Advanced Parameters

The Advanced parameters are available for the sole purpose of allowing you to maximize and optimize the optical quality of its system. It is neither compulsory nor needed to use or modify the following parameters to obtain a correctly designed HUD system.

In case of problems during the conception (like a HUD calculation that is too long or results that may not be as precise as expected), they can also assist you in reaching an acceptable solution.

The Mirror Size Ratio optimizes the mirror's size according to how the HUD system has been designed. When the HUD system is optimized/computed, a resizing process starts.

Figure 1. Mirror Size Ratio Before Optimization

Before the optimization, mirrors are considered as planar on an infinite plane. The infinite plane is orthogonal to the bisector of the optical axes defined for the two mirrors. These planar mirrors are based on the projection of the corner’s rays made by the Target Image / Eyebox optical volume on the windshield (Windshield impact zone). Planar mirrors have a ratio equal to 1 and all rays intersect the mirrors.

Figure 2. Mirror Size Ratio After Optimization: Too Small

During the optimization the mirrors shapes are modified and can be warped, and some rays may not intersect the mirrors. In this context the Mirror size ratio can help you anticipate a potential set of non-intersecting rays by the mirrors due to the optimization of the mirror shapes that can be warped.

Figure 3. Mirror Size Ratio After Optimization: Optimized

Thus, in the Speos interface, the default value of the Mirror size ratio is set to 1.3 to anticipate these non-intersecting rays in most cases. However, in some case the Mirror size ratio can be increased to extend the mirrors if rays still do not intersect.

PGU usage adjusts the ratio between the warping and the Picture Generation Unit to optimize the surface used by the warping.

By default the PGU usage is set at 0.95, that means 95% of the PGU is used for the image warping.

The Stopping criterion defines a threshold value representing the degree of precision to be reached for the optimization to end.

The optimization works in a principle of cycles. At each cycle, the result is optimized and the optical quality increases. After a certain number of cycles, the system becomes more and more defined and the improvement gained on a cycle is greatly reduced. When between two cycles, only 0.05% of improvement is achieved, the optimization stops.

The value is expressed in percentage and is, by default, set to 0.005 (0.05 %).

This criteria is useful to optimize computation time and results according to your needs at different stages of the development process of a HUD system. In the early stages of the design process, you can set this criterion relatively high (like 8%) to gain time during optimization. On the contrary, in the final stages of the design process, you can set this criterion low (< 0.005) so that the system is computed with precision.

Figure 4. Improvement obtained between optimization cycles

Curvature Balance pilots the curvature of the first freeform mirror to get the best image quality. If the curvature balance is left unedited (= 0), it is automatically calculated by the algorithm based on the PGU usage.

Figure 5. Curvature balance effect on HUD.

In this figure we consider the 3 states of the Mirror B (B B' B'') as being at the same position.

The percentage represents the percentage of the distance between Freeform Mirror A and PGU. For the Mirror B, d_MirrorA/PGU = d_{MirrorA/PGU image B} or for the Mirror B', 90% * d_MirrorA/PGU = d_{MirrorA/PGU image B'}