Hey Simon.aldred,

If you haven’t seen this already, it may be a good place to start: Head-Up Display (HUD) – Ansys Optics.This utilizes both Speos and Zemax OpticStudio to design and optimize a HUD. The link also provides other resources from the Ansys Zemax team that may be useful. 

I think a workflow for designing HUDs is dependent on the designer’s preference. I have used Speos to do initial design and optimization to take advantage of given CAD geometry. From there the design was taken into Zemax OpticStudio for performance optimization. I believe the example provided in the link starts with Zemax OpticStudio and then to Speos. If you have access to both and have used both I would take a look at the HUD analysis tool in Speos and understand its functions and capabilities, then review the additional resources from Zemax on HUDs. A HUD can be done solely on one versus the other, and each one has its benefits and capabilities.  

-Cynthia