"xFov and/or yFov must be set when no aspect ratio is given");
if (this.aspectRatio != null
&& (this.xFov != null && this.yFov != null))
throw new IllegalStateException(
"Only xFov or yFov must be set when aspect ratio is given");
final Perspective perspective = new Perspective(this.zNear, this.zFar);
perspective.setAspectRatio(this.aspectRatio);
perspective.setXFov(this.xFov);
perspective.setYFov(this.yFov);
return perspective;
}