README
¶
MVT
This package contains functions and types for encoding a geometry in Mapbox Vector Tiles. This package depends on the protbuf package.
In short, a Tiles has Layers, which have Feautures. The Feature type
is what holds a single geom.Geometry and associated metadata.
To encode a geometry into a tile, you need:
- a geometry
- a tile's
geom.Extentin the same projection as the geometry - the size of the tile you want to output in pixels
note: the geometry must not go outside the tile extent. If this is unknown, use the clip package before encoding.
To encode:
- Call
PrepareGeomtry, it returns ageom.Geometrythat is "reprojected" into pixel values relative to the tile - Add the returned geometry to a
Feature, optionally with an ID and tags by callingNewFeatures. - Add the feature to a
Layerwith a name for the layer by calling(*Layer).AddFeatures - Add the layer to a
Tileby calling(*Tile).AddLayers - Get the
protobuftile by calling(*Tile).VTile - Encode the
protobufinto bytes withproto.Marshal
For an example, check the use of this package in tegola/atlas/map.go
Documentation
¶
Overview ¶
Package mvt is used to encode MVT tiles
In short, a `Tile`s has `Layer`s, which have `Feauture`s. The `Feature` type is what holds a single `geom.Geometry` and associated metadata.
To encode a geometry into a tile, you need:
- a geometry
- a tile's `geom.Extent` in the same projection as the geometry
- the size of the tile you want to output in pixels
note: the geometry must not go outside the tile extent. If this is unknown, use the clip package before encoding. (https://godoc.org/github.com/go-spatial/geom/planar/clip#Geometry)
To encode:
- Call `PrepareGeomtry`, it returns a `geom.Geometry` that is "reprojected" into pixel values relative to the tile
- Add the returned geometry to a `Feature`, optionally with an ID and tags by calling `NewFeatures`.
- Add the feature to a `Layer` with a name for the layer by calling `(*Layer).AddFeatures`
- Add the layer to a `Tile` by calling `(*Tile).AddLayers`
- Get the `protobuf` tile by calling `(*Tile).VTile`
- Encode the `protobuf` into bytes with `proto.Marshal`
For an example, check the use of this package in tegola/atlas/map.go (https://github.com/go-spatial/tegola/blob/master/atlas/map.go)
Index ¶
- Constants
- Variables
- func DecodeGeometry(gtype vectorTile.Tile_GeomType, b []uint32) (geom.Geometry, error)
- func NewCursor() *cursor
- func PrepareGeo(geo geom.Geometry, tile *geom.Extent, pixelExtent float64) geom.Geometry
- func TileGeomCollection(tile *Tile) geom.Collection
- type Command
- type Feature
- type Layer
- func (l *Layer) AddFeatures(features ...Feature)
- func (l *Layer) Extent() int
- func (l *Layer) Features() (f []Feature)
- func (l *Layer) RemoveFeature(idxs ...int)
- func (l *Layer) SetExtent(e int)
- func (l *Layer) VTileLayer(ctx context.Context) (*vectorTile.Tile_Layer, error)
- func (*Layer) Version() int
- type Tile
Constants ¶
const (
MimeType = "application/vnd.mapbox-vector-tile"
)
Variables ¶
var ( ErrNilFeature = fmt.Errorf("feature is nil") ErrUnknownGeometryType = fmt.Errorf("unknown geometry type") ErrNilGeometryType = fmt.Errorf("geometry is nil") )
var ( Version uint32 = 2 DefaultExtent uint32 = 4096 )
var ErrExtraData = errors.New("mvt: invalid extra data")
Functions ¶
func DecodeGeometry ¶
func DecodeGeometry(gtype vectorTile.Tile_GeomType, b []uint32) (geom.Geometry, error)
func PrepareGeo ¶
PrepareGeo converts the geometry's coordinates to tile pixel coordinates. tile should be the extent of the tile, in the same projection as geo. pixelExtent is the dimension of the (square) tile in pixels usually 4096, see DefaultExtent. This function treats the tile extent elements as left, top, right, bottom. This is fine when working with a north-positive projection such as lat/long (epsg:4326) and web mercator (epsg:3857), but a south-positive projection (ie. epsg:2054) or west-postive projection would then flip the geomtery. To properly render these coordinate systems, simply swap the X's or Y's in the tile extent.
func TileGeomCollection ¶
func TileGeomCollection(tile *Tile) geom.Collection
TileGeomCollection returns all geometries in a tile as a collection
Types ¶
type Command ¶
type Command uint32
func NewCommand ¶
NewCommand return a new command encoder
type Feature ¶
Feature describes a feature of a Layer. A layer will contain multiple features each of which has a geometry describing the interesting thing, and the metadata associated with it.
func NewFeatures ¶
NewFeatures returns one or more features for the given Geometry
func (*Feature) VTileFeature ¶
func (f *Feature) VTileFeature(ctx context.Context, keys []string, vals []interface{}) (tf *vectorTile.Tile_Feature, err error)
VTileFeature will return a vectorTile.Feature that would represent the Feature
type Layer ¶
type Layer struct {
// Name is the unique name of the layer within the tile
Name string
// contains filtered or unexported fields
}
Layer describes a layer within a tile. Each layer can have multiple features
func (*Layer) AddFeatures ¶
AddFeatures will add one or more Features to the Layer per the spec features SHOULD have unique ids but it's not required
func (*Layer) Features ¶
Features returns a copy of the features in the layer, use the index of the this array to remove any features from the layer
func (*Layer) RemoveFeature ¶
RemoveFeature allows you to remove one or more features, with the provided indexes. To figure out the indexes, use the indexs from the Features array.
func (*Layer) VTileLayer ¶
func (l *Layer) VTileLayer(ctx context.Context) (*vectorTile.Tile_Layer, error)
VTileLayer returns a vectorTile Tile_Layer object that represents this layer.
type Tile ¶
type Tile struct {
// contains filtered or unexported fields
}
Tile describes a Mapbox Vector Tile
func Decode ¶
Decode reads all the data from r and decodes the MVT tile into a Tile TODO(ear7h): handle tile tags
func DecodeByte ¶
DecodeByte decodes the MVT encoded bytes into a Tile. TODO(ear7h): handle tile tags
Source Files
¶
Directories
¶
| Path | Synopsis |
|---|---|
|
Package vectorTile is a generated protocol buffer package.
|
Package vectorTile is a generated protocol buffer package. |