Thanks for y= our detailed response.

I did some more tests.=C2=A0

I= t appears that the absolute position is written to the footprint origin
=

value in the footprint file.=C2=A0 I wrote one origin to 2870.00= mil and 1525.00mil.

I did this by placing the component - set= ting the cursor to the same location as the diamond
and coincident with = Ctl-M, and saving a new footprint. I was surprised by the results and I hav= e
no idea why a absolute position would have any value=C2=A0 - especial= ly if your PCB outline was smaller
then these dimensions.

Based on your latest comments about using absolute coordinates in the = past=C2=A0 - could what
I have been seeing with the footprint origin=C2= =A0 - is this a legacy 'feature' that has been made non-functional =
with new PCB releases?

If I hand edit the origi= n back to (0,0) in the footprint file and restart PCB and place the
sam= e component at the cursor - no problem.=C2=A0 I experience no difference us= ing this component
in PCB. And as I mentioned previously, I find other = library footprints with non-zero origin values also.

(however= , there are differences in the "Elements[ ]" arguments).

I'd like to suggest that before more speculations= are made on how it should work - please test in your version of PCB.=C2=A0=
I may have something particular with my environment. Testing origin va= lues can be done easily/quickly.

Dave

On= Mon, Aug 17, 2015 at 4:06 PM, DJ Delorie <dj AT delorie DOT com> wrot= e:

> A lot of this doesn't make sense. I'm hearing 2 things.

As a bit of background, consider that the original footprint "f= ile"
allowed more than one footprint, and we use the same information for
cut buffers and "save buffer to file" stuff.=C2=A0 Each pcb, past= e buffer,
and file has its own local coordinate system, and cutting and pasting
translates between those coordinate systems.

> 1) If the 0,0 origin coordinates are an absolute position from the

Keep in mind the difference between a footprint and an element.

A footprint is a pattern in a library.

An element is a specified instance of a footprint along with other
information.

So it makes no sense to talk about the "origin" of a footprint - = it's
in a library, it's just a pattern, the only magic about the origin is that it's the mathematical 0,0 point that other things in the
footprint are measured from.

When you paste a footprint onto a pcb it becomes an element.=C2=A0 At that<= br> point, the 0,0 of the footprint is mapped to wherever the crosshair
is, and becomes the "location" of the element.

= =C2=A0
That has not been seen by my experiments.=C2=A0 The value for the= footprint origin
does not appear to matter.=C2=A0

> But that doesn't happen when you import schematics to the PCB.

Actually it does if you use gsch2pcb.=C2=A0 The File->Import meth= od
relocates every element so that they're not all up in the corner.

> The diamond shape origin is in the center of this 805 component - no > matter where this component is randomly placed onto the PCB grid.
> The component origin cannot be linked to absolute PCB coordinates.

The element's internal measurements are all relative to the elem= ent's
origin, as if it had its own local coordinate system.=C2=A0 We do this just=
to keep the internal logic easier.=C2=A0 We *used* to keep the internal
coordinates absolute, and had to recalculate the position of every
pin, pad, and silk every time you moved the element.

> 2) I thought I heard that the origin written to the footprint file, > happens to be the absolute position of the cursor when captured into > the buffer.

When you're editing a footprint via pcb, at one point you "= cut
selected objects to buffer".=C2=A0 At that moment, the location of the=
crosshair becomes the 0,0 point for the coordinate system that the cut
buffer uses.=C2=A0 If you paste the buffer as-is, you'll notice that th= e
"ghost" image before you click is relative to the crosshair in th= e
same way it was relative to when you cut it.

When you convert a buffer to a footprint, the footprint is created
relative to the 0,0 of the buffer, of course.=C2=A0 The *net* result is
that the location of the crosshair when you initially cut it becomes
the origin of the footprint.

> How and why would anyone create parts at 0,0 in the extreme upper
> left corner of a PCB?

Again, elements vs footprints.=C2=A0 A footprint should have a reaso= nable
0,0 point and should be stored with a 0,0 in the Element[] coordinate
slot.

Once on a pcb, it's not a footprint, it's an element, and the
"location" information in the Element[] coordinate slot is used t= o
keep track of its location.

> I am guessing that the origin
> coordinates written to the footprint file, are related to relative
> coordinates based on a local origin and the cursor position.

If you happen to have something other than 0,0 in the footprint file= ,
when you paste that footprint onto the pcb, it will be pasted away
from the crosshair by that amount.=C2=A0 *After* it's pasted, that
coordinate will be updated to be the new location of the element.

That has not been evident in my tests.=C2=A0 I c= annot see/feel any difference.

=C2=A0

> BUT - and this is the kicker - it does not seem to matter if you
> have an non-zero offset in your footprint file.

That would make sense, since the coordinates in the footprint file only have a real meaning after you place it on a pcb.

It's possible to have more than one Element[] in a footprint file, but<= br> we discourage that ;-)

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