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I am having problems when I use the Rotation transformation for a cell. I have tried making the layout not only using Klayout but also with ipkiss, but i get the same problem in both cases. I create two cells that i want to conect and, before that, i need to rotate one of them in a certain angle (let's say 30º, for example ). The problem is that, after rotating the cell, it seems that each one is refered to a different "mesh" (or like their coordinate systems are slightly displaced, i don't know exactly how to call it) and when i try to place them right next to each other it is impossible to make their shapes match exactly. ¿ How could i solve this problem?

Thank you very much for your help,

Irene

## Comments

Hi Irene,

this is a basic limitation of the GDS format.

GDS stores the coordinates as integers. To obtain the physical dimensions, these coordinates are multiplied with the "database unit". Hence the database unit is the fundamental grid the layout can be drawn on.

When you rotate a cell, the layout which was drawn on the original grid will be rotated. The result will only be compatible with any unrotated layout if the rotation angle is a multiple of 90 degree. For a rotation angle of 30 degree it will not be possible to match the structures.

The usual solution is to let the structures overlap a little. Overlapping is perfectly valid in GDS.

Matthias