feat: add sensor width constant and update FOV calculation; create .gitignore

.gitignore

@@ -0,0 +1,4 @@
+.DS_Store
+*.ply
+*.settings.json
+__pycache__/

app.py

@@ -33,6 +33,7 @@ DEFAULT_SETTINGS_JSON: Final[Path] = VIEWER_DIR / "settings.default.json"
 DEFAULT_QUEUE_MAX_SIZE: Final[int] = 32
 DEFAULT_FOCAL_LENGTH_MM: Final[float] = 35.0
 SENSOR_HEIGHT_MM: Final[float] = 24.0  # Full-frame 35mm equivalent
+SENSOR_WIDTH_MM: Final[float] = 36.0  # Full-frame 35mm width
 
 # Register static paths for Gradio 6 file serving
 gr.set_static_paths(paths=[str(VIEWER_DIR), str(OUTPUTS_DIR)])
@@ -245,14 +246,16 @@ _ensure_dir(VIEWER_DIR)
 # -----------------------------------------------------------------------------
 
 
-def focal_length_to_fov(focal_length_mm: float, sensor_height_mm: float = SENSOR_HEIGHT_MM) -> float:
-    """Convert focal length (mm) to vertical field of view (degrees).
+def focal_length_to_fov(focal_length_mm: float, sensor_height_mm: float = SENSOR_HEIGHT_MM, sensor_width_mm: float = SENSOR_WIDTH_MM) -> float:
+    """Convert focal length (mm) to diagonal field of view (degrees).
     
-    Uses the formula: FOV = 2 * atan(sensor_height / (2 * focal_length))
+    Uses the formula: FOV = 2 * atan(diagonal / (2 * focal_length))
+    where diagonal = sqrt(width^2 + height^2) for full-frame 35mm (36x24mm)
     """
     if focal_length_mm <= 0:
         focal_length_mm = DEFAULT_FOCAL_LENGTH_MM
-    fov_rad = 2 * math.atan(sensor_height_mm / (2 * focal_length_mm))
+    diagonal_mm = math.sqrt(sensor_width_mm**2 + sensor_height_mm**2)
+    fov_rad = 2 * math.atan(diagonal_mm / (2 * focal_length_mm))
     return math.degrees(fov_rad)
 
 
@@ -264,7 +267,7 @@ def create_settings_file(focal_length_mm: float, output_stem: str) -> Path:
     settings = {
         "camera": {
             "fov": fov,
-            "position": [0, 0, -1],
+            "position": [0, 0, 0],
             "target": [0, 0, 0],
             "startAnim": "none",
             "animTrack": ""