> Why don't rotated free pads photo plot?
> Sean James

They *do* photoplot, or at least *should* always photo plot. (And if you
have ever found any occasion when one or more pads have not been
photoplotted, then you have found a bug; in that regard, it is already known
that pads on Mechanical layers are not photoplotted if the Mechanical layer
concerned is selected for inclusion in all plots, and the Gerber file was
created from a *different* layer.)

However, rotated pads (and fills) are usually "drawn" rather than "flashed"
within Gerber files, and that has an impact upon the size of the Gerber
file; it takes a smaller number of characters to specify that an aperture is
"flashed" in a particular location, compared with specifying that an
aperture is to be "drawn" between a start location and an "end" location
(and perhaps one or more intermediate locations).

(I recall discovering, while experimenting, that Protel 99 SE "draws" pads,
rather than "flashing" these, even when the angle of rotation is 90 or 270
degrees (or even 180 degrees as well?). However, there is no good reason why
such pads can't be "flashed".)

The other aspect of "drawing" rotated pads and fills is that the shapes of
these are typically approximated (when the angle of rotation is not an
integral multiple of 90 degrees), rather than being photoplotted in an exact
fashion. As Abdulrahman Lomax has pointed out in another post, it is
possible for Aperture Macro definitions to specify an angle of rotation;
*if* appropriate Aperture Macro definitions were used, rotated pads and
fills then*could* be acurately photoplotted. However, at present, the only
time that Protel uses Aperture Macro definitions in Gerber files is for
thermal relief patterns (used in Gerber files produced from the internal
Power Plane layers).

I am hoping that various aspects of Gerber files will be rectified in
Phoenix (the current name for the next version of Protel). Observations on
rotated pads and fills (with non-orthogonal angles) have been relatively
recent, and thus risk not being rectifed, but various other aspects are also
worthy of attention, and have been pointed out for some time now...

Geoff Harland.
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