Mail Archives: geda-user/2015/08/17/17:39:13
--001a11c3781af6337b051d889e05
Content-Type: text/plain; charset=UTF-8
A lot of this doesn't make sense. I'm hearing 2 things.
1) If the 0,0 origin coordinates are an absolute position from the PCB
origin
then wouldn't the component origin be in the upper left corner of the PCB?
But that
doesn't happen when you import schematics to the PCB. 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.
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. How and why would anyone
create parts at 0,0 in the extreme
upper left corner of a PCB? 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 Ctrl-M and create a local origin, then
position the cursor over the cross hairs - then the origin will be captured
and written to the buffer as 0,0. That
is my guess (if I can find some time - I'll test this theory). If you
don't have these things co-incident - then you
will have a non-zero value for the origin - and these numbers represent an
offset.
BUT - and this is the kicker - it does not seem to matter if you have an
non-zero offset in your footprint file.
I found this 0805.fp file in my /usr/local/share/pcb/pcblib-newlib/geda
Element[0x00000000 "Standard SMT resistor, capacitor etc" "" "0805" 0 0
-3150 -3150 0 100 ""]
Which has the origin at 0.0. I don't see any difference when I use this
footprint in my layout or if I use this 805.fp footprint
I referred to in an earlier post.
Element["" "Standard SMT resistor, capacitor etc" "" "0805" 2850.00mil
2600.00mil -31.50mil -31.50mil 0 100 ""]
I can place and work with either footprint. And when I search the packaged
libraries, I am finding some footprints with 0.0 origin
values and some with non-zero/offset values.
Dave
On Mon, Aug 17, 2015 at 9:57 AM, DJ Delorie <dj AT delorie DOT com> wrote:
>
> > My understanding is the origin is located at
> > (2850.00mil,2600.00mil). And the reference designator is positioned
> > at (-31.50mil,-31.50mil) relative to the origin. How does one
> > interpret these (2850.00mil,2600.00mil) numbers for the origin?
>
> The standard library should have (0,0) there, because that coordinate
> in the Element[] field is its location relative to the PCB itself.
> (If ome of them doesn't, it may affect where the element is placed
> when you manually place it.)
>
> I.e. that element is at (2850.00mil,2600.00mil) *on the pcb*.
>
> Thus, pcb will position that element such that its mark falls on
> (2850.00mil,2600.00mil).
>
--001a11c3781af6337b051d889e05
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div><div><div><div><div><div><div><div><div><div><br>A lo=
t of this doesn't make sense. I'm hearing 2 things. <br></div></div=
></div><br>1) If the 0,0 origin coordinates are an absolute position from t=
he PCB origin<br></div></div>then wouldn't the component origin be in t=
he upper left corner of the PCB? But that<br></div>doesn't happen when =
you import schematics to the PCB.=C2=A0 The diamond shape origin is <br>in =
the center of this 805 component - no matter where this component is random=
ly placed <br></div>onto the PCB grid.=C2=A0 The component origin cannot be=
linked to absolute PCB coordinates. <br><br></div><div>2) I thought I hear=
d that the origin written to the footprint file, happens to be the absolute=
position <br>of the cursor when captured into the buffer.=C2=A0 How and wh=
y would anyone create parts at 0,0 in the extreme <br>upper left corner of =
a PCB?=C2=A0 I am guessing that the origin coordinates written to the footp=
rint file, are related to <br>relative coordinates based on a local origin =
and the cursor position.=C2=A0 If you Ctrl-M and create a local origin, the=
n <br>position the cursor over the cross hairs - then the origin will be ca=
ptured and written to the buffer as 0,0.=C2=A0 That <br>is my guess (if I c=
an find some time - I'll test this theory).=C2=A0 If you don't have=
these things co-incident - then you <br>will have a non-zero value for the=
origin - and these numbers represent an offset.=C2=A0 <br><br>BUT - and th=
is is the kicker -=C2=A0 it does not seem to matter if you have an non-zero=
offset in your footprint file.<br></div><div><br>I found this 0805.fp file=
in my /usr/local/share/pcb/pcblib-newlib/geda<br></div><br>Element[0x00000=
000 "Standard SMT resistor, capacitor etc" "" "080=
5" 0 0 -3150 -3150 0 100 ""]<br><br></div>Which has the orig=
in at 0.0.=C2=A0 I don't see any difference when I use this footprint i=
n my layout or if I use this 805.fp footprint <br></div><div>I referred to =
in an earlier post.<br></div><div><br>Element["" "Standard S=
MT resistor, capacitor etc" "" "0805" 2850.00mil 2=
600.00mil -31.50mil -31.50mil 0 100 ""]<br><br></div><div>I can p=
lace and work with either footprint. And when I search the packaged librari=
es, I am finding some footprints with 0.0 origin<br></div><div>values and s=
ome with non-zero/offset values.=C2=A0 </div><div><br></div><div>Dave<br></=
div> </div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Mon=
, Aug 17, 2015 at 9:57 AM, DJ Delorie <span dir=3D"ltr"><<a href=3D"mail=
to:dj AT delorie DOT com" target=3D"_blank">dj AT delorie DOT com</a>></span> wrote:<b=
r><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:=
1px #ccc solid;padding-left:1ex"><span class=3D""><br>
> My understanding is the origin is located at<br>
> (2850.00mil,2600.00mil).=C2=A0 And the reference designator is positio=
ned<br>
> at (-31.50mil,-31.50mil) relative to the origin.=C2=A0 How does one<br=
>
> interpret these (2850.00mil,2600.00mil) numbers for the origin?<br>
<br>
</span>The standard library should have (0,0) there, because that coordinat=
e<br>
in the Element[] field is its location relative to the PCB itself.<br>
(If ome of them doesn't, it may affect where the element is placed<br>
when you manually place it.)<br>
<br>
I.e. that element is at (2850.00mil,2600.00mil) *on the pcb*.<br>
<br>
Thus, pcb will position that element such that its mark falls on<br>
(2850.00mil,2600.00mil).<br>
</blockquote></div><br></div>
--001a11c3781af6337b051d889e05--
- Raw text -