Disappearing Shape

edited May 2013 in Layout
I am trying to design the inverse of a waveguide. For that I have two parts: the area above the waveguide (call it the top) and the area below it (bottom). The empty space between the bottom and top will then serve as the waveguide. The top is a mirror image of the bottom.

Seems simple enough, but I am stumped. I cannot save the bottom without it disappearing. The top is completely fine. Although the bottom shape is still in the saved file (I can use the Tools/Browse Shapes feature to see it) it doesn't recognize it as a shape. When I click on it, KLayout says there are no vertices because there is no shape, and as soon as I close the Browse Shapes window it disappears again.

Here's where it gets good (or from where I am sitting, bad). I figured it was just a fluke, so I simply copied the coordinates of my vertices, opened up a new layout and did it again. The same thing happed. I tried a number of things:
-reversing the order (layer 1 = bottom; layer 2 = top)
-putting them in the same layer
-moving it all to the positive quadrant
-making the two objects as different layers and XORing them together
-saving the bottom by itself

Every single time it saves the top but not the bottom. It is as if the program recognizes one shape as acceptable but its mirror image is unacceptable.

Please help. This is my first time using KLayout and I like it but I can only save half a structure. As you can imagine this is a bit of a downer. Help. Help. Help!

Thanks in advance,


  • edited November -1
    I think I may have figured it out (sort of). It appears as though there is a limit to the number of very long shapes in a file.

    KLayout will not save both shapes if they extend from x=-1.74mm to x=+1.74mm (or larger).
    However, when I save the exact same shapes from x=-1.73mm to x=+1.73mm, both are saved in the GDS II file.
    Does anyone know if this is an inherent property of the GDS format or KLayout itself?

    In case you're interested, it was not an issue of area: Once I found the upper limit of successful saving (x=+/-1.73mm) I extended the shape a little in the y-direction and it still successfully saved both shapes.
  • edited November -1


    there is a limitation to the shape size due to the 32 bit coordinate representation in GDS2. But given a usual database unit of 1nm (0.001), the size that is covered by the 32bit range is in the order of meters!

    What database unit are you using? Maybe you are using a very small one, i.e. 1e-6?



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