geospatial

Documentation

Overview

Package geospatial implements objects and functions useful for representing a geographic State as a geospatial entity and performing operations on that entity such as: visualization with mapping tools and efficiently determining if a geographic coordinate is contained within the entity's borders

Index

• Constants
• type Coordinate
  • func LatLng(lat, lng float64) Coordinate
  • func (c Coordinate) MarshalJSON() ([]byte, error)
  • func (c Coordinate) String() string
  • func (c *Coordinate) UnmarshalJSON(data []byte) error
• type InvalidGeometryError
  • func (e *InvalidGeometryError) Error() string
• type Polygon
  • func NewPolygon(coords []Coordinate) (*Polygon, error)
  • func (p Polygon) Contains(coord Coordinate) (contains bool)
  • func (p Polygon) MarshalJSON() ([]byte, error)
  • func (p Polygon) String() string
  • func (p *Polygon) UnmarshalJSON(data []byte) error
  • func (p Polygon) Validate() error
• type RighthandRuleError
  • func (e *RighthandRuleError) Error() string
• type State
  • func NewState(name string, coords []Coordinate) (state State, err error)
  • func (s State) Contains(coordinate Coordinate) bool

Constants

const (
	RingTooShort         = "polygon ring too short, must contain at least 4 positions"
	RingUnclosed         = "polygon ring must be closed, first and last positions must be equal"
	RingCounterClockwise = "polygon exterior ring must be clockwise"
)

Types

type Coordinate

type Coordinate struct {
	Lng, Lat float64
}

Represents a single point on a map or spherical geometry

func LatLng

func LatLng(lat, lng float64) Coordinate

Creates the expected Coordinate object with ordered arguments by latitude and longitude

func (Coordinate) MarshalJSON

func (c Coordinate) MarshalJSON() ([]byte, error)

func (Coordinate) String

func (c Coordinate) String() string

Formats the coordinate as a string

func (*Coordinate) UnmarshalJSON

func (c *Coordinate) UnmarshalJSON(data []byte) error

type InvalidGeometryError

type InvalidGeometryError struct {
	// contains filtered or unexported fields
}

func (*InvalidGeometryError) Error

func (e *InvalidGeometryError) Error() string

type Polygon

type Polygon []Coordinate

Provides methods for validation and analysis of the geospatial shape represented by the array of coordinates

func NewPolygon

func NewPolygon(coords []Coordinate) (*Polygon, error)

Constructs a new instance of a Polygon struct with valid coordinates which satisfy the RFC 7946 GeoJSON specifications [See: 3.1.6 Polygon](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.6)

func (Polygon) Contains

func (p Polygon) Contains(coord Coordinate) (contains bool)

Uses the [Ray-casting algorithm] to efficiently identify if the given coordinate is contained within the geospatial polygon. In simple terms, this algorithm creates horizontal lines (rays) and counts the number of intersections with the polygon's boundaries, an odd number of intersections indicates that the coordinate lies within the boundaries of the polygon. [Ray-casting algortithm](https://rosettacode.org/wiki/Ray-casting_algorithm)

func (Polygon) MarshalJSON

func (p Polygon) MarshalJSON() ([]byte, error)

func (Polygon) String

func (p Polygon) String() string

Formats the coordinate array so that is marshals into valid JSON

func (*Polygon) UnmarshalJSON

func (p *Polygon) UnmarshalJSON(data []byte) error

func (Polygon) Validate

func (p Polygon) Validate() error

Implements the RFC 7946 specifications for a geospatial Polygon [See: 3.1.6 Polygon](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.6)

type RighthandRuleError

type RighthandRuleError struct {
	Angle float64
}

func (*RighthandRuleError) Error

func (e *RighthandRuleError) Error() string

type State

type State struct {
	Name   string  `json:"state"`
	Border Polygon `json:"border"`
}

Represents a geographic state as a name and a geospatial polygon (i.e. a linear ring of boundary coordinates)

func NewState

func NewState(name string, coords []Coordinate) (state State, err error)

Constructor generates a new State object with the provided name and array of coordinates. Translates the coordinates into a [Polyon] object which ensures the state's border is representable as valid GeoJSON

func (State) Contains

func (s State) Contains(coordinate Coordinate) bool

Calls the Contains method for the Polygon object representing the state's border