It is vital that you have confidence in the results that you have obtained from ZEMAX. Especially in Non- Sequential (NS) mode, it is possible to create very complex geometries, with objects inside of other objects, for example. How do you know whether or not you have made a mistake?

Every so often, you may encounter geometry errors when working in NS ZEMAX or within a hybrid, mixed mode design (Mixed Sequential/Non-Sequential Mode). Geometry errors occur when ZEMAX encounters a section of your design where it is not sure how to trace. These errors are issued via the user interface, and are also logged to the ray database when you are performing an analysis with even millions of rays. It is important to understand that the reported errors are designed to GIVE you confidence that your results are correct. By tracking these errors down, you can have confidence that your system results are accurate.

When geometry errors arise, you need to be able to determine where they come from and how to assess them.  There are valuable tools built into ZEMAX (which will be described in this article) that can be used to answer these questions.

As you have probably already guessed, geometry errors are not unique. That is, there is more than one possible scenario or reason as to their existence. In this article, we will cover common reasons for geometry related errors, and illustrate how to locate and fix these errors. Ultimately, these methods may be helpful in diagnosing your own file and aid in determining whether or not the geometry errors require immediate attention. Three of the most frequent causes of geometry related errors are outlined in the table below:

 REASON DESCRIPTION 
INVALID PLACEMENT OF ENTRY & EXIT PORTS Neither the entry or exit ports may intersect with any objects in a Non-Sequential Component (NSC) group.  Nor can the exit port be in direct contact with a surface of a Non-Sequential (NS) object.  It is important to ensure that both the ports are separated by at least the glue distance from any of the objects in the NSC group.
INVALID PLACEMENT OF SOURCES Sources can exist inside of volume objects, but they must be specified as such using the "Inside Of" flag in the NSC Editor.  Sources may not straddle boundaries of volume objects.  Misplaced Source Objects will result in geometry errors.
INVALID CONSTRUCTION OF SOLID OBJECTS Sometimes, user defined objects, such as Polygon Objects or Imported Objects, are improperly defined.  For example, if a Polygon Object is not fully enclosed, ZEMAX cannot determine when a ray left that object and will issue a geometry error.