maprender

Documentation

Overview

Package maprender provides a geographic-map placeholder renderer for the go-fastreport MapObject component.

Full vector rendering requires ESRI Shapefile data that is not bundled with the library. This package renders a visually recognisable map-style image:

• Ocean background
• Latitude/longitude graticule grid (every 30°)
• Equator and Prime-Meridian highlight lines
• A simplified world-outline silhouette drawn from a small embedded polygon dataset (major continental outlines only)
• Layer count and palette label in the corner

The output is an image.Image that callers encode to PNG and store in the report BlobStore.

Index

• func Render(opts Options) image.Image
• type Bubble
• type ChoroplethPalette
  • func NamedPalette(name string) ChoroplethPalette
• type GeoFeature
  • func ParseGeoJSON(data []byte) ([]GeoFeature, error)
• type Layer
• type LinearPalette
  • func (p *LinearPalette) Color(t float64) color.NRGBA
• type Options
• type StepPalette
  • func (p *StepPalette) Color(t float64) color.NRGBA

Functions

func Render

func Render(opts Options) image.Image

Render returns a map-style image for the given options. Width and Height default to 400×200 when zero.

Types

type Bubble

type Bubble struct {
	Lon, Lat float64 // centre in degrees
	Value    float64 // controls radius scaling
	Color    color.NRGBA
	Label    string
}

Bubble represents a circle overlay at a geographic position.

type ChoroplethPalette

type ChoroplethPalette interface {
	Color(t float64) color.NRGBA
}

ChoroplethPalette maps a normalised value [0,1] to a color.

func NamedPalette

func NamedPalette(name string) ChoroplethPalette

NamedPalette returns a ChoroplethPalette for common palette names.

type GeoFeature

type GeoFeature struct {
	// ID is the feature identifier (optional — from properties or "id" field).
	ID string
	// Name is a human-readable name (e.g. from properties.name).
	Name string
	// Polygons holds all polygon rings for this feature.
	// Each polygon is a slice of [lon, lat] pairs (exterior ring only).
	Polygons [][][2]float64
	// Value is a numeric data value for choropleth/bubble sizing (set by caller).
	Value float64
	// BubbleLon/BubbleLat is the bubble centre (centroid if not specified).
	BubbleLon, BubbleLat float64
}

GeoFeature is a single GeoJSON Feature.

func ParseGeoJSON

func ParseGeoJSON(data []byte) ([]GeoFeature, error)

ParseGeoJSON decodes a GeoJSON FeatureCollection or Geometry string and returns the extracted features.

type Layer

type Layer struct {
	Shapefile string
	Palette   string
	Type      string // "Choropleth", "Bubble", etc.

	// GeoFeatures contains user-supplied geographic features for this layer.
	// When non-nil, the built-in continental outlines are replaced by these.
	GeoFeatures []GeoFeature

	// Bubbles is the list of bubble overlays for "Bubble" type layers.
	Bubbles []Bubble

	// ShowLegend enables a legend for this layer.
	ShowLegend bool
}

Layer carries the minimal information extracted from a MapLayer that affects how the map is rendered.

type LinearPalette

type LinearPalette struct {
	Low, High color.NRGBA
}

LinearPalette interpolates linearly between two colors.

func (*LinearPalette) Color

func (p *LinearPalette) Color(t float64) color.NRGBA

type Options

type Options struct {
	Width   int
	Height  int
	OffsetX float64 // pan offset in degrees longitude
	OffsetY float64 // pan offset in degrees latitude
	Zoom    float64 // 1.0 = full world (-180..180 × -90..90)
	Layers  []Layer
}

Options control the rendering.

type StepPalette

type StepPalette struct {
	Colors []color.NRGBA
}

StepPalette maps discrete values to colors via a list.

func (*StepPalette) Color

func (p *StepPalette) Color(t float64) color.NRGBA