Collimated visual display system

A collimated visual display system for providing virtual out of window images surrounding a pilot and/or co-pilot in simulation applications, the system comprising:

• a back-projection screen,
• a spherical mirror reflecting an image on the back-projection screen to be viewed by a viewer located in a design eye point,
• wherein the back-projection screen is configured to provide a collimated beam to a viewer located in the design eye point,
• a single projector illuminating the back-projection screen to provide the image on the back-projection screen,
• a freeform mirror located between the back-projection screen and the projector that is configured to map pixels of the projector to the back-projection screen such that a resolution of the projector is sufficiently uniform on the back-projection screen, whereby the resolution is uniform within a range of +20% of a target resolution.

A method for designing a freeform mirror for a collimated visual display system, wherein the method comprises the steps of:

• a) providing initial values comprising a projector position, a projector orientation, a back-projection screen position, orientation and shape,
• b) providing fixed parameters, said fixed parameters comprising a projector resolution,
• c) defining a reference point on a freeform mirror,
• d) defining a mapping function between pixels of a projector and a target point on a back-projection screen,
• e) defining a normal vector parametric representation of a freeform surface,
• f) optimizing the normal vectors of the freeform surface such that a reflection on the freeform surface of a light ray coming from each pixel of the projector reaches the target point on the back-projection screen, until the optimized freeform surface has been reached,
• g) repeating step f) until the freeform surface provides a target resolution uniformity on the back-projection screen and a target field of view within a predefined tolerance, whereby the resolution is uniform within a range of +20% of a target resolution,
• h) measuring an astigmatism of the reflected light rays hitting the back-projection surface and comparing the measured astigmatism with a threshold,
• i) if the measured astigmatism is higher than the threshold, repeating steps e) to h),
• j) if the measured astigmatism is lower than the threshold, storing a representation of the freeform surface at step g).