Speos is a great tool to analyze the performance of a Head-up Display. Once the system has been designed in OpticStudio, it can be exported to Speos using a STEP file. The system performance can then be computed using the HOA tool (HUD Optical Analysis). Note that this feature requires Speos HUD Design and Analysis add-on and Premium or Enterprise license.

Authored By Sandrine Auriol

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Description of the HUD

The HUD presented here is the one used in the article Which tools to use when working on a Head-up-Display?. The sketch below summarizes the characteristics of the HUD system.

Preparing OpticStudio sequential file

To ease the import of 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.

Open the file “HUD_Step1_MF_after_optim.zar”.
Open the properties of the Object. Add a rectangular aperture:

Open the properties of the Image. Add a rectangular aperture:
Horizontal size = 28mm
Vertical size = 28mm

The file with the aperture is in the attachments and is called HUD_Step1_MF_after_optim_apertures.zar.

The size of the mirrors in the original file were too small so here are the new sizes after checking the Footprint diagram.
Freeform mirror: Original and new size

Fold mirror: Original and new size

Export OpticStudio to CAD file

OpticStudio model is going to be converted to a CAD file and then imported into Speos.
Before exporting the CAD model, check the Global Coordinate Reference Surface as it will be used for the CAD origin.

In OpticStudio, export the design to a CAD file:

To make all surfaces available in Speos, select “Export Dummy Surfaces” with a Dummy Thickness of 1. 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 check the performance of the OpticStudio model with built-in surfaces compared to the CAD model. The file called “HUD_Step1_MF_after_optim_CAD.zar” can be found in the attachments. It contains 2 configurations.
- Configuration 1 is the built-in model.
- 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. In the file, the STOP size is set to a diameter of 4mm to model the eye pupil.

The STEP file is a good description of our HUD.

Import CAD file into Speos

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

Then open the CAD file:

The structure will look like this in Speos. Compared to 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. But the Speos navigation can be customized. It can’t be identical to the OpticStudio navigation but here are the settings that were found helpful in this article:

Action	Description	OpticStudio	Speos
Spin	Rotate the view, an object or a group of objects	Hold Left Mouse Button (LMB)	Hold Right Mouse Button (RMB)
Pan	Moving the view up, down, left or right	Hold Middle Mouse Button (MMB)	CTRL + Hold Middle Mouse Button (MMB) +
Zoom	Zoom in and out of the view	Scrolling the mouse wheel	Scrolling the mouse wheel

The navigation settings are described in 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
• Specific car manufacturer’s optical metrics definition and acceptance criteria when using 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 HOA tool is intuitive as each item of the HOA has to be defined in order to run the analysis.

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.

Then the set-up includes the Eyebox, the Target Image, the Windshield, the Mirrors, the PGU. For each item, the user enters criteria that can be read from OpticStudio and select the relevant objects. The Speos file can be found in the attachments.
For more details on the Speos set-up, have a look at the video (coming soon!).

Warping

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

This “deformed grid” is then used as 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:

Above, the warping algorithm is set to disabled. 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 in pixels the warping of the PGU.

In OpticStudio

The warping can be computed in OpticStudio in the backward model (Step 1: From Virtual Image to Display (Backward)) by sampling the field of view on the virtual image and checking where the images of these fields land on the PGU. The image simulation can give a visual result, the Full Field Spot Diagram can shows the spot for each field but to get a numeric output, the Universal Plot 2D can be a good choice:

It 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 given below:
Pixel_x = round((CENX + PGU_Xsize/2) * Pixel_x_size,0)
Pixel_y = round((CENY + PGU_Ysize/2) * Pixel_y_size,0)

Conclusion

This article 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.