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Date:	Fri, 14 Dec 2012 17:28:44 +0100 (CET)
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Subject:	Re: [geda-user] Find rat lines
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On Fri, 14 Dec 2012, Chris Smith wrote:

> On 14/12/2012 13:41, gedau AT igor2 DOT repo DOT hu wrote:
>>
>> In this system your above method is Markus' first touch method and some
>> extra details. With these details it would work better and would not
>> restrict the user to build traces only in one way, but I still have some
>> questions:
>>
>> 1. what happens if I cut an existing, tagged net in a way a segment
>> falls off? Does it become a floating (not associated) net or, does it
>> keep its tag reflecting original user intention?
>
> IMHO, the system should never automatically change an attribute from a
> specific to a more general value -- to do so is effectively throwing
> away information.  The track segment should keep its association; the
> user can manually change it if desired.

Yes, this is one of the approaches. Advantage is simplicity without losing 
info, drawback is more manual tweaking when one doesn't build things 
incrementally but breaks/rewires.

>> 2. What happens if I draw a line accross the board shorting two random
>> nets? I started the line in the middle of nothing, so it would be
>> floating (if starting point matters; causing 2 shorts); or would it be
>> attached to the net of the first line it hits (first touch; only one
>> short, with the second line)?
>>
>> 3. alternative wording of 2.: what happens if I add an object that
>> connects an existing floating net to two existing non-floating nets in
>> the same time?
>
> To be honest I don't think it really matters, as long as it behaves in a
> consistent manner.  I would suggest inheriting the netname of the first
> connected track and marking a short with the second.

Reasonable choice. By the way, a minimal cut solution would highlight 
something very similar in the same situation. The above method would show 
the crossing, a minimal cut would show the extra line causing the short, 
attaching it to whichever net randomly in case 2 or suggesting to cut 
whichever line at the crossing (leaving a rat behind) in case 3.

So beside this method retrains more information about user intention, 
which is good, in many cases it would highlight something very similar to 
a minimal cut.

This argument is relevant only if the final decision needs to consider 
the extra UI/conceptual features put on the user and/or the effort 
required to implement for a developer.


Regards,

Tibor

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