Re: [Matplotlib-users] matplotlib.nxutils.pnpoly returns True for some vertexes, and False for others
On Tue, Jan 29, 2013 at 5:55 PM, Maria Liukis liu...@usc.edu wrote: Hello, I tested the following code on my Mac laptop and our production Linux server both running matplotlib V1.0.1. Both machines observe the same output from the code, so I was wondering if somebody is aware of the problem or if it's some undocumented feature of pnpoly() function from matplotlib.nxutils? I use matplotlib.nxutils.pnpoly() function from matplotlib to determine if point belongs to the polygon. The following code: import numpy as np import matplotlib.nxutils as nx coords = np.array([[4.0, 1.0], [4.0, 4.0], [5.0, 5.0], [6.0, 4.0], [5.0, 0.0]]) nx.pnpoly(4.0, 1.0, coords) 1 nx.pnpoly(4.0, 4.0, coords) 1 nx.pnpoly(5.0, 5.0, coords) 0 nx.pnpoly(6.0, 4.0, coords) 0 nx.pnpoly(5.0, 0.0, coords) 0 The question is why first two vertexes are considered to be inside of defined polygon, and last 3 vertexes are not? My guess, it's treating the polygon as a semi-open set, and I wonder if it can be changed to make all vertexes inclusive? Any help would be greatly appreciated. Many thanks, Masha The documentation for pnpoly() for that version states: A point on the boundary may be treated as inside or outside. See `pnpoly http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html`_ Note that in version 1.2.0, the nxutils module was deprecated. pnpoly() and points_inside_poly() are now merely wrappers around the polygon's implementations of point-testing, which differs from the nxutils' implementation, so you may get slightly different results. Do note that the point-testing algorithm in matplotlib was more geared for visualization purposes rather than for strict geometric needs. If you need a more well-behaved point-tester (and faster if the polygon is prepared), use the shapely package instead. I hope that clears things up! Cheers! Ben Root -- Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_jan___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] matplotlib.nxutils.pnpoly returns True for some vertexes, and False for others
Ben, Many thanks! Will try to use shapely package then. Masha liu...@usc.edu On Jan 30, 2013, at 6:59 AM, Benjamin Root wrote: On Tue, Jan 29, 2013 at 5:55 PM, Maria Liukis liu...@usc.edu wrote: Hello, I tested the following code on my Mac laptop and our production Linux server both running matplotlib V1.0.1. Both machines observe the same output from the code, so I was wondering if somebody is aware of the problem or if it's some undocumented feature of pnpoly() function from matplotlib.nxutils? I use matplotlib.nxutils.pnpoly() function from matplotlib to determine if point belongs to the polygon. The following code: import numpy as np import matplotlib.nxutils as nx coords = np.array([[4.0, 1.0], [4.0, 4.0], [5.0, 5.0], [6.0, 4.0], [5.0, 0.0]]) nx.pnpoly(4.0, 1.0, coords) 1 nx.pnpoly(4.0, 4.0, coords) 1 nx.pnpoly(5.0, 5.0, coords) 0 nx.pnpoly(6.0, 4.0, coords) 0 nx.pnpoly(5.0, 0.0, coords) 0 The question is why first two vertexes are considered to be inside of defined polygon, and last 3 vertexes are not? My guess, it's treating the polygon as a semi-open set, and I wonder if it can be changed to make all vertexes inclusive? Any help would be greatly appreciated. Many thanks, Masha The documentation for pnpoly() for that version states: A point on the boundary may be treated as inside or outside. See `pnpoly http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html`_ Note that in version 1.2.0, the nxutils module was deprecated. pnpoly() and points_inside_poly() are now merely wrappers around the polygon's implementations of point-testing, which differs from the nxutils' implementation, so you may get slightly different results. Do note that the point-testing algorithm in matplotlib was more geared for visualization purposes rather than for strict geometric needs. If you need a more well-behaved point-tester (and faster if the polygon is prepared), use the shapely package instead. I hope that clears things up! Cheers! Ben Root -- Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_jan___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
