Box records in gdsii files

In gdsii files, what are box records used for? How should they be
interpreted by a gdsii reader? Are they generated by many cad
programs?

I've seen some cadence documentation that says that they should have 5
XY coordinates (similar to a boundary) and other cadence documentation
that says that they are defined by a center coordinate and width and
height. Which is correct?

 

Thank you, but that didn't really answer my question. There seems to
be no readily available information about several things related to box
records:

1-How are boundary and box records different? Why would a cad program
write out a box record instead of a boundary record?
2-What is the meaning of BOXTYPE?
3-There is conflicting cadence documentation on the XY data. One
reference says the XY should have 5 points (I assume the points define
the perimeter of the box) another reference says that the XY data
should contain the center point and height/width information.
4-Are box records generally accepted by cad programs / foundaries? The
mosis website says that box records are read but ignored.

 

The way I understand it, the box record is the same as the boundary record
except that there are exactly 5 points. Boxes are rectangles, and the five
points represent the four corners of the rectangle with the last point
being a duplicate of the first point just like in boundaries: (x1,y1),
(x2,y1), (x2,y2), (x1,y2), (x1,y1).

The boxtype is similar to a datatype (I could find no documented
difference). Some tools might write rectangles as boxes and others might
write them as boundaries. It seems to make sense to use boxes to represent
rectangles and boundaries to represent 4-vertex polygons that are not
rectangles. Or maybe boxes were originally meant to define bounding boxes
or special drawing areas of a layout. I really don't know why there is a
box record or why any program would treat boxes differently than
boundaries. Ignoring boxes seems odd, but you should definitely find out
what your foundary does with boxes and change the record types to
boundaries (and boxtypes to datatypes) if boxes are ignored.

Frank

 

FYI,

File->Export->Stream has an option "Output Rectangle as BOX" (off by default)
and File->Import->Stream has an option "Ignore BOX record" (off by default) to
handle this variability in the comprehension of box records by various other
tools.

Regards,

Andrew.