Precompute Option

The Precompute option helps you determine the best optical path to choose.

When using the Precompute option, the optical path (position and orientation of mirrors) is optimized to reach an optimal optical quality for the virtual image while using almost the maximum surface of the PGU (according to the ratio specified in the PGU Usage).

Be aware that the Precompute option does not take into account the manufacturing of the bulk. The option gives you start to refine the design. This is what you will see in the following sections.

Important: The Precompute only works with one freeform mirror and a planar fold mirror.

Before Precompute

Before the Precompute action, the input values are manually defined for the mirrors and the PGU.



After Precompute: without modification

The Precompute optimizes the distances between the freeform mirror and the PGU center (distance from freeform mirror to the fold mirror plus the distance from the fold mirror to the PGU center) and the orientation angles of the freeform mirror, fold mirror, and PGU:
  • The PGU plane is oriented to be orthogonal to the optical axis segment joining the fold mirror to the PGU center. This means that the Horizontal angle and Vertical angle of the Fold mirror and PGU are identical after running the Precompute.
  • The Precompute splits the distance between the freeform mirror and the PGU center in two equal values. The sum of these distances guaranties that the PGU usage is correct.




After Precompute: with modifications

The Precompute option does not anticipate potential intersections between the optical axis and mirrors. This may lead to configuration in which for instance the PGU is behind the freeform mirror, which is physically inconsistent.

To bypass such invalid configurations while keeping the Precompute benefits, two actions can be done:

  • The two equal distances can be modified keeping the sum constant.

    Example: the Precompute gives 98 mm for both freeform-fold mirror and fold mirror-PGU distances. This means the overall distance from the imaging mirror to the PGU center is 196 mm. You can increase the first distance to 120 mm to put the fold mirror far away from the imaging mirror. Then, you must reduce the second distance to 76 mm to keep the sum equals to 196 mm.

  • The angles associated to the fold mirror and the PGU orientation can be modified to reorientate the PGU in 3D space using the four corresponding angles. To stricly conserve the Precompute benefits, the angles set to the fold mirror must be identical to the angles applied to the PGU (this keeps the PGU plane orthogonal to the segment fold mirror-PGU).