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Waypoint Filtering System

GPS Radar Application - Intelligent Waypoint Display

This document explains the two-strategy waypoint filtering system that intelligently decides which waypoints to display on the radar screen and how to represent off-screen waypoints.

Overview

The GPS Radar uses a dual-strategy filtering system to provide optimal situational awareness while preventing visual clutter:

  1. Distance-Based Filtering (Strategy 1) - Shows waypoints within 10× the current zoom radius
  2. Sector-Based Clustering (Strategy 2) - Shows maximum 8 off-screen indicators (one per direction)

This approach allows users to see waypoints beyond the current zoom level (for navigation planning) while keeping the display clean and performant.

Strategy 1: Distance-Based Filtering

Purpose

Eliminate waypoints that are too far away to be relevant for current navigation while showing points beyond the visible radar range.

Configuration

// include/ui/ui_manager.h:63
static constexpr float DISTANCE_FILTER_MULTIPLIER = 10.0f;

How It Works

Adaptive Distance Threshold:

  • At 10km zoom: Shows waypoints within 100km (10km × 10)
  • At 1km zoom: Shows waypoints within 10km (1km × 10)
  • At 500m zoom: Shows waypoints within 5km (500m × 10)
  • At 100m zoom: Shows waypoints within 1km (100m × 10)
  • At 10m zoom: Shows waypoints within 100m (10m × 10)

Calculation (src/ui/navigation.cpp:296-300):

int zoom_idx = static_cast<int>(ui.current_zoom);
float zoom_radius = ui_manager::RadarConfig::ZOOM_CONFIGS[zoom_idx].radius_meters;
float max_indicator_distance = zoom_radius * ui_manager::RadarConfig::DISTANCE_FILTER_MULTIPLIER;

Filtering Logic (src/ui/navigation.cpp:340-344):

// Calculate distance using Haversine formula (lines 333-338)
if (distance > max_indicator_distance) {
    continue;  // Too far away, not relevant to current navigation
}

Rationale

Why 10× multiplier?

  1. Navigation Planning: See waypoints outside current zoom radius to plan route
  2. Situational Awareness: Know what's ahead without constantly changing zoom
  3. Performance: Eliminates waypoints thousands of km away (e.g., different continents)
  4. User Experience: Balance between "too many indicators" and "missing context"

Example Scenario:

  • User is navigating at 1km zoom (street/neighborhood level)
  • System shows waypoints within 10km radius
  • Off-screen indicators point to destinations in nearby areas
  • User can zoom out to 10km to see all waypoints on-screen

Strategy 2: Sector-Based Clustering

Purpose

Prevent off-screen indicator clutter by showing maximum 8 directional indicators (one per compass direction).

Configuration

// include/ui/ui_manager.h:64-66
static constexpr int MAX_OFFSCREEN_INDICATORS = 8;
static constexpr int INDICATOR_SECTORS = 8;
static constexpr int INDICATOR_SIZE = 15;  // Triangle size (pixels)
static constexpr int INDICATOR_EDGE_INSET = 20;  // Inset from edge (pixels)

How It Works

8-Sector Division (src/ui/navigation.cpp:303-310):

       N (0)
   NW (7)  NE (1)
W (6)         E (2)
   SW (5)  SE (3)
       S (4)

Each sector covers 45° of the compass:

  • Sector 0 (N): 337.5° - 22.5° (North)
  • Sector 1 (NE): 22.5° - 67.5° (Northeast)
  • Sector 2 (E): 67.5° - 112.5° (East)
  • Sector 3 (SE): 112.5° - 157.5° (Southeast)
  • Sector 4 (S): 157.5° - 202.5° (South)
  • Sector 5 (SW): 202.5° - 247.5° (Southwest)
  • Sector 6 (W): 247.5° - 292.5° (West)
  • Sector 7 (NW): 292.5° - 337.5° (Northwest)

Clustering Algorithm (src/ui/navigation.cpp:371-386):

For each off-screen waypoint:

  1. Calculate bearing (direction from user to waypoint)
  2. Convert bearing to sector index (0-7)
  3. Keep only the CLOSEST waypoint per sector
  4. Replace sector's waypoint if new one is closer
// Convert bearing (-π to π) to sector index (0-7)
float bearing_deg = bearing * 180.0f / M_PI_LOCAL;
if (bearing_deg < 0) bearing_deg += 360.0f;

int sector = (int)((bearing_deg + 22.5f) / 45.0f) % NUM_SECTORS;

// Keep closest waypoint per sector
if (distance < sectors[sector].closest_distance) {
    sectors[sector].has_waypoint = true;
    sectors[sector].closest_distance = distance;
    sectors[sector].bearing = bearing;
}

Result: Maximum 8 off-screen indicators, even if 50 waypoints are beyond screen bounds.

Visual Indicators

On-Screen Waypoints

Appearance: Yellow filled circles

  • Size: 25×25 pixels (circular)
  • Color: 0xFFFF00 (bright yellow)
  • Drawing: src/ui/navigation.cpp:365-369
if (x >= 0 && x < screen_size && y >= 0 && y < screen_size) {
    // On-screen: draw yellow circle beacon
    int size = ui_manager::RadarConfig::WAYPOINT_SIZE;  // 25x25
    int half_size = size / 2;
    lv_canvas_draw_rect(canvas, x - half_size, y - half_size, size, size, &circle_dsc);
}

Off-Screen Indicators

Appearance: Orange triangles at screen edge

  • Size: 15 pixels (triangle base)
  • Color: 0xFF8800 (orange - distinct from yellow)
  • Position: 20px inset from circular screen edge
  • Direction: Triangle points toward waypoint bearing
  • Drawing: src/ui/navigation.cpp:250-289
// Position indicator 20px inset from circular edge
int inset = 20;
float edge_x = center_x + (radius - inset) * sin(bearing);
float edge_y = center_y - (radius - inset) * cos(bearing);

// Triangle points outward toward waypoint direction
points[0].x = edge_x + (tri_size * 0.8) * sin(bearing);  // Tip
points[0].y = edge_y - (tri_size * 0.8) * cos(bearing);
// ... left and right base points

Why Orange?

  • Distinct from yellow on-screen beacons (easy differentiation)
  • High visibility against green radar background
  • Clear indication: "waypoint exists in this direction, but off-screen"

Complete Filtering Pipeline

Processing Flow (src/ui/navigation.cpp:291-395)

1. Calculate max_indicator_distance (zoom_radius × 10)
   ↓
2. FOR each waypoint (0 to waypoint_count):
   ↓
3. Calculate distance to waypoint (Haversine formula)
   ↓
4. STRATEGY 1: Distance filtering
   IF distance > max_indicator_distance:
       SKIP waypoint (too far away)
   ↓
5. Calculate bearing (direction from user to waypoint)
   ↓
6. Convert to screen coordinates (lat/lon → x/y pixels)
   ↓
7. Check if on-screen or off-screen:
   ↓
   ├─ ON-SCREEN (x,y within bounds):
   │  └─ Draw yellow circle immediately
   ↓
   └─ OFF-SCREEN:
      └─ STRATEGY 2: Sector clustering
         ├─ Convert bearing to sector (0-7)
         └─ Keep if closest in sector
   ↓
8. Draw off-screen indicators (max 8 triangles)

Example Execution

Scenario: User at 100m zoom with 15 waypoints

Waypoint Distance Status Action
WP1 50m On-screen Draw yellow circle at (x, y)
WP2 80m On-screen Draw yellow circle at (x, y)
WP3 150m Off-screen, Sector N Add to sector 0 (North)
WP4 200m Off-screen, Sector N Replace sector 0 (closer)
WP5 300m Off-screen, Sector E Add to sector 2 (East)
WP6 500m Off-screen, Sector SE Add to sector 3 (Southeast)
... ... ... ...
WP10 1500m Too far Skip (> 1km = 100m × 10)
WP11 5km Too far Skip

Result:

  • 2 yellow circles on screen
  • 3 orange triangles at edge (North, East, Southeast directions)
  • 10 waypoints filtered out (too far away or replaced by closer ones)

Performance Characteristics

Computational Complexity

  • Time Complexity: O(n) where n = waypoint count
  • Single pass: Each waypoint processed once
  • Operations per waypoint:
    • 1× Haversine distance calculation (~20 floating-point ops)
    • 1× bearing calculation (~10 floating-point ops)
    • 1× screen coordinate conversion (~5 floating-point ops)
    • 1× sector assignment (integer division)

Total: ~35 floating-point ops per waypoint

At 50 waypoints: ~1,750 floating-point operations (negligible for ESP32-S3 @ 240MHz)

Memory Usage

  • Sector storage: 8 × SectorWaypoint structs 
    struct SectorWaypoint {
    bool has_waypoint = false;      // 1 byte
    float closest_distance = FLT_MAX; // 4 bytes
    double bearing = 0.0;            // 8 bytes
};  // Total: 13 bytes + 3 padding = 16 bytes
  • Total: 8 × 16 bytes = 128 bytes (stack allocation)

Rendering Performance

  • On-screen waypoints: Direct draw (no limit beyond 50 total)
  • Off-screen indicators: Maximum 8 draws (fixed)
  • Canvas operations: Simple polygon fills (GPU-accelerated)

Frame time impact: <2ms for 50 waypoints at 60 FPS

Configuration and Tuning

Adjusting Distance Multiplier

Current: 10.0× zoom radius

To increase range (show more distant waypoints):

// include/ui/ui_manager.h:63
static constexpr float DISTANCE_FILTER_MULTIPLIER = 20.0f;  // Show 20× zoom radius

To decrease range (focus on nearby waypoints):

static constexpr float DISTANCE_FILTER_MULTIPLIER = 5.0f;  // Show 5× zoom radius

Trade-offs:

  • Higher multiplier: More situational awareness, more off-screen indicators
  • Lower multiplier: Tighter focus, fewer distractions

Changing Sector Count

Current: 8 sectors (cardinal + intercardinal directions)

To increase precision (16 sectors - every 22.5°):

// include/ui/ui_manager.h:64
static constexpr int INDICATOR_SECTORS = 16;
static constexpr int MAX_OFFSCREEN_INDICATORS = 16;

Note: Must update sector calculation in navigation.cpp:378:

int sector = (int)((bearing_deg + 11.25f) / 22.5f) % NUM_SECTORS;

Trade-offs:

  • More sectors: Higher precision, more indicators (may clutter edge)
  • Fewer sectors: Cleaner display, less precise direction info

Integration with Other Systems

Zoom System

  • Filtering automatically adapts to zoom level changes
  • No configuration needed - uses ui.current_zoom state
  • Zoom levels defined in ui_manager.h:71-77

GPX Loader

  • Filtering operates on ui.waypoints[] array
  • GPX loader populates array via gpx_loader::loadAllGPXFiles()
  • Maximum 50 waypoints (ui_manager::RadarConfig::MAX_WAYPOINTS)

Radar Display

  • Called by navigation::updateRadarDisplay() every frame
  • Integrated with grid drawing and center triangle
  • Respects circular screen clipping

Code References

Key Files

  • Algorithm: src/ui/navigation.cpp:291-395 - drawWaypoints() function
  • Configuration: include/ui/ui_manager.h:54-81 - RadarConfig struct
  • Off-screen drawing: src/ui/navigation.cpp:250-289 - drawOffScreenIndicator()
  • Coordinate conversion: src/ui/navigation.cpp:98-135 - latLonToScreen()

Important Constants

// include/ui/ui_manager.h
struct RadarConfig {
    static constexpr int MAX_WAYPOINTS = 50;
    static constexpr int WAYPOINT_SIZE = 25;  // On-screen circle size
    static constexpr int MAX_OFFSCREEN_INDICATORS = 8;
    static constexpr float DISTANCE_FILTER_MULTIPLIER = 10.0f;
    static constexpr int INDICATOR_SECTORS = 8;
    static constexpr int INDICATOR_SIZE = 15;  // Triangle size
    static constexpr int INDICATOR_EDGE_INSET = 20;  // Distance from edge
};

Future Enhancements

Possible Improvements

  1. Adaptive multiplier: Change distance multiplier based on waypoint density
  2. Priority waypoints: Always show certain waypoints regardless of distance
  3. Distance labels: Show distance to off-screen waypoints on indicators
  4. Sector heat map: Color-code indicators by waypoint count in sector
  5. Animation: Pulse effect on indicators when new waypoints appear
  6. Touch interaction: Tap indicator to center map on that direction

Performance Optimizations

  1. Spatial indexing: Use quadtree for O(log n) distance queries (only beneficial >200 waypoints)
  2. Dirty flag: Only recalculate when waypoints change or user moves significantly
  3. GPU acceleration: Offload Haversine calculations to hardware floating-point unit

Summary

The GPS Radar waypoint filtering system provides:

✅ Intelligent range limiting - Shows 10× zoom radius for optimal awareness ✅ Clean visual display - Maximum 8 off-screen indicators prevents clutter ✅ Performance - O(n) algorithm with negligible overhead ✅ Flexibility - Easy to tune via compile-time constants ✅ User experience - See what's outside current zoom for navigation planning

This dual-strategy approach balances situational awareness (knowing what's beyond screen) with visual clarity (not overwhelming the user with 50 indicators).

Last Updated: 2025-10-18 Author: GPS Radar Development Team Related Documentation: README.md, CLAUDE.md, docs/gps_settings_simplification.md