Star Chart Calculation and Rendering Implementation

Overview

This document explains the implementation of a real-time star chart calculation and rendering feature for the meteor detection system. The feature uses astrometry.net's solve-field tool to solve for celestial coordinates in camera frames, then renders an overlay of stars and constellations.

Components

1. StarChartOptions (Configuration)

The configuration is stored in the config-example-updated.toml file under the [star_chart] section:

[star_chart]
# Whether the star chart overlay is enabled
enabled = true
# Path to the astrometry.net solve-field binary
solve_field_path = "/usr/local/bin/solve-field"
# Path to the astrometry.net index files
index_path = "/usr/local/share/astrometry"
# Update frequency in seconds
update_frequency = 30.0
# Star marker color (B, G, R, A)
star_color = [0, 255, 0, 255] # Green
# Constellation line color (B, G, R, A)
constellation_color = [0, 180, 0, 180] # Semi-transparent green
# Star marker size
star_size = 3
# Constellation line thickness
line_thickness = 1
# Working directory for temporary files
working_dir = "/tmp/astrometry"
# Whether to show star names
show_star_names = true
# Size of index files to use (in arcminutes)
index_scale_range = [10.0, 60.0]
# Maximum time to wait for solve-field (seconds)
max_solve_time = 60

2. StarChart Module

Created a new module in src/overlay/star_chart.rs with the following components:

StarChart: Main class for handling star chart calculation and rendering
SolutionHint: Stores previous solution data for providing as a hint to future solves
Star and ConstellationLine: Data structures for storing celestial objects
Background thread for running astrometry.net calculations asynchronously

3. Integration with Main Application

The star chart component is integrated into the application in src/app.rs:

Added StarChart to the Application struct
Initialized the StarChart in the initialize() method
Registered a frame hook to apply the star chart overlay
Added shutdown handling for the StarChart

Technical Details

Astrometry.net Integration

The solve-field tool is executed with carefully chosen parameters:

When a previous solution exists, it's used as a hint (ra, dec, radius, scale)
Otherwise, GPS position is used as a general hint
Scale range is provided to limit the search space
A custom configuration file is created for pointing to the index files
Timeout handling prevents hanging on difficult images

Optimization Techniques

Solution Hinting: Each solution is saved and used as a hint for subsequent calculations, significantly improving performance.
Background Processing: Star chart calculations run in a separate thread to avoid blocking the main application.
Frequency Control: Calculations are performed at controlled intervals (configurable via update_frequency), not on every frame.
Timeout Control: Maximum solve time is configurable, preventing hang-ups on difficult frames.

Usage

Ensure astrometry.net is installed with appropriate index files
Configure the [star_chart] section in the config file
The star overlay will be rendered on frames when solutions are available
Adjustments can be made to visualization parameters without restarting

Future Enhancements

Star Catalog Integration: Currently uses a simplified method for rendering stars. Could be enhanced to use a proper star catalog.
Advanced Celestial Rendering: Add more detailed rendering of celestial objects beyond simple stars and constellations.
WCS Library Integration: Replace the simple WCS parsing with a proper WCS library for more accurate coordinate transformations.
Parallel Solving: Allow multiple solves to run in parallel for different regions of the sky.
Sub-Frame Solving: Process smaller sections of the image to improve solve speed.

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