[Matplotlib-users] paths optimizer

[Ian Thomas]

Hello Al,

The search terms you are looking for are 'polygon clipping' and 'boolean
operations on polygons'.

Matplotlib can clip one polygon with respect to another, there is a simple
example at
http://stackoverflow.com/questions/22612323/clipping-a-triagle-with-a-circle-in-matplotlib

Alternatively, for more flexibility use shapely.  For example:

    from shapely.geometry import Polygon
    a = Polygon([(0, 0), (1.1, 0), (1.1, 1.1), (0, 1.1)])
    b = Polygon([(.9, 0), (2, 0), (2, 1.1), (.9, 1.1)])
    c = Polygon([(.9, .9), (2, .9), (2, 2), (.9, 2)])
    d = a.intersection(b).intersection(c)
    print(d)

which outputs

POLYGON ((0.9 0.9, 0.9 1.1, 1.1 1.1, 1.1 0.9, 0.9 0.9))

i.e. a rectangle from x = 0.9 to 1.1 and y from 0.9 to 1.1.

Ian Thomas


On 12 November 2015 at 03:47, Al Niessner <Al.Niessner at gmx.net> wrote:

>
> I have three paths that each define a bounding box. Lets just say I have
> these three in (x,y) coordinates and all are moveto, lineto, lineto,
> lineto, and closepoly:
>
> 1: (0, 0), (1.1, 0), (1.1, 1.1), (0, 1.1), (0, 0)
> 2: (.9, 0), (2, 0), (2, 1.1), (.9, 1.1), (.9, 0)
> 3: (.9, .9), (2, .9), (2, 2), (.9, 2) (.9, .9)
>
> While my paths have more nodes and are not as cleanly vertical and
> horizontal, it does cover the nature of what I am experiencing.
>
> The first thing to note is that each box has overlap at x = 1 and y = 1
> and all three boxes overlap at (1,1).
>
> What I am looking for is an optimizer that would be smart enough to say
> hey, because of the overlap, we can trim the boxes to:
>
> 1: (0,0) (1,0) (1,1) (0,1) (0,0)
> 2: (1,0) (2,0) (2,1), (1,1), (1,0)
> 3: (1,1) (2,1) (2,2), (1,2), (1,1)
>
> I am not sure that optimizer is the right word to use either. I have
> poked around matplotlib a bit (over many years) and tried searching but
> guessing the search terms is not simple either. Hence, I am asking if
> anyone is aware of matplotlib functionality that will help me do this
> task. Any other tool outside of matplotlib would be just as nice of a
> suggestion. One last bit, it has to work for N paths.
>
> As always, thanks in advance.
>
> --
> Al Niessner
>
> I have never found the companion that was so companionable as solitude.
> - From Walden by Henry David Thoreau
>
> The universe is indifferent, and life is brutal; however, it is man's
> choice of behavior that makes them malevolent rather than benevolent.
>
> Some will fall in love with life and drink it from a fountain
> That is pouring like an avalanche coming down the mountain.
> - From the song Pepper by the Butthole Surfers
>
>
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