Support FOV > 180° fisheye camera rendering?

[y-takahashi96]

In the current implementation, the following code seems to restrict the projection range to within a 180° field of view:
gsplat/blob/v1.5.3/gsplat/cuda/include/Cameras.cuh L930-L934

inline __device__ auto camera_ray_to_image_point(
    glm::fvec3 const &cam_ray, float margin_factor
) const -> typename Base::ImagePointReturn {
    if (cam_ray.z <= 0.f)
        return {{0.f, 0.f}, false};
}

This condition appears to discard rays where cam_ray.z <= 0.f, which effectively limits the rendering to the front hemisphere (≤180° FOV).
For fisheye camera models with a very wide field of view (e.g., 200° or more), how can this restriction be removed or modified?

• Is there a recommended approach to handle rays behind the camera?
• Should the projection logic be adjusted, or is there an alternative mapping method for fisheye lenses?

Any guidance or examples would be greatly appreciated.