Introduction

Rondel is a circular barcode format that encodes text into concentric ring patterns. It includes encoding, rendering, ML-based detection, and Reed-Solomon error correction.

What is a Rondel?

A Rondel is a 2D barcode arranged as concentric rings of arc segments around a central dot. Each arc represents one bit — dark for 1, light for 0. The format is designed for:

• Aesthetic integration — circular codes blend naturally into designs, logos, and printed media
• Robust scanning — ML detection with Hough circle fallback, perspective correction, and multi-frame consensus
• Error resilience — Reed-Solomon coding over GF(256) corrects up to eccBytes / 2 corrupted bytes
• Zero-config encoding — auto-sizes rings, segments, and ECC for optimal fit

Anatomy of a Rondel

Every rondel has three structural components:

1. Center dot — a solid circle at the geometric center, used as a detection anchor and for sub-pixel center refinement during scanning.
2. Data rings — concentric rings divided into arc segments. The number of segments per ring scales with circumference, keeping arc length constant so inner segments stay readable.
3. Orientation ring — the outermost ring contains a timing pattern (101010) and three asymmetric arcs (large/medium/short) that encode rotation angle, reflection state, and polarity.

Quick Example

import { encode, renderSVG } from "@msalia/rondel";

// Auto-sizes rings, segments, and ECC for optimal fit
const code = encode("https://example.com");

// Render as SVG
const svg = renderSVG(code, {
  size: 400,
  primary: "#1a237e",
  secondary: "#c5cae9",
});

document.body.innerHTML = svg;

Architecture