Update README.md

Author: MasanoriKanamaru

README.md

@@ -1,3 +1,183 @@
 # FOVSimulator.jl
 
-Julia-based FOV simulator for a spacecraft camera.
+FOVSimulator.jl is a Julia package for simulating camera field of view (FOV) in space missions. It specializes in camera simulations for observing celestial bodies such as asteroids, providing high-precision position and attitude calculations using SPICE kernels and image generation capabilities through ray tracing.
+
+## Features
+
+- High-precision position and attitude calculations for spacecraft, cameras, and celestial bodies using SPICE kernels
+- Ray tracing-based intersection detection for asteroid shape models
+- Thermal image simulation in conjunction with thermophysical models
+- Fast intersection detection algorithms using bounding boxes
+- Support for multiple bodies (e.g., binary asteroid systems)
+
+## Installation
+
+You can install the package using Julia's package manager:
+
+```julia
+using Pkg
+Pkg.add(url="https://github.com/Astroshaper/FOVSimulator.jl")
+```
+
+Or in the package manager mode in Julia REPL (press `]` to enter):
+
+```julia
+] add https://github.com/Astroshaper/FOVSimulator.jl
+```
+
+## Dependencies
+
+- LinearAlgebra
+- Rotations
+- StaticArrays
+- SPICE
+- AsteroidThermoPhysicalModels
+
+## Basic Usage
+
+### 1. Import Required Modules
+
+```julia
+using FOVSimulator
+using SPICE
+```
+
+### 2. Load SPICE Kernels
+
+```julia
+# Load SPICE kernels
+SPICE.furnsh("path/to/kernel/file.tm")
+```
+
+### 3. Set Up Camera
+
+```julia
+# Specify camera NAIF ID, FOV angles, and image size
+camera_id = -12345  # Camera NAIF ID
+fov_angles = (10.0, 8.0)  # FOV angles (width, height) [degrees]
+img_size = (1024, 768)  # Image size (width, height) [pixels]
+
+# Create camera object
+camera = SpiceCamera("CAMERA_NAME", camera_id, fov_angles, img_size)
+```
+
+### 4. Set Up Spacecraft
+
+```julia
+# Create spacecraft object
+spacecraft = SpiceSpacecraft("SPACECRAFT_NAME")
+
+# Mount camera on spacecraft
+add_instrument!(spacecraft, camera)
+```
+
+### 5. Set Up Asteroid
+
+```julia
+# Load shape model
+shape = AsteroidThermoPhysicalModels.load_shape_obj("path/to/shape.obj", scale=1000)  # `scale` factor converts [km] to [m]
+
+# Create asteroid object
+asteroid = SpiceAsteroid("ASTEROID_NAME", shape, "ASTEROID_FIXED_FRAME")
+```
+
+### 6. Update States
+
+```julia
+# Set simulation time
+et = SPICE.str2et("2025-01-01T12:00:00")  # Ephemeris time
+ref = "J2000"  # Reference frame
+abcorr = "NONE"  # Aberration correction flag
+obs = "EARTH"  # Observer
+
+# Update spacecraft and asteroid states
+update!(spacecraft, et, ref, abcorr, obs)
+update!(asteroid, et, ref, abcorr, obs)
+```
+
+### 7. Generate Intersection Map
+
+```julia
+# Perform intersection detection for each pixel
+intersection_map = generate_intersection_map(spacecraft.state.instruments["CAMERA_NAME"], asteroid)
+```
+
+### 8. Generate Image
+
+```julia
+# Generate thermal image using temperature data
+temperatures = fill(300.0, length(asteroid.static.shape.faces))  # Example: set all faces to 300K
+image = generate_image_temperature(intersection_map, temperatures)
+
+# Generate radiance image using emissivity and temperature data
+emissivities = fill(0.9, length(asteroid.static.shape.faces))  # Example: set all faces to 0.9 emissivity
+radiance_image = generate_image_radiance(intersection_map, emissivities, temperatures)
+```
+
+## Advanced Usage
+
+### Binary Asteroid Simulation
+
+```julia
+# Set up primary and secondary asteroids
+primary = SpiceAsteroid("PRIMARY", shape_primary, "PRIMARY_FIXED_FRAME")
+secondary = SpiceAsteroid("SECONDARY", shape_secondary, "SECONDARY_FIXED_FRAME")
+
+# Update states
+update!(spacecraft, et, ref, abcorr, obs)
+update!(primary, et, ref, abcorr, obs)
+update!(secondary, et, ref, abcorr, obs)
+
+# Generate intersection maps
+intersection_map1 = generate_intersection_map(spacecraft.state.instruments["CAMERA_NAME"], primary)
+intersection_map2 = generate_intersection_map(spacecraft.state.instruments["CAMERA_NAME"], secondary)
+
+# Generate thermal image (considering both asteroids)
+image = generate_image_temperature(
+    intersection_map1, temperatures_primary,
+    intersection_map2, temperatures_secondary
+)
+```
+
+### Integration with Thermophysical Models
+
+You can integrate with the AsteroidThermoPhysicalModels package to calculate asteroid surface temperatures and use them for thermal image simulation. See the test file `test/TIRI_image_Didymos.jl` for a detailed example.
+
+## Key Components
+
+### SpiceCamera
+
+Represents a camera model based on SPICE kernels. Manages static camera information (name, ID, FOV shape, etc.) and dynamic state (position, velocity, etc.).
+
+### SpiceSpacecraft
+
+Represents a spacecraft model based on SPICE kernels. Manages static spacecraft information and dynamic state, and can carry multiple instruments (cameras, etc.).
+
+### SpiceAsteroid
+
+Represents an asteroid model based on SPICE kernels. Manages static asteroid information (name, shape model, fixed frame, etc.) and dynamic state (position, velocity, etc.).
+
+### Ray
+
+Represents a ray for ray tracing. Contains an origin point and a direction vector.
+
+### BoundingBox
+
+Represents a bounding box for a shape model. Used to accelerate intersection detection.
+
+### Intersection Detection Functions
+
+- `intersect_ray_triangle`: Detects intersection between a ray and a triangle
+- `intersect_ray_shape`: Detects intersection between a ray and a shape model
+- `intersect_ray_bounding_box`: Detects intersection between a ray and a bounding box
+
+### Image Generation Functions
+
+- `generate_pixel_rays`: Generates rays corresponding to each pixel of a camera
+- `generate_intersection_map`: Generates intersection results for each pixel and an asteroid surface
+- `generate_image_temperature`: Generates a thermal image from intersection results and surface temperatures
+- `generate_image_radiance`: Generates a radiance image from intersection results, emissivities, and surface temperatures
+
+## License
+
+This package is released under the MIT License. See the LICENSE file for details.