Converting Blender FOV to Three.js PerspectiveCamera

The issue you're experiencing with FOV values between Blender and Three.js is likely due to differences in how field of view is calculated and applied in each system.

In Three.js, the PerspectiveCamera.fov property represents the vertical field of view in degrees. However, there are a few important differences to consider:

1. Blender may be using horizontal FOV while Three.js uses vertical FOV
2. Blender may be measuring FOV differently (e.g., from the center to edge vs. edge to edge)
3. The coordinate systems between Blender and Three.js differ

Possible Solutions

To convert the Blender FOV to match Three.js:

1. If Blender is exporting horizontal FOV, you'll need to convert it to vertical FOV:

   JAVASCRIPTCopied
   // Convert horizontal FOV to vertical FOV
   const aspectRatio = width / height;
   const verticalFOV = 2 * Math.atan(Math.tan(horizontalFOV * Math.PI / 360) / aspectRatio) * 180 / Math.PI;

2. Check if the FOV needs to be inverted (if that's what you're observing):

   JAVASCRIPTCopied
   // If FOV appears inverted
   camera.fov = -blenderFOV; // Or some other transformation

3. Make sure you're calling camera.updateProjectionMatrix() after changing the FOV:

   JAVASCRIPTCopied
   camera.fov = convertedFOV;
   camera.updateProjectionMatrix();

Since you mentioned that exporting the full camera from Blender works correctly, you might want to temporarily use that approach and inspect the resulting Three.js camera properties to understand how the FOV is being transformed during the export process.

Without more specific details about the exact values you're seeing, it's difficult to provide the exact conversion formula, but these approaches should help you troubleshoot the issue.