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<html>
<head>
<title>EAGLE Help: RATSNEST</title>
</head>
<body bgcolor=white>
<font face=Helvetica,Arial>
<hr>
<i>EAGLE Help</i>
<h1><center>RATSNEST</center></h1>
<hr>
<dl>
<dt>
<b>Function</b>
<dd>
Calculates the shortest possible airwires and polygons.
<p>
<dt>
<b>Syntax</b>
<dd>
<tt>RATSNEST</tt>
<p>
</dl>
<b>See also</b> <a href=88.htm>SIGNAL</a>,
<a href=61.htm>MOVE</a>,
<a href=71.htm>POLYGON</a>,
<a href=81.htm>RIPUP</a>
<p>
The RATSNEST command assesses all of the airwire connections in order
to achieve the shortest possible paths, for instance, after components
have been moved. After reading a netlist via the
<a href=85.htm>SCRIPT</a>
command, it is also useful to use the RATSNEST command to optimize the
length of airwires.
<p>
The RATSNEST command also calculates all Polygons belonging to a
signal. This is necessary in order to avoid the calculation of
airwires for pads already connected with polygons. All of the calculated
areas are then being displayed in the "real mode". Normally, this
decreases the screen redraw speed. You can switch back to the faster
"outline mode" with the RIPUP command.<br>
The automatic calculation of the polygons can be turned off with
<tt><a href=86.htm>SET</a> POLYGON_RATSNEST OFF;</tt>.
<p>
RATSNEST ignores airwires representing signals which have
their own layer in a multilayer board (e.g. layer $GND for signal
GND), apart from signals connecting smd pads to a supply layer with
a via-hole.
<p>
Note that RATSNEST doesn't mark the board drawing as modified, since the
calculated polygon data (if any) is not stored in the board, and the
recalculated airwires don't really constitute a modification of the drawing.
<p>
<b>Zero length airwires</b>
<p>
If two or more wires of the same signal on different routing layers end
at the same point without being connected through a pad or a via, a
<i>zero length airwire</i> is generated, which will be displayed
as an X-shaped cross in the Unrouted layer. The same applies to smds that
belong to the same signal and are placed on opposite sides of the board.
<p>
Such <i>zero length airwires</i> can be picked up with the
<a href=83.htm>ROUTE</a> command just like ordinary airwires.
They may also be handled by placing a <a href=98.htm>VIA</a>
at that point.
<p>
<b>Making sure everything has been routed</b>
<p>
If there is nothing left to be routed, the RATSNEST command will respond
with the message
<pre>
Ratsnest: Nothing to do!
</pre>
Otherwise, if there are still airwires that have not been routed, the
message
<pre>
Ratsnest: xx airwires.
</pre>
will be displayed, where <tt>xx</tt> gives the number of unrouted airwires.
<hr>
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