Digitize field-by-field: every control, why fill it, what you get

Who this is for

You have a PNG, JPG, WEBP, BMP or a clipboard screenshot of an airfoil drawing. Digitize recovers coordinates. It does not invent precision the image does not contain. Sessions stay ephemeral until you click Create Airfoil.

Correct order (do not skip)

1. Upload or paste the image
2. Tune Preprocess → Apply preprocess
3. Calibration — pick LE then TE (or known chord / axes)
4. Auto detect contours (this is what fills Detected points)
5. Pick the best candidate if several appear
6. Set TE / fit / panel options
7. Reconstruct / fit
8. Read metrics and quality → Create Airfoil

LE/TE alone never create outline points. Apply preprocess alone never creates outline points. Create Airfoil stays grey until Reconstruct / fit has produced coordinates.

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Name

What it is. Display name for the airfoil you will save. Why fill it. So the library and exports are searchable later. Result. Stored on the airfoil record after Create.

Upload / paste

What it is. Source image (PNG / JPG / WEBP / BMP) or Ctrl+V screenshot. Why. Digitize needs pixels; without an image there is nothing to calibrate. Result. A digitize session with a canvas preview. No airfoil yet.

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Preprocess

Brightness (−1 … 1)

Purpose. Shift mid-tones lighter or darker. When to move it. Scans that are overall too dark or washed out. Result after Apply. A retuned binary-ready image — still 0 contour points until Auto detect.

Contrast (0.2 … 3)

Purpose. Stretch ink vs paper so the outline pops. When. Soft pencil drawings or grey backgrounds. Result. Cleaner separation for threshold / adaptive detect.

Threshold (0.05 … 0.95, default ~0.45)

Purpose. Decide what counts as ink vs background (especially in Global mode). When. Too low → noise blobs; too high → broken outline. Result. Changed mask after Apply; still no fitted airfoil until detect + reconstruct.

Invert

Purpose. Flip dark/light when the drawing is white-on-black or a negative. Why. Contour logic assumes ink-like foreground. Result. Correct polarity for detection.

Sharpen

Purpose. Slight edge emphasis on soft scans. Caution. Over-sharpen invents jagged fake edges. Result. Crisper stroke for Edge / Adaptive modes.

Detect mode

Result. Changes *how* Auto detect finds candidates — not the airfoil itself until you run detect.

Gray pick ± tolerance

Purpose. Eyedropper a grey (ice/shade/fill) and isolate that intensity band. Why. Separate a filled silhouette or ice region from background. Result. Isolation on when a pick is set; shown as picked intensity in the UI.

Apply preprocess

Purpose. Push brightness / contrast / threshold / invert / sharpen / detect mode to the session. Critical. This only retunes the image. It does not create Detected points. Click Auto detect contours next.

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Calibration

Mode: LE / TE chord (default)

What to do. Tool LE, click leading edge; tool TE, click trailing edge. Purpose. Define chord direction and scale so pixels become x/c, y/c. Why both are required. Without TE, chord is undefined. Result. Valid calibration — still 0 outline points until detect.

Mode: Known chord length

Field: Chord (mm). Physical chord if you know it. Purpose. Scale when LE/TE are visible but you want millimetre truth. Result. Calibrated scale in engineering units mapped to chord.

Mode: Axes (X0→X1 + Y0)

What to do. Pick X0 (chord start), X1 (chord end), Y0 (upper side). Purpose. Skewed scans without a known chord length. Result. Axis-aligned chord frame for reconstruct.

Accept suggested LE/TE

Purpose. Accept an automatic LE/TE estimate when the session offers one with a confidence label. When. Rough placement is close enough to refine. Result. Calibration filled without hand-picking both ends.

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Tools (quick map)

Undo reverts session history. Simplify contour reduces point noise. Align chord horizontal rotates so chord is flat. Close contour gap bridges small openings. Morphology (open/close/erode/dilate + radius) cleans the mask after preprocess — Apply morphology after choosing an op.

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Auto detect contours

Purpose. Find closed or near-closed outline candidates from the prepared image. Why this is the step people miss. Detected: 0 points after LE/TE means you have not run this yet. Result. Candidate list with point counts and scores. Select the candidate that matches the airfoil (not a title block or border).

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TE / fit / panel (before Reconstruct)

TE mode

Fit mode

Redistribute

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Reconstruct / fit

Purpose. Turn the selected contour + calibration + TE/fit options into airfoil coordinates. Result you should see.

• Reconstructed airfoil plot
• Section metrics: t/c, camber, r_LE/c, TE t/c
• Fit / quality scores (CST residual, suggested polar Mach, suggested AoA window, DAT export score, fairness scores)
• Create Airfoil becomes enabled

If Create is still grey, fit did not produce usable coordinates — re-check candidate, calibration and TE/fit options.

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Create Airfoil — final result

What you get. A saved airfoil in your library with coordinates, metrics and provenance from digitize. Next steps. Run Geometry / Geometry Doctor, then VIC polars like any other section. Digitize quality is a starting point — the geometry gate decides whether analysis may proceed honestly.

Honesty reminder

A beautiful image can still be a bad section. Digitize recovers what was drawn; Geometry Doctor and method IDs keep the trail honest for review.

In simple words: what this page is for

Brightness, threshold, LE/TE, detect mode, TE/fit/panel options — purpose of each Digitize field and the results you should expect before Create Airfoil.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Digitize field-by-field: every control, why fill it, what you get helps you keep a clean trail from shape to polar to choice.

Why the topic matters

Engineers lose time when a title sounds clear but the page only sketches the idea. This article expands Digitize field-by-field: every control, why fill it, what you get so you can answer three questions without jargon: what is the idea, when do you use it, and how do you check it in a HENDOI product.

Read the sections above for the core definitions. Use the steps below to move from reading into a real project trail you can share with a teammate.

How to apply this in HENDOI

In practice: create a HENDOI account or log in, open HENFOIL, bring a section in (create, import DAT, or digitize), pass the geometry gate, climb the analysis ladder only as far as the decision needs, then compare and archive. Every calculated number should keep its method label.

When the section choice is ready for the aircraft, continue in HENSYNTH for mission, compliance and trades. Same account. Same plans.

What this page will not claim: a teaching polar or geometry note is not a flight-Re certificate. HENFOIL labels methods so you know what you bought. Tunnel data and professional judgement still sit outside any single software run.

Checklist before you leave this page

• Can you state the idea of Digitize field-by-field: every control, why fill it, what you get in one sentence?
• Do you know which product owns the next action — HENFOIL or HENSYNTH?
• Will every number you keep carry a method label or a stored-run source?
• If you are new here, have you opened Register or Login?

Related reading on this site

• Airfoil selection with a documented why-#1
• The HENFOIL analysis ladder: when to escalate
• Create airfoil fields: NACA, analytic and CST — what each digit means
• Import and digitize airfoils into HENFOIL
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
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