A Head-Up Display (HUD) is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from a pilot being able to view information with the head positioned "up" and looking forward, instead of angled down looking at lower instruments. A HUD also has the advantage that the pilot's eyes do not need to refocus to view the outside after looking at the nearer instruments in the cockpit.

Although they were initially developed for military aviation, HUDs are now used in commercial aircraft, automobiles, and other (mostly professional) applications.

Head-Up Displays were a precursor technology to augmented reality (AR), incorporating a subset of the features needed for the full AR experience, but lacking the necessary registration and tracking between the virtual content and the user's real-world environment

Ansys Speos is a great tool for analyzing the performance of a Head-Up Display. Once the optical components in the HUD have been designed in Ansys Zemax OpticStudio, they can be exported to Speos where system performance is evaluated using the HOA (HUD Optical Analysis) tool. Note that this feature requires the Speos HUD Design and Analysis add-on and a Speos Premium or Enterprise license.

The HUD presented here is the one used in the Knowledgebase article Which tools to use when working on a Head-up-Display?, which reviews the workflow for designing the HUD components in Ansys Zemax OpticStudio. The sketch below summarizes the key components of the HUD system.

Preparing OpticStudio sequential file

To ease the import of the OpticStudio sequential design into Speos, we are going to add:

• A rectangular aperture at the object. The object is the virtual image of the HUD. That rectangular aperture will show the size of the field of view.

  

• A rectangular aperture at the PGU (located at the Image surface).

• Horizontal size = 28mm, Vertical size = 28mm

After checking the Footprint diagram the mirrors in the original file were found to be too small to capture the full beam, so their sizes are updated prior to importing the model into Speos.

Freeform mirror: Original and new size

Fold mirror: Original and new size

Export OpticStudio model to CAD file

The OpticStudio model is converted to a CAD file and then imported into Speos.
Before exporting the CAD model we set the Global Coordinate Reference Surface to the object plane, as this will be used for the CAD origin.

Then we export the design to a CAD file:

It can also be interesting to export rays to give a comparison.

Checking the CAD accuracy

Before moving on to Speos, a comparison can be run inside OpticStudio to compare the performance of the OpticStudio model with built-in (native parametric) surfaces compared to that with the CAD model. We do this by setting up a multi-configuration model in OpticStudio with 2 different configurations.

• Configuration 1 uses the built-in surfaces.

• Configuration 2 contains a Non-Sequential Component surface with a CAD export of the model.

The results can be compared between both configurations with analyses like the Configuration Matrix Spot Diagram. The stop size is set to a diameter of 4mm to model the eye pupil.

The comparison demonstrates that the CAD model provides a good description of our HUD system in this case.

Import CAD file into Speos

Once in Speos, we check the import settings under File…Speos Options…File Options…General:

Then open the CAD file:

The structure will look like the following in Speos. Compared to the OpticStudio lens data editor, the names of the objects are the names of the lines:

Speos navigation for OpticStudio users

Interacting with objects in Speos is different from interacting with objects in OpticStudio. The Speos navigation can be customized and, while it can’t be identical to the OpticStudio navigation, here are the settings that we found were helpful for this example:

The navigation settings are described in the Speos Getting Started Guide, which is a useful resource for new users.

HUD Optical Analysis (HOA) in Speos

HOA allows to quantify the quality of the virtual image of automotive head-up displays. It can compute:

• Virtual image distance, look down angle, look over angle, field of view

• Distortion, smile, trapeze, torsion, magnification, rotation, divergence, etc.

• Ghost

• Field curvature, spot size, astigmatism

• Optical metrics definition and acceptance criteria for specific car manufacturers, by using dedicated plugins.

• Warping data to feed pre-distortion image correction (warping information can also be imported).

Once the CAD file has been imported into Speos, the HOA can be run without defining any sources or materials. 

The first step is to define the axes for the HOA. In the OpticStudio design, Z Axis is the Vehicle Direction and Y Axis is the Top Direction.

The set-up includes the Eyebox, the Target Image, the Windshield, the Mirrors, the PGU. For each item, .

Warping

One output from the HOA is warping. Let’s compare this metric in both software for a sanity check. The warping is a grid on the PGU representing how the image is distorted by the optical system.

This “deformed grid” is then used in a post processing step to correct the optical aberrations of the system. The PGU displays a “deformed” image to provide an optimal target image for the driver.

In Speos

In the HOA analysis, the warping settings are:

In this case, the warping algorithm is set to Disable. This setting is needed to interpolate the final image. Run the HOA and check the results.

Once run, the file is saved under Speos output files. It gives the warping of the PGU, in pixels.

In OpticStudio

The warping can be computed in the OpticStudio model () by sampling the field of view on the virtual image and checking where the images of these field points land on the PGU. The Image Simulation analysis gives a visual result, and the Full Field Spot Diagram shows the spot for each field but, to get a numeric output, the Universal Plot 2D is a good choice:

This plot can be run twice, once with the CENX operand to get the X-coordinate of the centroid/average point of the field of view and another time with CENY for the Y-coordinate.

The results are given in mm in the local coordinate of the image plane (surface 12). Speos gives the results in pixels.

The conversion between pixels and coordinates is:

• Pixel_x = round((CENX + PGU_Xsize/2) * Pixel_x_size,0)

• Pixel_y = round((CENY + PGU_Ysize/2) * Pixel_y_size,0)

Conclusion

This blog has highlighted the steps to export a HUD design from OpticStudio into Speos. Speos HOA is a great tool to get a full report on a designed HUD.

Find the full article and downloadable sample files on our Knowledgebase here.

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Author:
Sandrine Auriol
Lead Application Engineer
Ansys