CSS color string #FF0000 will be returned as ["rgba", 255, 0, 0, 1].

IMPORTANT: if you are using a remotely-hosted style, you need to force the map to load - which loads all underying assets - before listing the style's layers, sources, or other properties.

map = Map("mapbox://styles/mapbox/streets-v11", token=<mapbox token>, provider="mapbox")

map.listLayers()  # []
map.load()
map.listLayers()  # [<layerId1>, ...]

Alternatively, you can download the style yourself and provide that as input to the Map, and it will show all layers without requiring a render first. However, not all assets will be loaded until the first render.

from urllib.request import urlopen

url = f"https://api.mapbox.com/styles/v1/mapbox/streets-v11?access_token={MAPBOX_TOKEN}"

with urlopen(url) as r:
    style = r.read()

map = Map(style.decode("UTF-8") token=<mapbox token>, provider="mapbox")
map.listLayers()  # [<layerId1>, ...]

You can auto-fit the map to bounds instead of using center longitude / lantitude and zoom:

map.setBounds(xmin, ymin, xmax, ymax, <padding=0>)

You can register an image for use with your style by providing an ID, raw image bytes, width, height, pixel ratio, and indicate if it should be interpreted as SDF:

map.addImage("id", img_bytes, width, height, <ratio=1>, <make_SDF=False>)

See the SDF image docs for more information about using SDF images.

Rendering

You can render the map to PNG bytes:

img_bytes = map.renderPNG()

This returns bytes containing the RGBA PNG data.

You can render the map to a raw buffer as a numpy array (uint8 dtype):

array = map.renderBuffer()

The array is a sequence of RGBA values for each pixel in the image.

This may be useful if you are going to immediately read the image data into another package such as Pillow or pyvips to combine with other image operations.

Map instances

WARNING: you must manually delete the map instance if you assign a new map instance to that variable, or this package will segfault (not yet sure why). This problem does not occur if separate instances are assigned to separate variables.

map = Map(<style>, <width>, <height>)

del map  # must manually delete BEFORE creating a new instance assigned to this

map = Map(<style>, <width>, <height>)

For this reason, you should consider using a context manager:

with Map(<style>, <width>, <height>) as map:
    map.renderPNG()

You can also use the map instance to directly render to PNG, if you don't need to set other properties on the map instance:

Map(<style>, <width>, <height>).renderPNG()

Styles

PyMGL should support basic styles as of Mapbox GL JS 1.13.

Remote tilesets, sources, and assets

Remote tilesets, tile sources, and assets (glyphs, sprites) should be well-supported. These are loaded by the underlying C++ library outside our control. Invalid URLs will generally raise errors. However, network timeouts or incorrect formats may cause the process to crash.

Local mbtiles

Local MBTiles are supported, but must be provided using an absolute path to the mbtiles file as the source url of a tileset; it must resolve to an actual file.

Local MBTiles are denoted with a mbtiles:// URI prefix.

Example:

{
    "sources": {
        "source_id": {
            "url": "mbtiles:///<pymgl_root_dir>/tests/fixtures/geography-class-png.mbtiles",
            ...
        }
    },
    "layers": [...],
    ...
}

Local files

GeoJSON files and other local file assets are supported, but must be provided using an absolute path to the file source.

Example:

{
    "sources": {
        "geojson": {
            "type": "geojson",
            "data": "file:///<pymgl_root_dir>/tests/fixtures/test.geojson"
        }
    },
    "layers": [...],
    ...
}

WARNING: providing a URI to tiles under the tiles key of a source is NOT currently supported by Maplibre Native; attempting to do so will fail.

Images

You must register the image with the map instance before rendering the map. See map.addImage() above.

{
    "sources": {...},
    "layers": [
        {
            ...,
            "paint": {
                "fill-pattern": "pattern"
            }
        },
    ]
}

You can use map images as fill patterns or icon images.

Adding sources and layers after construction

You can add sources and layers dynamically after constructing the map instance:

import json

map = Map("")  # construct with empty style

map.addSource("my_id", json.dumps({
    "type": "geojson",
    "data": {"type": "Point", "coordinates": [0, 0]}
}))

map.addLayer(json.dumps({
    "id": "geojson-point",
    "source": "geojson",
    "type": "circle",
    "paint": { ... }
}))

Feature state

You can get, set, and remove feature state after the map has been loaded.

map = Map(<style with source "exampleSource" and layer "exampleLayer">, ...)

map.load()
map.getFeatureState("exampleSource", "exampleLayer", "0")  # returns None
map.setFeatureState("exampleSource", "exampleLayer", "0", "{\"a\": true}")
map.getFeatureState("exampleSource", "exampleLayer", "0")  # returns "{\"a\": true}"

# remove the state value for key "a"
map.removeFeatureState("exampleSource", "exampleLayer", "0", "a")
map.render()
map.getFeatureState("exampleSource", "exampleLayer", "0")  # returns None

NOTE: features must already have a unique, numeric ID set on each feature. There is currently no support for promoteId like in MapLibre GL JS.

IMPORTANT: the map must be loaded before getting or setting feature state. You must manually force a render in order for the map to update feature state after removing a state key

Unsupported features

PyMGL does not support alternative projections or 3D terrain.

Developing

Dependencies:

MacOS:

Developing on MacOS requires the following binary libraries to be installed via homebrew:

• cmake
• ninja

Developing on Ubuntu requires the following binary libraries:

• cmake
• ninja-build
• build-essential
• libcurl4-openssl-dev
• libicu-dev
• libpng-dev
• libwebp-dev
• libprotobuf-dev
• libjpeg-turbo8-dev
• libx11-dev
• libegl-dev
• libopengl-dev
• xvfb

To run on Linux, XVFB must also be running; otherwise the process will segfault.

See docker/README.md for more information.

nanobind

nanonbind is used to provide bindings for Python against a C++ class that wraps maplibre-native for easier rendering operations.

It is included here as a git submodule, per the installation instructions.

git submodule add https://github.com/wjakob/nanobind vendor/nanobind
cd vendor/nanobind
git submodule update --init --recursive

Then to upgrade to a specific version of nanobind for development, if needed:

cd vendor/nanobind
git checkout <version tag>

Maplibre Native

Maplibre Native is included as a git submodule, and it includes many submodules of its own.

git submodule add -b main https://github.com/maplibre/maplibre-native vendor/maplibre-native

Git submodules

Run

git submodule update --init

We only need some of the submodules under maplibre-native. In particular, we do not need maplibre-gl-js or Android / IOS dependencies.

Run the following:

cd vendor/maplibre-native

git submodule update --init --recursive \
    vendor/boost \
    vendor/cpp-httplib \
    vendor/earcut.hpp \
    vendor/eternal \
    vendor/googletest \
    vendor/metal-cpp \
    vendor/polylabel \
    vendor/protozero \
    vendor/mapbox-base \
    vendor/unique_resource \
    vendor/unordered_dense \
    vendor/vector-tile \
    vendor/wagyu \
    vendor/zip-archive

To later update maplibre-native:

cd vendor/maplibre-native
git checkout main
git pull origin

cd ../..
git commit -am "update maplibre-native" to latest

Architecture

This package is composed of 2 main parts:

• wrapper around Maplibre Native classes to make constructing and managing properties of the map easier
• Python bindings created using nanobind against that wrapper

The wrapper is located in src/map.cpp.

Build

C++ tests

See tests/README for more information.

Build Python extension

The Python setup.py script manages building the library and extension using CMake.

From project root directory:

python setup.py build_ext --inplace

Docstrings / type information

Docstrings are maintained in both src/_pymgl.cpp and pymgl/__init__.pyi.

Python-friendly type annotations are maintained in pymgl/__init__.pyi.

Note: pymgl/__init__.pyi is necessary to support autocompletion and tooltips in VSCode.

Building wheels

Most wheels are automatically built by Github when pushing a new version tag. Linux Arm64 wheels must be built locally on an Arm64 machine (e.g., MacOS host).

These are created using the manylinux_2_28 Docker container.

docker build -f ci/Dockerfile.manylinux_2_28_aarch64 -t pymgl-manylinux_2_28_aarch64 .
docker run -v "$PWD/:/app" pymgl-manylinux_2_28_aarch64 ci/build_linux_wheels.sh

This will create aarch64 wheels in dist that can be uploaded directly to PyPI.

See also

mbgl-renderer provides a NodeJS API, CLI, and server based on the NodeJS bindings to Mapbox GL Native.

Credits

This project was developed with the support of the U.S. Fish and Wildlife Service Southeast Conservation Adaptation Strategy for use in the Southeast Conservation Blueprint Viewer.

This project is made possible because of the mapbox-gl-native project by Mapbox by the efforts of the Maplibre community maintaining the open-source fork of that project at maplibre-native.