This guide explains how to use GhostViewer from start to finish, including what each feature is for.

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What GhostViewer Does

GhostViewer helps you compare an old photo with a new photo of the same place.
You align matching landmarks so you can see “then vs now” as an overlay.

Typical use cases:

• Local history comparisons
• Heritage walks
• Before/after location documentation
• Rephotography projects

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Quick Start (5 Steps)

1. Load an old photo (Step 1).
2. Add a new photo of the same place (Step 2).
3. Match landmarks on both images (Step 3).
4. Align images (Step 4).
5. Review/output and save your result (Step 5).

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Step 1 – Load Old Photo

Use any of these sources:

• a) File upload
  Upload a historical image from your device.
• b) GhostViewer (GV) map
  Opens the archive map in a new tab to help find source images.
• c) Geograph import panel
  Search Geograph and load an image directly into the old photo slot.

Old Photo Tools

• Crop / Straighten
  Improves alignment quality by fixing framing or tilt before matching points.
• Date of photo and age label
  Shows taken date/year when available.
• Distance from search location
  If imported through Geograph with a location context, shows how far away the source image is (metric).

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Geograph Import (inside Step 1)

Search Inputs

• Location (required)
  Town, coordinates, or place text.
• Use my location
  Uses browser geolocation for local searching.
• What to find (optional)
  Keyword filter (for example: church, bridge, station).
• Year max
  Limits results by capture year.

Result Actions

• Preview
  Preview the image before loading.
• Use as old photo
  Loads the selected image into Step 1.
• Save to GV archive
  Saves as a draft old photo in the GhostViewer archive workflow.
• Source (new tab)
  Opens original source URL for attribution/reference.

Geograph Notes

• Attribution must be preserved when reusing Geograph images.
• Distance labels are shown in meters/kilometers where location data is available.

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Step 2 – Add New Photo

Add a current photo of the same place using:

• Take Photo
• Photo Library
• Choose File
• Ghost Guide Camera (when old photo is loaded)

Step 2 Tools

• Ghost Guide Camera
  Camera mode with ghosted old-photo reference to help match angle/composition.
• Crop / Straighten
  Improves final alignment by correcting orientation/frame.

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Step 3 – Match Landmarks

You place matching points on both images:

• Start with at least 4 point pairs.
• Better quality usually comes from 6-8 well-spread points.
• Use corners and center landmarks (not clustered points).
• Pick stable, high-contrast features (window corners, roof lines, signs, edges).

Step 3 Controls

• Start Selecting Landmarks
• Undo / Undo Last
• Add More Points
• Clear All

Step 3 Feedback

• Matched points list (with coordinates)
• Point spread warning when points are too clustered
• Quick low-res warp preview before final alignment

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Step 4 – Align Images

Click Align Images after adding enough matched points.

Transform Modes

• Similarity
  Shift + rotate + scale. Best first choice.
• Affine
  Adds shear. Useful when image angle differs more.
• Perspective
  Handles stronger viewpoint changes. Needs good point coverage.

Optional Setting

• Crop overlay to matched area
  Hides old-image regions outside the matched polygon.

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Step 5 – Output and Review

After alignment:

• View the overlay result.
• Check alignment quality badge and per-point error values.
• Open warp diagnostics for deeper troubleshooting.
• Re-run with a different mode if needed.
• Adjust points and align again.

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Project Saving and Loading

When signed in (Supabase configured):

• Save stores current project state.
• Project titles are used for saved entries.
• My Projects opens saved list.
• Open restores a project.
• Delete removes a saved project.

Privacy consent is required once before cloud project storage.

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Safety and Navigation Features

• Start Over
  Clears loaded photos and workflow state.
• Unsaved-work guard
  Browser warning appears if you try to close/leave with unsaved work in progress.
• External links (Help, Usage Policy, map/source links)
  Open in new tabs.

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Help, Policy, and Community

• Help: https://ghostviewer.co.uk/documentation/
• Usage Policy: https://ghostviewer.co.uk/docs/terms-usage-policies/ghostviewer-usage-policy/usage-policy/
• Facebook Group: available from the app footer

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Troubleshooting Tips

• Misalignment: add more evenly spread landmarks and retry.
• Strong angle differences: try Perspective.
• Warped edges: crop/straighten inputs first, then rematch points.
• Poor Geograph results: refine location text or add keyword.

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Feature Summary (At a Glance)

• Multi-source old photo loading (file, GV map, Geograph)
• New photo capture/import options
• Ghost Guide Camera for field framing
• Landmark-based alignment with transform modes
• Live preview and diagnostics
• Metric distance display for location-aware sources
• Project save/load (when authenticated)
• Privacy-aware browser-first processing