Reconstructed bird contour with Fourier epicycle circles

The program resamples an ordered closed contour by arc length and computes its complex Fourier coefficients. It selects the largest components to reconstruct the drawing; the local browser animates the same vector sum and updates the curve when harmonic count changes. Fourier analysis, preview playback and export run locally without generation calls. Contour size and harmonic count determine computation; no generated picture is required for the default outline.

Needs
Python 3

v1.0.0 · Updated Oct 25, 2026 · 152 KB · Use it for personal and client work; please don't resell or share the package.

What you get

  1. Reconstruction PNG and editable vector SVG

  2. Interactive circle-orbit viewer with current-curve SVG export

  3. Fourier coefficient ledger and portable contour brief

Good for

  • Explaining a drawing through moving circles
  • Exploring simple versus detailed line reconstructions

Not for

  • Automatic tracing of arbitrary raster images
  • Automatic conversion of disconnected paths or holes into one contour

How it works

Includes a local renderer

  1. Choose the input

    Supply one ordered outline and choose the harmonic count.

  2. Render and inspect

    Inspect the static reconstruction, then play the vector orbit if wanted.

  3. Adjust and export

    Change the harmonic slider and export the current SVG curve.

How the workflow runs

How Fourier line orbit works

The program resamples an ordered closed contour by arc length and computes its complex Fourier coefficients. It selects the largest components to reconstruct the drawing; the local browser animates the same vector sum and updates the curve when harmonic count changes.

What's inside the skill

What you can change

  • points: 8–2048 normalized contour coordinates
  • harmonics: 3–120 coefficients
  • phase: 0–1 and stroke_width: 0.5–5
  • Three-color palette and output dimensions

What to review before delivery

  • The ledger retains 120 ranked coefficients from 512 resampled points.
  • A nine-harmonic version changes the actual reconstruction.
  • The saved brief reproduces the PNG and SVG; unsafe replacement is rejected.

See the package files

These are selected working files from this edition, with their actual role. The complete download also contains instructions and applicable license notices.

  • The domain algorithm and invariant checks.

    scripts/recipe.py
  • Runnable, editable example parameters.

    examples/brief.json
  • Control meanings, proof interpretation and limits.

    references/design-notes.md

Why use this skill

Start with this package

The package connects contour resampling, Fourier analysis, orbit playback and current-state export. A pre-rendered animation or a decorative circle overlay would not provide that editable reconstruction.

Compare the options

A prompt, your own skill, or this workflow?

Start with a prompt

Your agent can create from a plain request. The brief, visual rules, asset choices, output format and review process still need to be established for that project.

Write your own skill

You choose and maintain the reusable instructions, defaults, file structure and checks. This is useful when your process needs different rules or integrations.

A workflow created for PopNow

This workflow was built for PopNow. Its source files, included dependencies and applicable notices are part of the package; the scope described below belongs to this edition.

Guide reviewed Oct 25, 2026

What will this cost?

Fourier analysis, preview playback and export run locally without generation calls. Contour size and harmonic count determine computation; no generated picture is required for the default outline.

The supplied route runs locally. A new-media request is a separate choice. Free skill. New media is quoted before it runs.

The skill package

Free to install under your account's download allowance. The package license covers your own and client work; redistribution is excluded.

Existing assets and local work

Reusing suitable assets, editing files and running local assembly do not call a PopNow generation model. Your computer and any required runtime still do the work.

Your agent and hosting

Any subscription, hosted computer, deployment or other provider fee belongs to that service. Installing this skill does not include those services.

How PopNow billing works

Connections using a PopNow API key, including API-key MCP connections, spend from the separate API balance in USD. A ChatGPT or Claude connection authorized through OAuth spends website credits. These balances are separate; the quote shown by your connection is the approval basis.

Download allowances and current account conditions apply. A free package does not mean unlimited free generation.

How to use it

You say

  • Use the PopNow skill "Fourier line orbit" (fourier-line-orbit) for this: Supply one ordered outline and choose the harmonic count. Use the packaged example as a starting point and return the actual artwork with its editable inputs.

Then try

  • Rebuild a visibly different version using harmonics: 46 → 9.

  • Explain the result using its actual proof files and algorithm ledger.

What to have ready

  • An ordered closed outline, or the included hummingbird contour
  • Python 3.10+, Pillow and NumPy
  • A browser for harmonic controls and animation

Similar skills

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Questions

Do the circles really reconstruct the line?

Yes. Their radii, frequencies and starting phases come from the contour's complex Fourier transform. The endpoint follows the summed vectors; the coefficient ledger records the same values used in the browser.

Does the SVG export use my current setting?

Save current SVG recomputes the closed curve with the selected harmonic count. The main download remains the packaged default artwork; the interactive export is a separate current-curve file.

What costs depend on this workflow?

Fourier analysis, preview playback and export run locally without generation calls. Contour size and harmonic count determine computation; no generated picture is required for the default outline.

What is already packaged in Fourier line orbit?

The domain algorithm and invariant checks. Runnable, editable example parameters. Control meanings, proof interpretation and limits.

Which parts of Fourier line orbit can add a charge?

Fourier analysis, preview playback and export run locally without generation calls. Contour size and harmonic count determine computation; no generated picture is required for the default outline. Connections using a PopNow API key, including API-key MCP connections, spend from the separate API balance in USD. A ChatGPT or Claude connection authorized through OAuth spends website credits. These balances are separate; the quote shown by your connection is the approval basis.

How does Fourier line orbit differ from writing a prompt or my own skill?

The package connects contour resampling, Fourier analysis, orbit playback and current-state export. A pre-rendered animation or a decorative circle overlay would not provide that editable reconstruction.