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OscarWatch accessibility guidelines

OscarWatch is a desktop satellite tracker (Avalonia). These guidelines keep the app usable for people with low vision, color-vision deficiency, and those who rely on keyboard or screen readers.

Target: WCAG 2.1 Level AA where applicable to a desktop mapping app.

Principles

  1. Perceivable — Text and lines have enough contrast; information is not hue-only.
  2. Operable — Keyboard and focus work for tracking and dialogs.
  3. Understandable — Satellite identity and pass timing are clear in words and numbers.
  4. Robust — Theme-aware resources; automation names on custom controls.

Color blindness and the map

Many users cannot distinguish red vs green or certain cyan/yellow pairs. The tracker shows multiple satellites at once on the world map and sky plot.

Do Don't
Always show satellite names on the map near subpoints Rely on dot color alone to tell ISS from SO-50
Use a fixed, documented palette (PlotColors.cs) tuned for common CVD types Add random bright colors per build
Pair “AOS in …” text with green highlight for imminent passes Use only green text for “soon”
Mark stale TLEs with “stale” text (and color) Orange dot only

Recommended palette family: Okabe–Ito (8 colors, color-blind safe). When changing colors, check with a simulator (e.g. Chrome DevTools vision deficiency, or Coblis).

Contrast (light and dark theme)

The app supports System / Light / Dark (AppThemeManager). Any new UI must be verified in both themes.

Element Minimum contrast ratio
Body text (sidebar, settings, pass list) 4.5:1
Large / bold headings (≥14pt bold) 3:1
Sky plot grid, horizon ring, map track strokes 3:1 vs local background
Non-text focus ring Visible in both themes

Implemented in code:

  • Okabe–Ito palette in PlotColors.cs
  • Theme-aware PassHighlightBrush and StaleTleForegroundBrush (AccessibilityThemeResources)
  • Map/sky markers: dark + white outline; dashed outline below minimum elevation on sky plot
  • Ground station: theme-aware blue marker with dark halo
  • Automation names and keyboard selection on map/sky plot

Tools: WebAIM Contrast Checker, or APCA for very small text.

Typography

Use Size
Live telemetry, pass times, settings fields ≥12px
Hints (“Click a satellite…”) 10–11px OK if not sole instruction
Map labels ≥11px, high-contrast fill behind text (MapLabelBackground)

Respect OS text scaling; avoid clipping in fixed-height sidebars when possible.

Keyboard and focus

  • Tab through menu, map, sky plot, pass list.
  • Focused satellite should match click selection (FocusedNoradId).
  • Settings / pass planner / picker: standard dialog keys (Escape, default button).

Screen readers

Custom controls should expose:

  • Name: e.g. “World map, 3 satellites”
  • Focus: selected satellite name and live az/el when available

Implementation: Avalonia AutomationProperties on WorldMapControl and SkyPlotControl (incremental). PassElevationTimelineControl exposes a summary name via PassElevationTimelineAutomationPeer (pass count and AOS–LOS ranges for visible passes).

What we are not (yet)

Planned improvements (not required for every PR):

  • High contrast theme variant
  • UI scale setting (125% / 150%)
  • Shape or pattern per satellite in addition to color
  • Full WCAG audit of every dialog

Manual test checklist

Before release or after UI changes:

  • Light theme: read sidebar and pass planner without strain
  • Dark theme: same
  • Simulate deuteranopia: still tell satellites apart on map + sky plot
  • Keyboard-only: select satellite, open Settings, close with Escape
  • Pass elevation timeline: click to focus; resize grip; hide/show via Window menu
  • 125% OS display scaling: no clipped pass rows

References

Developer rule for Cursor: .cursor/rules/accessibility.mdc.