package mvt

orb – github.com/paulmach/orb/encoding/mvt Index | Examples | Files | Directories

import "github.com/paulmach/orb/encoding/mvt"

Index ¶

Constants
Variables
func Marshal(layers Layers) ([]byte, error)
func MarshalGzipped(layers Layers) ([]byte, error)
type Layer

func NewLayer(name string, fc *geojson.FeatureCollection) *Layer
func (l *Layer) Clip(box orb.Bound)
func (l *Layer) ProjectToTile(tile maptile.Tile)
func (l *Layer) ProjectToWGS84(tile maptile.Tile)
func (l *Layer) RemoveEmpty(lineLimit, areaLimit float64)
func (l *Layer) Simplify(s orb.Simplifier)

type Layers

func NewLayers(layers map[string]*geojson.FeatureCollection) Layers
func Unmarshal(data []byte) (Layers, error)
func UnmarshalGzipped(data []byte) (Layers, error)
func (ls Layers) Clip(box orb.Bound)
func (ls Layers) ProjectToTile(tile maptile.Tile)
func (ls Layers) ProjectToWGS84(tile maptile.Tile)
func (ls Layers) RemoveEmpty(lineLimit, areaLimit float64)
func (ls Layers) Simplify(s orb.Simplifier)
func (ls Layers) ToFeatureCollections() map[string]*geojson.FeatureCollection

Examples ¶

Marshal

Constants ¶

const (
	// DefaultExtent for mapbox vector tiles. (https://www.mapbox.com/vector-tiles/specification/)
	DefaultExtent = 4096
)

Variables ¶

var ErrDataIsGZipped = errors.New("failed to unmarshal, data possibly gzipped")

var (
	// MapboxGLDefaultExtentBound holds the default mapbox vector tile bounds used by mapbox-gl.
	// (https://www.mapbox.com/mapbox-gl-js/style-spec/#sources-vector)
	MapboxGLDefaultExtentBound = orb.Bound{
		Min: orb.Point{-1 * DefaultExtent, -1 * DefaultExtent},
		Max: orb.Point{2*DefaultExtent - 1, 2*DefaultExtent - 1},
	}
)

Functions ¶

func Marshal ¶

func Marshal(layers Layers) ([]byte, error)

Marshal will take a set of layers and encode them into a Mapbox Vector Tile format. Features that have a nil geometry, for some reason, will be skipped and not included.

Example¶

Code:play

package main

import (
	"log"

	"github.com/paulmach/orb/encoding/mvt"
	"github.com/paulmach/orb/geojson"
	"github.com/paulmach/orb/maptile"
	"github.com/paulmach/orb/simplify"
)

func main() {
	// Start with a set of feature collections defining each layer in lon/lat (WGS84).
	collections := map[string]*geojson.FeatureCollection{}

	// Convert to a layers object and project to tile coordinates.
	layers := mvt.NewLayers(collections)
	layers.ProjectToTile(maptile.New(17896, 24449, 16)) // x, y, z

	// Simplify the geometry now that it's in the tile coordinate space.
	layers.Simplify(simplify.DouglasPeucker(1.0))

	// Depending on use-case remove empty geometry, those two small to be
	// represented in this tile space.
	// In this case lines shorter than 1, and areas smaller than 1.
	layers.RemoveEmpty(1.0, 1.0)

	// encoding using the Mapbox Vector Tile protobuf encoding.
	data, err := mvt.Marshal(layers) // this data is NOT gzipped.
	_ = data

	// error checking
	if err != nil {
		log.Fatalf("marshal error: %v", err)
	}

	// Sometimes MVT data is stored and transferred gzip compressed. In that case:
	data, err = mvt.MarshalGzipped(layers)
	_ = data

	// error checking
	if err != nil {
		log.Fatalf("marshal error: %v", err)
	}
}

func MarshalGzipped ¶

func MarshalGzipped(layers Layers) ([]byte, error)

MarshalGzipped will marshal the layers into Mapbox Vector Tile format and gzip the result. A lot of times MVT data is gzipped at rest, e.g. in a mbtiles file.

Types ¶

type Layer ¶

type Layer struct {
	Name     string
	Version  uint32
	Extent   uint32
	Features []*geojson.Feature
}

Layer is intermediate MVT layer to be encoded/decoded or projected.

func NewLayer ¶

func NewLayer(name string, fc *geojson.FeatureCollection) *Layer

NewLayer is a helper to create a Layer from a feature collection and a name, it sets the default extent and version to 1.

func (*Layer) Clip ¶

func (l *Layer) Clip(box orb.Bound)

Clip will clip all geometries in this layer to the given bounds. Will remove features that clip to an empty geometry, modifies the layer.Features slice in place.

func (*Layer) ProjectToTile ¶

func (l *Layer) ProjectToTile(tile maptile.Tile)

ProjectToTile will project all the geometries in the layer to tile coordinates based on the extent and the mercator projection.

func (*Layer) ProjectToWGS84 ¶

func (l *Layer) ProjectToWGS84(tile maptile.Tile)

ProjectToWGS84 will project all the geometries backed to WGS84 from the extent and mercator projection.

func (*Layer) RemoveEmpty ¶

func (l *Layer) RemoveEmpty(lineLimit, areaLimit float64)

RemoveEmpty will remove line strings shorter/smaller than the limits.

func (*Layer) Simplify ¶

func (l *Layer) Simplify(s orb.Simplifier)

Simplify will run the layer geometries through the simplifier.

type Layers ¶

type Layers []*Layer

Layers is a set of layers.

func NewLayers ¶

func NewLayers(layers map[string]*geojson.FeatureCollection) Layers

NewLayers creates a set of layers given a set of feature collections.

func Unmarshal ¶

func Unmarshal(data []byte) (Layers, error)

Unmarshal takes Mapbox Vector Tile (MVT) data and converts into a set of layers, It does not project the coordinates.

func UnmarshalGzipped ¶

func UnmarshalGzipped(data []byte) (Layers, error)

UnmarshalGzipped takes gzipped Mapbox Vector Tile (MVT) data and unzips it before decoding it into a set of layers, It does not project the coordinates.

func (Layers) Clip ¶

func (ls Layers) Clip(box orb.Bound)

Clip will clip all geometries in all layers to the given bounds.

func (Layers) ProjectToTile ¶

func (ls Layers) ProjectToTile(tile maptile.Tile)

ProjectToTile will project all the geometries in all layers to tile coordinates based on the extent and the mercator projection.

func (Layers) ProjectToWGS84 ¶

func (ls Layers) ProjectToWGS84(tile maptile.Tile)

ProjectToWGS84 will project all the geometries in all the layers backed to WGS84 from the extent and mercator projection.

func (Layers) RemoveEmpty ¶

func (ls Layers) RemoveEmpty(lineLimit, areaLimit float64)