spider

A Go library and CLI tool for generating spider plots (radar charts) with independent axis scales. Unlike traditional radar charts where all axes share the same scale, spider allows each axis to have its own independent scale, making it ideal for comparing metrics with vastly different ranges.

Features

• Independent Axis Scales: Each axis can have its own maximum value, perfect for comparing metrics with different ranges and visualizing tradeoffs
• Flexible Configuration: Create charts programmatically or from JSON/YAML configuration files
• Rich Styling Options: Customize line colors, fill opacity, point shapes, and more
• Automatic Scaling: Auto-calculate axis maximums from series data when not specified
• Tick Configuration: Configurable major and minor ticks with labels
• Legend Support: Customizable legend with multiple placement options
• Multiple Export Formats: Export charts as PNG or SVG
• CLI Tool: Simple command-line interface for generating charts from config files

Installation

go get github.com/aldernero/spider

Quick Start

Using the Library

package main

import (
    "log"
    "github.com/aldernero/spider"
    "github.com/tdewolff/canvas"
    "github.com/tdewolff/canvas/renderers"
)

func main() {
  // Create a chart
  chart := spider.NewChart()
  // add axes
  chart.AddAxis("axis1")
  chart.AddAxis("axis2")
  chart.AddAxis("axis3")
  chart.AddAxis("axis4")
  chart.AddAxis("axis5")
  // add series with datapoints
  chart.AddSeries("series1", map[string]float64{
    "axis1": 1000,
    "axis2": 2.0,
    "axis3": 3.0,
    "axis4": 1000000,
    "axis5": 5.0,
  })
  chart.AddSeries("series2", map[string]float64{
    "axis1": 1500,
    "axis2": 1.0,
    "axis3": 2.5,
    "axis4": 2100000,
    "axis5": 12.0,
  })
  // customize
	chart.Options.Subtitle = "Subtitle"
	chart.Options.Title = "Title"
  // save chart
	if err := chart.Save("output.png"); err != nil {
		log.Fatalf("Failed to save chart: %v", err)
	}
}

The code produces the following spider chart

Using Configuration Files

Create a chart.yaml file:

options:
  connect_type: polygon
  title: "Performance Comparison"

data:
  axes:
    - name: "throughput"
    - name: "latency"
      max: 100
    - name: "cost"

  series:
    - name: "System A"
      data:
        throughput: 1000000
        latency: 50
        cost: 5000

Then use the CLI tool:

go run ./cmd/spider-cli -config chart.yaml -output chart.png

Or build and use the CLI:

go build -o spider-cli ./cmd/spider-cli
./spider-cli -config chart.yaml -output chart.png

Configuration File Format

The library supports both JSON and YAML configuration files. The structure matches the Chart type:

• options: Chart-level settings (width, height, title, plot scale, etc.)
• data.series: Array of data series with styling options
• data.axes: Array of axis definitions with scale and tick configurations

See the examples folder for more details.

Point Shapes

• circle: Circular points (default)
• square: Square points
• triangle: Triangular points
• diamond: Diamond-shaped points
• none: Hide points

Legend Placement

• top, bottom, left, right

API Overview

Core Types

• Chart: Main chart type containing options and data
• Axis: Represents a single axis with scale and tick configuration
• Series: Data series with styling options
• ChartOptions: Chart-level configuration (size, title, legend, etc.)

Key Functions

• NewChart(options, data): Create a chart programmatically
• NewChartFromFile(filename): Load chart from JSON/YAML file
• Save(chart, filename): Save chart to PNG or SVG (auto-detects format)
• SavePNG(chart, filename): Save as PNG
• SaveSVG(chart, filename): Save as SVG

Auto-Max Calculation

If an axis doesn't specify a max value, it will be automatically calculated from the series data with 10% padding. This makes it easy to create charts without manually setting all axis ranges.

Examples

See cmd/main.go for a complete programmatic example, or check the cmd/spider-cli directory for the CLI tool implementation.

Some output from the examples/ folder:

Limitations

• Maximum 50 axes per chart
• Maximum 20 series per chart

License

See LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.