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Re: Converting Text File To Rectangles

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On 2/13/2013 12:06 PM, Gene Wirchenko wrote:
> On Mon, 11 Feb 2013 21:02:47 -0500, Eric Sosman
> <esosman@comcast-dot-net.invalid> wrote:
>
>> On 2/11/2013 8:51 PM, Scyth3 wrote:
>>> I have a save and load method for certain rectangles I need for a game. Say the user wants to save a map. The outputted map would look like this:
>>>
>>>
>>> 50 250 50 50
>>> 50 350 50 50
>>> 50 400 50 50
>>> 50 500 50 50
>>> 150 300 50 50
>>> 200 450 50 50
>>> 200 500 50 50
>>> 250 150 50 50
>>> 300 100 50 50
>>> 400 50 50 50
>>> 450 150 50 50
>>> 550 100 50 50
>>>
>>> X Y Width Height
>>>
>>> Now, how would I read this, and turn it into a rectangle?
>>
>>      Turning it into twelve rectangles would be easy, but I don't
>> know how you'd turn it into one.  Perhaps you could keep track of
>> the minimum X,Y and the maximum implied X,Y and form one rectangle
>> that surrounds the entire thing.  That rectangle might not be the
>> minimal surrounding rectangle, but it would be minimal among those
>> whose sides were parallel to the axes.
>
>       It would be a minimal regardless of whether the sides were
> parallel to the axes.  The vertices of each rectangle give the
> furthest extent of the rectangle in one direction (or two in the
> parallel case).

     The minimal surrounding rectangle's sides are not necessarily
parallel to the axes.  Counterexample: Let there be two surrounded
rectangles, each a 2x2 square, one centered at (1,1) and the other
at (99,99).  The minimal axis-aligned surrounding rectangle is a
square with one corner at the origin and its opposite at (100,100);
its area is 100*100=10000 and its perimeter is 4*100=400.

     Now consider a long skinny rectangle at a 45-degree angle,
lying athwart the y=x line.  To enclose the two small squares, it
must be 2*sqrt(2) wide and 100*sqrt(2) long, for an area of
2*100*2=400 and a perimeter of 2*(2+100)*sqrt(2)~=288.5, both
considerably smaller than their counterparts on the large square.

     It's true I didn't specify what I meant by "minimal," and
there may be other measures than area and perimeter that would
lead to a different conclusion.  But for those two, at least,
requiring the rectangle's sides to be axis-parallel can lead
to rejecting smaller non-aligned rectangles.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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Converting Text File To Rectangles Scyth3 <zfollette@gmail.com> - 2013-02-11 17:51 -0800
  Re: Converting Text File To Rectangles Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-02-11 21:02 -0500
    Re: Converting Text File To Rectangles Gene Wirchenko <genew@telus.net> - 2013-02-13 09:06 -0800
      Re: Converting Text File To Rectangles Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-02-13 13:25 -0500
        Re: Converting Text File To Rectangles "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-02-15 15:25 +0000
          Re: Converting Text File To Rectangles "John B. Matthews" <nospam@nospam.invalid> - 2013-02-16 13:37 -0500
            [OT] Re: Converting Text File To Rectangles Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-02-16 15:16 -0500
              Re: [OT] Re: Converting Text File To Rectangles "John B. Matthews" <nospam@nospam.invalid> - 2013-02-17 14:16 -0500
        Re: Converting Text File To Rectangles Gene Wirchenko <genew@telus.net> - 2013-02-15 13:09 -0800
  Re: Converting Text File To Rectangles Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-02-12 04:47 -0400
    Re: Converting Text File To Rectangles lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-02-12 12:14 +0000
  Re: Converting Text File To Rectangles lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-02-12 09:47 +0000
    Re: Converting Text File To Rectangles lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-02-12 09:50 +0000
    Re: Converting Text File To Rectangles Roedy Green <see_website@mindprod.com.invalid> - 2013-02-12 18:23 -0800
  Re: Converting Text File To Rectangles Roedy Green <see_website@mindprod.com.invalid> - 2013-02-12 11:41 -0800

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