Python polygon get points

How to get list of points inside a polygon in python?

Try this code. poly_coords are the coordinates of your polygon, ‘coord’ is coordinate of point you want to check if it is inside the polygon.

def testP(coord, poly_coords): """ The coordinates should be in the form of list of x and y """ test1 = n.array(poly_coords) test2 = n.vstack((poly_coords[1:], poly_coords[:1])) test = test2-test1 m = test[:,1]/test[:,0] c = test1[:,1]-m*test1[:,0] xval = (coord[1]-c)/m print 'xVal:\t'; print xval print (test1[:,0]-xval)*(test2[:,0]-xval) check = n.where((xval>=coord[0])&((test1[:,0]-xval)*(test2[:,0]-xval)<0))[0] print check print len(check) if len(check)%2==0: return False else: return True 

If you want to make it even faster, take out the part of algo related to polygon, slope and offset and run the rest of code using 'map' function. Something like this:

test1 = n.array( your polygon) test2 = n.vstack((test1[1:], test1[:1])) test = test2-test1 m = test[:,1]/test[:,0] c = test1[:,1]-m*test1[:,0] def testP(coord): """ The coordinates should be in the form of list of x and y """ global test, test1, test2, m,c xval = (coord[1]-c)/m check = n.where((xval>=coord[0])&((test1[:,0]-xval)*(test2[:,0]-xval)<0))[0] if len(check)%2==0: return False else: return True coords = n.array(( your coords in x,y )) map (testP, coords) 

You can remove 'print' commands if you want. This code is made for python 2.7

You can use a numpy matrix like a binary image, which can be used with Opencv for example or other image processing libs, Solution 1 So a matrix which size is L x H where

L=max(x) - min (x) H=max(y) - min (y) 

As entry we have your list of tuple(x,y) you gave above which name is poly for example :

import numpy as np matrix =np.zeros((L,H),dtype=np.int32) # you can use np.uint8 if unsigned x ,y 

So we have now a matrix of Size L x H filled with 0, we put now 1 at polygon points positions

I think you can simple do that

matrix[poly]=1 # which will put 1 at each (x,y) of the list **poly** 

we interpret this as a binary (black/white) image which have a contour drawn on it Assume we want to detect this new contour

import cv2 # opencv import ContoursListe,hierarchy = cv2.findContours(self.thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE) poly2=ContoursListe[0] # we take the first only contour 

Note : poly2 is containing a list of points of your polygon and all points forming it, i mean all points of each vertices of your polygon which is what you need can find useful !! you can use cv2.CHAIN_APPROX_SIMPLE parameter to get poly2 containing only end points of the polygon lines which is lighter and which was our input 🙂 important :the type of poly2 is numpy array ,its shape is (n,1,2) and not (n,2)

Now we draw this contour on this image(matrix) and will fill it too 🙂

now we have a matrix where there is 1 on each points forming and filling the polygon , "thickness=-1" has forced to fill this contour, you can put set thickness = 1 to get only the borders if you want to translate, you can do it by adding parameter offset(xtran,ytrans)

to get the indices of all theses points simply call

list_of_points_indices=numpy.nonzero(matrix) 

Which is smarter is to directly transform your list of points (poly) to a contour format (poly2) and draw it on the matrix

poly2=poly.reshape(-1,1,2).astype(np.int32) 

and draw it on the Matrix matrix

matrix =np.zeros((L,H),dtype=np.int32) cv2.drawContours(matrix,[poly2],-1,(1),thickness=-1) 

And get the list of this points with :

list_of_points_indices=numpy.nonzero(matrix) 

Play with thickness to fill or not the polygon , see solution 1 for more details.

Cherif KAOUA 835

I think drawing the polygon and filling it is a good start, you're going to need something like that anyway and those algorithms are usually fine tuned in C. But don't use a RGB image, use a black/white image, and use numpy.where() to find the pixels where it's 1.

According to this question, the mahotas library has a fill_polygon function that works with numpy arrays.

I'm starting the following code from your function (I would subtract the minx and maxx too) but note that I can't test it at all, I'm not on my dev machine.

import numpy as np import mahotas def render(poly): # removed parameter 'z' xs = [i[0] for i in poly] ys = [i[1] for i in poly] minx, maxx = min(xs), max(xs) miny, maxy = min(ys), max(ys) X = maxx - minx + 1 Y = maxy - miny + 1 newPoly = [(x - minx, y - miny) for (x, y) in poly] grid = np.zeros((X, Y), dtype=np.int8) mahotas.polygon.fill_polygon(newPoly, grid) return [(x + minx, y + miny) for (x, y) in np.where(grid)] 

RemcoGerlich 29536

Building upon RemcoGerlich's answer here's a validated function:

import numpy as np import mahotas def render(poly): """Return polygon as grid of points inside polygon. Input : poly (list of lists) Output : output (list of lists) """ xs, ys = zip(*poly) minx, maxx = min(xs), max(xs) miny, maxy = min(ys), max(ys) newPoly = [(int(x - minx), int(y - miny)) for (x, y) in poly] X = maxx - minx + 1 Y = maxy - miny + 1 grid = np.zeros((X, Y), dtype=np.int8) mahotas.polygon.fill_polygon(newPoly, grid) return [(x + minx, y + miny) for (x, y) in zip(*np.nonzero(grid))] 

poly = [ [0, 0], [0, 10], [10, 10], [10, 0] ] plt.figure(None, (5, 5)) x, y = zip(*render(poly)) plt.scatter(x, y) x, y = zip(*poly) plt.plot(x, y, c="r") plt.show() 

Ulf Aslak 7228

I suggest to use matplotlib contains_points()

from matplotlib.path import Path tupVerts=[(86, 52), (85, 52), (81, 53), (80, 52), (79, 48), (81, 49), (86, 53), (85, 51), (82, 54), (84, 54), (83, 49), (81, 52), (80, 50), (81, 48), (85, 50), (86, 54), (85, 54), (80, 48), (79, 50), (85, 49), (80, 51), (85, 53), (82, 49), (83, 54), (82, 53), (84, 49), (79, 49)] x, y = np.meshgrid(np.arange(300), np.arange(300)) # make a canvas with coordinates x, y = x.flatten(), y.flatten() points = np.vstack((x,y)).T p = Path(tupVerts) # make a polygon grid = p.contains_points(points) mask = grid.reshape(300,300) # now you have a mask with points inside a polygon 

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Getting list of QgsPoint from polygon Layer in PyQGIS

In this moment I need to get all vertex from the polygon which represent the region bound, but I have not find the documentation about how to get it.

1 Answer 1

You need objects for QgsGeometry class. In my example (polygon layer with only one feature):

the next code gets the list points of the polygon layer:

layer = iface.activeLayer() feature = layer.getFeatures().next() polygon = feature.geometry().asPolygon() n = len(polygon[0]) for i in range(n): print polygon[0][i] 

After running the code at the Python Console of QGIS, I got each polygon point as a tuple:

(384465,4.45043e+06) (392424,4.46131e+06) (409514,4.45616e+06) (411269,4.44282e+06) (404480,4.43076e+06) (392541,4.43486e+06) (381773,4.44118e+06) (384465,4.45043e+06) 

Observe that the first and last points are matched.

Editing Note:

I edited my answer based in your comment. Next code uses QgsVectorLayer class constructor.

import os my_path = '/home/zeito/pyqgis_data/polygon8.shp' #this is a Linux path root,name = os.path.split(my_path) name = name[:-4] layer = QgsVectorLayer(my_path, name, 'ogr') #This is my provider: in your code is memory QgsMapLayerRegistry.instance().addMapLayer(layer) feature = layer.getFeatures().next() polygon = feature.geometry().asPolygon() n = len(polygon[0]) for i in range(n): print polygon[0][i] 

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