Hello Ravi,

Thanks for your question here!

You are right, the unitflag value is used in a different way for Grid Sag and Grid Phase data.

If the Grid file describes a Sag profile, then the unit defined by the unitflag value (i.e. 0 for mm, 1 for cm, 2 for in, and 3 for meters) sets the scale for the z sag and d2z/dxdy cross-derivative values, as well as for the delx and dely increments. The first derivate values are dimensionless and therefore are not scaled.

On the other hand, when the Grid file describes a Phase profile, the units are radians of phase, instead of units of length. In this case, the unitflag data is only used to scale the delx, dely, and derivative values.

Apart from the above, the file format for the Grid Sag and Grid Phase .DAT files are equivalent. You may find example .DAT files in the \Zemax\Objects\Grid Files filder.

To ensure that the DAT file has been properly imported, the Surface Phase analysis tool can be used. Open this analysis by navigating to Analyze…Surface…Phase.

You may find more information about Grid file generation and usage in the following knowledgebase aricles:

How to use the Grid Sag surface type

How to write a Grid Sag DAT file programmatically

Best,

Csilla