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README.md

predict4java Examples

This directory contains practical examples demonstrating how to use the predict4java library for satellite tracking and orbit prediction.

Examples

1. BasicSatelliteTracking.java

Shows how to:

  • Load TLE data for a satellite
  • Define a ground station position
  • Calculate the current position of a satellite
  • Determine if a satellite is visible from your location

Use case: Real-time satellite position tracking

2. PassPrediction.java

Demonstrates:

  • Predicting satellite passes over a ground station
  • Filtering passes by elevation angle
  • Calculating pass duration and timing
  • Finding optimal viewing opportunities

Use case: Planning satellite observations, amateur radio contacts

3. DopplerShiftCalculation.java

Explains how to:

  • Calculate Doppler shift for satellite communications
  • Adjust uplink and downlink frequencies
  • Account for satellite motion in radio communications

Use case: Amateur radio satellite operations, satellite communication systems

4. MultiSatelliteTracking.java

Shows:

  • Tracking multiple satellites simultaneously
  • Comparing positions of different satellites
  • Managing multiple TLE datasets

Use case: Multi-satellite monitoring systems, satellite constellation tracking

Getting Started

Prerequisites

  • Java 11 or higher
  • Maven 3.6 or higher

Maven Dependency

If you want to use predict4java in your own project, add this to your pom.xml:

<dependency>
    <groupId>uk.me.g4dpz</groupId>
    <artifactId>predict4java</artifactId>
    <version>1.2.0</version>
</dependency>

Gradle Dependency

For Gradle projects, add to your build.gradle:

implementation 'uk.me.g4dpz:predict4java:1.2.0'

Compiling and Running

All examples can be easily compiled and run using Maven. The pom.xml file in the examples directory handles all dependencies automatically.

Quick Start

# Navigate to examples directory
cd examples

# Compile and run BasicSatelliteTracking (default)
mvn compile exec:java

# Run a different example by changing the mainClass in pom.xml
# Or use the commands below

Running Each Example

BasicSatelliteTracking:

mvn compile exec:java

(This is the default mainClass in pom.xml)

PassPrediction: Edit pom.xml and change:

<mainClass>BasicSatelliteTracking</mainClass>

to:

<mainClass>PassPrediction</mainClass>

Then run:

mvn compile exec:java

DopplerShiftCalculation: Change mainClass to DopplerShiftCalculation and run:

mvn compile exec:java

MultiSatelliteTracking: Change mainClass to MultiSatelliteTracking and run:

mvn compile exec:java

Clean Build

To start fresh:

mvn clean compile exec:java

Getting TLE Data

TLE (Two-Line Element) data is required for satellite tracking. You can obtain current TLE data from:

Important: TLE data becomes less accurate over time. Update your TLE data regularly (daily for LEO satellites, weekly for higher orbits).

Project Structure

The examples directory contains:

  • *.java - Example source files
  • pom.xml - Maven build configuration with all dependencies
  • README.md - This file
  • target/ - Compiled classes (generated, not in git)

Prerequisites

  • Java 11 or higher
  • Maven 3.6 or higher
  • Internet connection (for downloading dependencies on first run)

The pom.xml automatically handles all dependencies:

  • predict4java 1.2.0
  • Apache Commons Lang3
  • SLF4J API
  • Joda-Time

Understanding the API

Getting Current Satellite Position

The getPositions() method calculates satellite positions over a time range:

List<SatPos> positions = predictor.getPositions(
    referenceDate,      // The reference time
    incrementSeconds,   // Time step between calculations (seconds)
    minutesBefore,      // Minutes before reference time
    minutesAfter        // Minutes after reference time
);

For a single position at the current time, use:

Date now = new Date();
List<SatPos> positions = predictor.getPositions(now, 60, 0, 1);
SatPos position = positions.get(0);  // First position in the list

This calculates positions from now to now + 1 minute in 60-second steps, giving you one position.

Understanding Coordinates

Ground Station Position

  • Latitude: Degrees, North is positive, South is negative (-90 to +90)
  • Longitude: Degrees, East is positive, West is negative (-180 to +180)
  • Altitude: Meters above mean sea level

Satellite Position

  • Azimuth: Compass direction (0° = North, 90° = East, 180° = South, 270° = West)
  • Elevation: Angle above horizon (0° = horizon, 90° = directly overhead)
  • Range: Distance from ground station to satellite (kilometers)
  • Range Rate: Rate of change of range (km/s, negative = approaching, positive = receding)

Tips for Best Results

  1. Update TLE Data Regularly: TLE accuracy degrades over time
  2. Check Elevation Angle: Passes with elevation > 10° are generally good for observation
  3. Account for Obstructions: Trees, buildings, and terrain affect actual visibility
  4. Time Zones: All calculations use UTC internally; convert to local time for display
  5. Doppler Shift: Critical for radio communications; recalculate frequently during a pass

Further Reading

License

These examples are provided under the same MIT license as the predict4java library.

Support

For issues or questions: