Package: cglacet-smartquadtree
A quadtree is a tree data structure in which each node has exactly four
children. It is a particularly efficient way to store elements when you
need to quickly find them according to their x-y coordinates.A common problem with elements in quadtrees is to detect pairs of
elements which are closer than a definite threshold.The proposed implementation efficiently addresses this problem.fromsmartquadtreeimportQuadtreeCreation & insertion of elementsAs you instantiate your quadtree, you must specify the center of your
space then the height and width.q=Quadtree(0,0,10,10)The output of a quadtree on the console is pretty explicit. (You can
refer to next section for the meaning of “No mask set”)q<smartquadtree.Quadtree at 0x7fc28b93d300>
Total number of elements: 0
No mask setYou can easily insert elements from which you can naturally infer x-y
coordinates (e.g. tuples or lists)q.insert((1,2))q.insert((-3,4))q<smartquadtree.Quadtree at 0x7fc28b93d300>
Total number of elements: 2
No mask set
First elements:
    (1, 2),
    (-3, 4),No error is raised if the element you are trying to insert is outside
the scope of the quadtree. But it won’t be stored anyway!q.insert((-20,0))q<smartquadtree.Quadtree at 0x7fc28b93d300>
Total number of elements: 2
No mask set
First elements:
    (1, 2),
    (-3, 4),If you want to insert other Python objects, be sure to provideget_x()andget_y()methods to your class!classPoint(object):def__init__(self,x,y,color):self.x=xself.y=yself.color=colordef__repr__(self):return"(%.2f,%.2f)%s"%(self.x,self.y,self.color)defget_x(self):returnself.xdefget_y(self):returnself.yYou cannot insert elements of a different type from the first element
inserted.q.insert(Point(2,-7,"red"))But feel free to create a new one and play with it:point_quadtree=Quadtree(5,5,5,5)point_quadtree.insert(Point(2,7,"red"))point_quadtree<smartquadtree.Quadtree at 0x7fc289797a00>
Total number of elements: 1
No mask set
First elements:
    (2.00, 7.00) red,Simple iterationfromrandomimportrandomq=Quadtree(0,0,10,10,16)forainrange(50):q.insert([random()*20-10,random()*20-10])Theprintfunction does not display all elements and uses the__repr__()method of each element.print(q)<smartquadtree.Quadtree at 0x7fc28b94c0b0>
Total number of elements: 50
No mask set
First elements:
    [5.576253335483335, 2.9926458306078647],
    [2.956289387002718, 3.792134207741281],
    [3.9903269308895766, 5.492168007874362],
    ...We can write our own iterator and print each element we encounter the
way we like.from__future__importprint_functionforpinq.elements():print("[%.2f,%.2f]"%(p[0],p[1]),end=" ")[5.58, 2.99] [2.96, 3.79] [3.99, 5.49] [3.43, 1.10] [7.73, 4.09] [9.67, 6.81] [2.95, 4.12] [0.14, 5.80] [2.77, 7.87] [0.05, 1.61] [-8.74, 7.64] [-1.22, 1.90] [-0.95, 3.91] [-3.17, 1.09] [-7.41, 4.26] [-8.25, 6.47] [-6.91, 3.80] [-3.73, 3.10] [-5.74, 8.80] [8.50, -9.31] [2.49, -9.10] [6.64, -8.61] [0.40, -2.93] [7.99, -4.08] [4.71, -6.75] [0.12, -1.84] [0.72, -2.94] [9.62, -9.90] [0.15, -9.75] [8.67, -7.19] [2.44, -3.60] [5.08, -8.63] [8.86, -1.87] [1.07, -9.43] [-7.96, -5.53] [-2.53, -5.75] [-1.31, -5.81] [-7.24, -3.55] [-8.76, -9.37] [-8.48, -1.33] [-1.28, -0.69] [-6.60, -4.65] [-4.28, -0.89] [-7.56, -7.31] [-4.72, -7.02] [-1.98, -2.33] [-3.43, -5.74] [-3.71, -1.13] [-1.01, -7.29] [-2.04, -5.90]It is easy to filter the iteration process and apply the function only
on elements inside a given polygon. Use theset_mask()method and
pass a list of x-y coordinates. The polygon will be automatically
closed.q.set_mask([(-3,-7),(-3,7),(3,7),(3,-7)])print(q)<smartquadtree.Quadtree at 0x7fc28b94c0b0>
Total number of elements: 50
Total number of elements inside mask: 15
First elements inside the mask:
    [2.956289387002718, 3.792134207741281],
    [2.945472950394006, 4.1166899654293765],
    [0.14379102547949074, 5.797490949080599],
    ...The same approach can be used to count the number of elements inside the
quadtree.print(sum(1forxinq.elements()))print(sum(1forxinq.elements(ignore_mask=True)))15
50As a mask is set on the quadtree, we only counted the elements inside
the mask. You can use thesize()method to count elements and ignore
the mask by default. Disabling the mask withset_mask(None)is also
a possibility.print("%delements (size method)"%q.size())print("%delements (don't ignore the mask)"%q.size(False))q.set_mask(None)print("%delements (disable the mask)"%q.size())50 elements (size method)
15 elements (don't ignore the mask)
50 elements (disable the mask)Playing with plots%matplotlibinlinefrommatplotlibimportpyplotaspltq=Quadtree(5,5,5,5,10)forainrange(200):q.insert([random()*10,random()*10])fig=plt.figure()plt.axis([0,10,0,10])q.set_mask(None)forpinq.elements():plt.plot([p[0]],[p[1]],'o',color='lightgrey')q.set_mask([(3,3),(3,7),(7,7),(7,3)])forpinq.elements():plt.plot([p[0]],[p[1]],'ro')_=plt.plot([3,3,7,7,3],[3,7,7,3,3],'r')Iteration on pairs of neighbouring elementsIterating on pairs of neighbouring elements is possible through theneighbour_elements()function. It works as a generator and yields
pair of elements, the first one being inside the mask (if specified),
the second one being in the same cell or in any neighbouring cell, also
in the mask.Note that if(a, b)is yielded byneighbour_elements(),(b, a)will be omitted from future yields.q=Quadtree(5,5,5,5,10)q.set_limitation(2)# do not create a new subdivision if one side of the cell is below 2forainrange(200):q.insert([random()*10,random()*10])fig=plt.figure()plt.axis([0,10,0,10])forpinq.elements():plt.plot([p[0]],[p[1]],'o',color='lightgrey')q.set_mask([(1,1),(4,1),(5,4),(2,5),(1,1)])forpinq.elements():plt.plot([p[0]],[p[1]],'o',color='green')forp1,p2inq.neighbour_elements():if((p1[0]-p2[0])**2+(p1[1]-p2[1])**2<1):plt.plot([p1[0]],[p1[1]],'o',color='red')plt.plot([p2[0]],[p2[1]],'o',color='red')plt.plot([p1[0],p2[0]],[p1[1],p2[1]],'red')_=plt.plot([1,4,5,2,1],[1,1,4,5,1],'r')