The imaging system of a head-up display of production-vehicles in automobile industry includes the windshield which is
different for each automobile type. Thus, the the imaging system has to be matched to it. This requires an effcient optic
design procedure in order to minimize the development costs. One challenge is the layout of the freeform surfaces of the
imaging reflectors because there is a lack of procedures comparable to classical imaging systems like first order design or
aberration theory. Additionally, reference systems are not published. Onother big issue is consistent data management. It
is usual practice in automotive industriy that the surface data of the imaging surfaces will be imported in CAD systems.
Often, from these systems manufacturing code is automaticall generated. Importing surface date is delicate, because the
surface describtion in CAD systems is done by NURBS (non-uniform rational B-Splines) which are not or insufficently
implemented in commercial optic design software. Thus, a conversion of the surface is performed by the software tools.
This conversion is normally not much documented and problems with e.g. accuracy, surface continuity often arrise.
In this contribution some methods for the design of an imaging reflector for a head-up display and some resulting designs
are presented. Additionally it is shown that already in the design phase the freeform surface can be described by NURBS
without any lack of performance. This kind of describtion can then easily be transfered to CAD systems by standardized
formats like IGES or STEP without any error-prone conversion.
"Optic design of head-up displays with freeform surfaces specified by NURBS", Proc. SPIE 7100, Optical Design and Engineering III, 71000Y (27 September 2008); doi: 10.1117/12.797761; https://doi.org/10.1117/12.797761