From 47148200fda91cc063438019d248e4f72906b306 Mon Sep 17 00:00:00 2001
From: Simon Oberzier <simon.oberzier@outlook.de>
Date: Fri, 20 Feb 2026 20:51:56 +0100
Subject: [PATCH] Initial commit

---
 .gitignore   |   1 +
 lib.py       |  42 ++++++++++++++++++
 loop.py      |  97 +++++++++++++++++++++++++++++++++++++++++
 realistic.py | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 260 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 lib.py
 create mode 100644 loop.py
 create mode 100644 realistic.py

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..18a7119
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.rtl
\ No newline at end of file
diff --git a/lib.py b/lib.py
new file mode 100644
index 0000000..984c0f5
--- /dev/null
+++ b/lib.py
@@ -0,0 +1,42 @@
+import struct
+
+class RTLFWriter:
+    HEADER_FIXED_FORMAT = "<4sIII"
+    RECORD_FORMAT = "<dddddddddd"
+
+    MAGIC_NUMBER = b"RTLF"
+    VERSION = 1
+
+    def __init__(self, filename, car_id, track_name):
+        self.filename = filename
+        self.car_id = car_id
+        self.track_name = track_name.encode('utf-8')
+        self.file = open(filename, "wb")
+        self._write_header()
+
+    def _write_header(self):
+        track_len = len(self.track_name)
+        header_bytes = struct.pack(
+            self.HEADER_FIXED_FORMAT,
+            self.MAGIC_NUMBER,
+            self.VERSION,
+            self.car_id,
+            track_len
+        )
+        self.file.write(header_bytes)
+        self.file.write(self.track_name)
+
+    def write_record(self, timestamp, long, lat, fx, fy, fz, ax, ay, az, speed):
+        record_bytes = struct.pack(
+            self.RECORD_FORMAT,
+            timestamp, long, lat, fx, fy, fz, ax, ay, az, speed
+        )
+        self.file.write(record_bytes)
+
+    def close(self):
+        if self.file:
+            self.file.close()
+            self.file = None
+
+    def __enter__(self): return self
+    def __exit__(self, exc_type, exc_val, exc_tb): self.close()
\ No newline at end of file
diff --git a/loop.py b/loop.py
new file mode 100644
index 0000000..3b360e0
--- /dev/null
+++ b/loop.py
@@ -0,0 +1,97 @@
+import math
+import numpy as np
+
+try:
+    from lib import RTLFWriter
+except ImportError:
+    class RTLFWriter:
+        def __init__(self, *args, **kwargs): pass
+        def __enter__(self): return self
+        def __exit__(self, *args): pass
+        def write_record(self, *args): pass
+
+
+def simulate_closed_circuit(filename, car_id=7):
+    track_name = "Closed Circuit GP"
+
+    # Real-world reference point (Silverstone-ish)
+    base_lat = 52.0733
+    base_lon = -1.0147
+
+    dt = 0.05
+    lap_time = 95.0
+    samples = int(lap_time / dt)
+
+    # Track size in METERS (realistic)
+    a = 1200.0   # main straight length scale
+    b = 800.0
+
+    theta = np.linspace(0, 2 * math.pi, samples)
+
+    # Track shape (meters)
+    x_m = (
+        a * np.cos(theta)
+        + 220 * np.cos(3 * theta)
+        + 90 * np.sin(5 * theta)
+    )
+    y_m = (
+        b * np.sin(theta)
+        + 170 * np.sin(2 * theta)
+        - 70 * np.cos(4 * theta)
+    )
+
+    # Convert meters → degrees
+    meters_per_deg_lat = 111_320.0
+    meters_per_deg_lon = meters_per_deg_lat * math.cos(math.radians(base_lat))
+
+    lat = base_lat + (y_m / meters_per_deg_lat)
+    lon = base_lon + (x_m / meters_per_deg_lon)
+
+    # Derivatives (still done in meters for physics)
+    dx = np.gradient(x_m, dt)
+    dy = np.gradient(y_m, dt)
+    ddx = np.gradient(dx, dt)
+    ddy = np.gradient(dy, dt)
+
+    curvature = np.abs(dx * ddy - dy * ddx) / np.power(dx*dx + dy*dy, 1.5)
+    curvature = np.nan_to_num(curvature)
+
+    # Speed profile
+    max_speed = 82.0   # ~295 km/h
+    min_speed = 30.0
+    speed = max_speed - 850 * curvature
+    speed = np.clip(speed, min_speed, max_speed)
+
+    # Acceleration
+    heading_norm = np.hypot(dx, dy)
+    ax = np.gradient(speed * dx / heading_norm, dt)
+    ay = np.gradient(speed * dy / heading_norm, dt)
+    az = np.zeros_like(ax)
+
+    # Forces
+    mass = 1250.0
+    fx = mass * ax
+    fy = mass * ay
+    fz = np.ones_like(fx) * mass * 9.81
+
+    with RTLFWriter(filename, car_id, track_name) as writer:
+        t = 0.0
+        for i in range(samples):
+            writer.write_record(
+                t,
+                float(lon[i]),
+                float(lat[i]),
+                float(fx[i]),
+                float(fy[i]),
+                float(fz[i]),
+                float(ax[i]),
+                float(ay[i]),
+                float(az[i]),
+                float(speed[i])
+            )
+            t += dt
+
+
+if __name__ == "__main__":
+    simulate_closed_circuit("closed_loop.rtl")
+    print("Closed circuit simulation complete.")
\ No newline at end of file
diff --git a/realistic.py b/realistic.py
new file mode 100644
index 0000000..64ca673
--- /dev/null
+++ b/realistic.py
@@ -0,0 +1,120 @@
+import math
+import numpy as np
+
+try:
+    from lib import RTLFWriter
+except ImportError:
+    class RTLFWriter:
+        def __init__(self, *args, **kwargs): pass
+        def __enter__(self): return self
+        def __exit__(self, *args): pass
+        def write_record(self, *args): pass
+
+
+def simulate_closed_circuit(filename, car_id=7):
+    track_name = "FIA constraint GP"
+
+    # === Reference GPS location (realistic) ===
+    base_lat = 52.0733
+    base_lon = -1.0147
+
+    # === Simulation settings ===
+    dt = 0.05
+    lap_time = 92.0
+    samples = int(lap_time / dt)
+
+    # === Track geometry (meters) ===
+    a = 1100.0
+    b = 750.0
+
+    theta = np.linspace(0, 2 * math.pi, samples, endpoint=False)
+
+    x_m = (
+        a * np.cos(theta)
+        + 200 * np.cos(3 * theta)
+        + 70 * np.sin(5 * theta)
+    )
+    y_m = (
+        b * np.sin(theta)
+        + 160 * np.sin(2 * theta)
+        - 60 * np.cos(4 * theta)
+    )
+
+    # === Elevation profile (meters) ===
+    z_m = (
+        12 * np.sin(theta)
+        + 6 * np.sin(3 * theta)
+    )
+
+    # === Derivatives (meters) ===
+    dx = np.gradient(x_m, dt)
+    dy = np.gradient(y_m, dt)
+    ddx = np.gradient(dx, dt)
+    ddy = np.gradient(dy, dt)
+
+    # === Curvature ===
+    curvature = np.abs(dx * ddy - dy * ddx) / np.power(dx*dx + dy*dy, 1.5)
+    curvature = np.nan_to_num(curvature)
+
+    # === Banking angle (radians) ===
+    banking = 0.08 * np.tanh(800 * curvature)
+
+    # === Grip-limited speed model ===
+    g = 9.81
+    mu = 1.6  # racing slicks
+    v_max_curve = np.sqrt((mu * g * (1 + np.sin(banking))) / (curvature + 1e-6))
+
+    speed = np.clip(v_max_curve, 30.0, 83.0)
+
+    # === Acceleration ===
+    norm = np.hypot(dx, dy)
+    vx = speed * dx / norm
+    vy = speed * dy / norm
+
+    ax = np.gradient(vx, dt)
+    ay = np.gradient(vy, dt)
+    az = np.gradient(np.gradient(z_m, dt), dt)
+
+    # === Forces ===
+    mass = 1250.0
+    fx = mass * ax
+    fy = mass * ay
+    fz = mass * (g + az)
+
+    # === Convert meters → lat/long ===
+    meters_per_deg_lat = 111_320.0
+    meters_per_deg_lon = meters_per_deg_lat * math.cos(math.radians(base_lat))
+
+    lat = base_lat + (y_m / meters_per_deg_lat)
+    lon = base_lon + (x_m / meters_per_deg_lon)
+
+    # === OPTIONAL GPS noise (centimeter scale) ===
+    gps_noise_m = 0.25
+    lat += np.random.normal(0, gps_noise_m / meters_per_deg_lat, samples)
+    lon += np.random.normal(0, gps_noise_m / meters_per_deg_lon, samples)
+
+    # === Force exact loop closure ===
+    lat[-1] = lat[0]
+    lon[-1] = lon[0]
+
+    with RTLFWriter(filename, car_id, track_name) as writer:
+        t = 0.0
+        for i in range(samples):
+            writer.write_record(
+                t,
+                float(lon[i]),
+                float(lat[i]),
+                float(fx[i]),
+                float(fy[i]),
+                float(fz[i]),
+                float(ax[i]),
+                float(ay[i]),
+                float(az[i]),
+                float(speed[i])
+            )
+            t += dt
+
+
+if __name__ == "__main__":
+    simulate_closed_circuit("realistic.rtl")
+    print("Realistic simulation complete.")
\ No newline at end of file