Popularity
7.1
Stable
Activity
6.5
-
817
21
96

Description

Package orb defines a set of types for working with 2d geo and planar/projected geometric data in Golang. There are a set of sub-packages that use these types to do interesting things. They each provider their own README with extra info.

Programming language: Go
License: MIT License
Tags: GIS     Geospatial     WKB     Geo     Geojson     Wkt     Mapbox-vector-lite     2d    
Latest version: v0.5.0

orb alternatives and similar packages

Based on the "GIS" category.
Alternatively, view orb alternatives based on common mentions on social networks and blogs.

Do you think we are missing an alternative of orb or a related project?

Add another 'GIS' Package

README

orb CI codecov Go Report Card Go Reference

Package orb defines a set of types for working with 2d geo and planar/projected geometric data in Golang. There are a set of sub-packages that use these types to do interesting things. They each provider their own README with extra info.

Interesting features

  • Simple types - allow for natural operations using the make, append, len, [s:e] builtins.
  • GeoJSON - support as part of the [geojson](geojson) sub-package.
  • Mapbox Vector Tile - encoding and decoding as part of the [encoding/mvt](encoding/mvt) sub-package.
  • Direct to type from DB query results - by scanning WKB data directly into types.
  • Rich set of sub-packages - including [clipping](clip), [simplifing](simplify), [quadtree](quadtree) and more.

Type definitions

type Point [2]float64
type MultiPoint []Point

type LineString []Point
type MultiLineString []LineString

type Ring LineString
type Polygon []Ring
type MultiPolygon []Polygon

type Collection []Geometry

type Bound struct { Min, Max Point }

Defining the types as slices allows them to be accessed in an idiomatic way using Go's built-in functions such at make, append, len and with slice notation like [s:e]. For example:

ls := make(orb.LineString, 0, 100)
ls = append(ls, orb.Point{1, 1})
point := ls[0]

Shared Geometry interface

All of the base types implement the orb.Geometry interface defined as:

type Geometry interface {
    GeoJSONType() string
    Dimensions() int // e.g. 0d, 1d, 2d
    Bound() Bound
}

This interface is accepted by functions in the sub-packages which then act on the base types correctly. For example:

l := clip.Geometry(bound, geom)

will use the appropriate clipping algorithm depending on if the input is 1d or 2d, e.g. a orb.LineString or a orb.Polygon.

Only a few methods are defined directly on these type, for example Clone, Equal, GeoJSONType. Other operation that depend on geo vs. planar contexts are defined in the respective sub-package. For example:

  • Computing the geo distance between two point:

    p1 := orb.Point{-72.796408, -45.407131}
    p2 := orb.Point{-72.688541, -45.384987}
    
    geo.Distance(p1, p2)
    
  • Compute the planar area and centroid of a polygon:

    poly := orb.Polygon{...}
    centroid, area := planar.CentroidArea(poly)
    

GeoJSON

The [geojson](geojson) sub-package implements Marshalling and Unmarshalling of GeoJSON data. Features are defined as:

type Feature struct {
    ID         interface{}  `json:"id,omitempty"`
    Type       string       `json:"type"`
    Geometry   orb.Geometry `json:"geometry"`
    Properties Properties   `json:"properties"`
}

Defining the geometry as an orb.Geometry interface along with sub-package functions accepting geometries allows them to work together to create easy to follow code. For example, clipping all the geometries in a collection:

fc, err := geojson.UnmarshalFeatureCollection(data)
for _, f := range fc {
    f.Geometry = clip.Geometry(bound, f.Geometry)
}

The library supports third party "encoding/json" replacements such github.com/json-iterator/go. See the [geojson](geojson) readme for more details.

Mapbox Vector Tiles

The [encoding/mvt](encoding/mvt) sub-package implements Marshalling and Unmarshalling MVT data. This package uses sets of geojson.FeatureCollection to define the layers, keyed by the layer name. For example:

collections := map[string]*geojson.FeatureCollection{}

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

// In order to be used as source for MapboxGL geometries need to be clipped
// to max allowed extent. (uncomment next line)
// layers.Clip(mvt.MapboxGLDefaultExtentBound)

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

// Depending on use-case remove empty geometry, those too small to be
// represented in this tile space.
// In this case lines shorter than 1, and areas smaller than 2.
layers.RemoveEmpty(1.0, 2.0)

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

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

Decoding WKB from a database query

Geometries are usually returned from databases in WKB format. The [encoding/wkb](encoding/wkb) sub-package offers helpers to "scan" the data into the base types directly. For example:

row := db.QueryRow("SELECT ST_AsBinary(point_column) FROM postgis_table")

var p orb.Point
err := row.Scan(wkb.Scanner(&p))

db.Exec("INSERT INTO table (point_column) VALUES (ST_GeomFromWKB(?))", wkb.Value(p))

Scanning directly from MySQL columns is supported. By default MySQL returns geometry data as WKB but prefixed with a 4 byte SRID. To support this, if the data is not valid WKB, the code will strip the first 4 bytes, the SRID, and try again. This works for most use cases.

List of sub-package utilities

  • [clip](clip) - clipping geometry to a bounding box
  • [encoding/mvt](encoding/mvt) - encoded and decoding from Mapbox Vector Tiles
  • [encoding/wkb](encoding/wkb) - well-known binary as well as helpers to decode from the database queries
  • [encoding/wkt](encoding/wkt) - well-known text encoding
  • [geojson](geojson) - working with geojson and the types in this package
  • [maptile](maptile) - working with mercator map tiles and quadkeys
  • [project](project) - project geometries between geo and planar contexts
  • [quadtree](quadtree) - quadtree implementation using the types in this package
  • [resample](resample) - resample points in a line string geometry
  • [simplify](simplify) - linear geometry simplifications like Douglas-Peucker