Learn how to make your Python code more efficient by using specific algorithms to solve computational problems for data sets in two dimensions or geometric shapes in GUI applications. George Heineman will show you to how to determine whether two polygons intersect.Python tutorial 2019 #27 POLYGONs INTERSECTION ALGORITHM
He'll demonstrate examples in real time, narrating key concepts and steps along the way. By the end of this course, you'll know how to construct and use both simple and convex polygons efficiently.
The Python code is written for Python 3, and you should be sure to use this version to avoid any frustrations in using the code. Intermediate Python: Introduction. There are several algorithms to compute the convex hull for a two-dimensional data set.
You are encouraged to run the sample applications for constructing convex hulls.
Some sample small data sets will be included and used in the presentation. George T. Heineman is an associate professor of computer science at Worcester Polytechnic Institute, with research interests in software engineering.
Aside from his professional pursuits, George is an avid puzzler. He invented Sujiken, a Sudoku variation played on a right triangle arrangement of cells in which numbers cannot repeat in a horizontal row, vertical column, or diagonal in any direction.
He also invented Trexagon, a Ken-Ken variation involving triangles instead of a square arrangement and wrote Trexagon Puzzles: Mathematically Logical. See more at sujiken. The timeframes are only estimates and may vary according to how the class is progressing. George Heineman. What you'll learn Instructor Schedule Learn how to make your Python code more efficient by using specific algorithms to solve computational problems for data sets in two dimensions or geometric shapes in GUI applications.
Use algorithms for computing the convex hull for a data set. Compute the intersection of two convex polygons without relying on complicated third-party Python libraries. This training course is for you because You work with Python and are interested in modeling two-dimensional information You're a programmer with a keen interest in algorithms You are a data scientist looking for additional insights into two-dimensional data sets You want to design and implement dynamic graphical user interfaces.
Prerequisites Knowledge of Python Rudimentary knowledge of polygons and geometrical shapes Install Python 3 The Python code is written for Python 3, and you should be sure to use this version to avoid any frustrations in using the code Install Python 3 The Python code is written for Python 3, and you should be sure to use this version to avoid any frustrations in using the code.
Recommended Preparation: Introduction to Python Intermediate Python: Introduction GitHub Repository There are several algorithms to compute the convex hull for a two-dimensional data set. Activities: Choosing a representation for Polygons Exercise: GUI Application to construct polygons Computing convex hull for two-dimensional data set Exercise: Apply to arbitrary data, using Akl-Toussaint heuristic Brute-force algorithm for computing intersection of two polygons Exercise: Evaluate performance Algorithm for computing intersection of convex polygons Exercise: Evaluate performance.
Sign in.Documentation Help Center. The output arguments, xi and yicontain the x - and y -coordinates of each point at which a segment of the first polyline intersects a segment of the second.
In the case of overlapping, collinear segments, the intersection is actually a line segment rather than a point, and both endpoints are included in xiyi.
The k -th row of ii indicates which polyline segments give rise to the intersection point xi kyi k. To remember how these indices work, just think of segments and vertices as fence sections and posts. In general, letting i and j denote the scalar values comprised by the k -th row of iithe intersection indicated by that row occurs where the i -th segment of the first polyline intersects the j -th segment of the second polyline.
But when an intersection falls precisely on a vertex of the first polyline, then i is the index of that vertex. Likewise with the second polyline and the index j. In the case of an intersection at the i -th vertex of the first line, for example, xi k equals x1 i and yi k equals y1 i. Display the intersection points; note that the point 12, 8 appears twice because of a self-intersection near the end of the first part of the polyline. For a given polyline, the x - and y -coordinate vectors must be the same length.
Line segment indices of intersection points, specified as a numeric vector. A modified version of this example exists on your system. Do you want to open this version instead? Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select:. Select the China site in Chinese or English for best site performance.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have been trying to use shapely to find the intersection of a line and a polygon, but I'm having issues with some floating point numbers. Point 2: point that is the intersection of [ 4. If I replace 4. Downloaded the geos-[version].
Opened the. I think we may conclude that your version of Shapely, and the geos libraries, handle this case differently. Unfortunately the code that accesses the precision model is not available in the C api, and therefore neither in Shapely.
Changing to a higher version of geos might solve your issue, though. It works fine on my machine with shapely 1. Learn more.
Asked 7 years, 2 months ago. Active 7 years, 2 months ago. Viewed 11k times. Point 1: point that would be inside the polygon, or 4. However, the result I receive is: [ 4. LineString [ 3. Does anyone have any ideas for what is going on or what I am missing? Edit: I have tested using shapely version 1. In case anyone is curious as to how I updated the geos version on Windows: Downloaded the geos-[version].
Lisa Lisa 93 1 1 gold badge 1 1 silver badge 6 6 bronze badges.
Thanks unutbu for the picture, it looks better than the one I was about to draw! I found two properties that you can print to see the respective versions: shapely. The latter ought to be of interest. Active Oldest Votes.
Program for Point of Intersection of Two Lines
Okay, sorry for the delay. The one it came packaged with was 3. I'm thinking it's like Mike's response with the only other differenceI can think of being different is the platform. Going to mark this as correct since in the end it seems to be something related to a difference in platforms anyways. I tried using Ubuntu Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Post as a guest Name. Email Required, but never shown.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Skip to content. Permalink Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Branch: master.
Find file Copy path. Cannot retrieve contributors at this time. Raw Blame History. In general assumes that whenever two edges intersect, they intersect in a single point that is not a vertex of exither polygon. Might not handle some really special cases, as described in the above paper. Do so by summing angles with each edge in the convex polygon p. Choose based on which one is "outside" if inhalfplane pe. You signed in with another tab or window. Reload to refresh your session.
It only takes a minute to sign up. I'm looking for an algorithm, a high level solution, or even a library which can help me determine if two polygons intersect, in Python. I have the vertices of the two polygons These are single part polygons without any holes in two different arrays. The polygons are 2D i. I'll like to make an function which will return a boolean indicating whether these two polygons intersect.
Python | Intersection of two lists
The spatial data model is accompanied by a group of natural language relationships between geometric objects — contains, intersects, overlaps, touches, etc. It returns None if they don't intersect.
If they intersect it returns the geometry were both intersect. If you know or are interested in learning R it has some useful spatial packages. I know this is an old question, but I've written a python library for handling collisions between concave and convex polygons, as well as circles.
As an argument you can give a list of polygon. And as a return value you get a list of levels. In the list of levels there are the polygons. Sign up to join this community. The best answers are voted up and rise to the top.
Home Questions Tags Users Unanswered. Finding if two polygons Intersect in Python? Ask Question. Asked 6 years, 1 month ago. Active 9 months ago. Viewed 54k times. Please note that I cannot use arcpyor any arcgis components in this. Can you suggest an algorithm or library for doing this?
Martin Thoma 2 2 silver badges 7 7 bronze badges. Devdatta Tengshe Devdatta Tengshe Active Oldest Votes. You could try shapely. They describe spatial relationships and it work on windows The spatial data model is accompanied by a group of natural language relationships between geometric objects — contains, intersects, overlaps, touches, etc.
Intersection poly2 print intersection. ExportToWkt It returns None if they don't intersect. I would love to use this, but I'm on windows, and on both the systems i've tried, I can't get the python bindings to work. I run into the problem described in this post: gis. It's pretty simple to use, here you go!
Qwerty Qwerty 1 1 bronze badge. Sign up or log in Sign up using Google.Here's a simple-and-stupid approach: on input, discretize your polygons into a bitmap. To intersect, AND the bitmaps together.
To produce output polygons, trace out the jaggy borders of the bitmap and smooth the jaggies using a polygon-approximation algorithm. I don't remember if that link gives the most suitable algorithms, it's just the first Google hit. You might check out one of the tools out there to convert bitmap images to vector representations. Maybe you could call on them without reimplementing the algorithm?
The most complex part would be tracing out the bordersI think. Back in the early 90s I faced something like this problem at work, by the way. I muffed it: I came up with a completely different algorithm that would work on real-number coordinates, but seemed to run into a completely unfixable plethora of degenerate cases in the face of the realities of floating-point and noisy input.
Perhaps with the help of the internet I'd have done better! I don't mind the run time I have a few very small polygonsI can also afford getting an approximation of the polygons' intersection that is, a polygon with less points, but which is still contained in the polygons' intersection.
Intersection of two polygons
But it is really important for me that the algorithm will be simple cheaper testing and preferably short less code. I don't need only a boolean answer to the question of whether the two polygons intersect. Here's an approach based on triangulation that is pretty straightforward to implement and can be made to run in O N 2. BTW, O N 2 is optimal for this problem. Imagine two polygons shaped like pitchfork blades intersecting at right angles.
Each has a number of segments proportional to the number of tines; the number of polygons in the intersection is proportional to the square of the number of tines.
Compare all the triangles from P pairwise with all the triangles from Q to detect intersections. Any pair of intersecting triangles can be broken into smaller triangles each of which is in P, in Q, or in the intersection. Whatever you used in step 1 can be reused to help with this. Only keep triangles that are in the intersection. Compute the neighbors of each triangle, by comparing them pairwise, and build an adjacency graph. This graph will contain one connected subgraph for each polygon in the intersection of P and Q.
For each such subgraph, pick a triangle, walk to the edge, and then walk around the edge, producing the segments bounding the corresponding output polygon. I understand the original poster was looking for a simple solution, but unfortunately there really is no simple solution. It uses an adapted version of the Weiler-Atherton algorithm mentioned above.
Though, this should be very efficient as any transformation to the polygon applies in the very same way to the center of mass and the center-node distances can be computed only once. You could use a Polygon Clipping algorithm to find the intersection between two polygons. However these tend to be complicated algorithms when all of the edge cases are taken into account.
One implementation of polygon clipping that you can use your favorite search engine to look for is Weiler-Atherton. Alan Murta has a complete implementation of a polygon clipper GPC.
Another approach is to first divide each polygon into a set of triangles, which are easier to deal with. Meisters does the trick. This page at McGill does a good job of explaining triangle subdivision. A simple algorithm for polygon intersection 6 Here's a simple-and-stupid approach: on input, discretize your polygons into a bitmap. First, triangulate each polygon. This can be a huge approximation depending on your polygons, but here's one : Compute the center of mass for each polygon.
Compute the min or max or average distance from each point of the polygon to the center of mass.You know what I love about programming? Once you know a little bit, you can Frankenstein your way out of a lot of problems. But it just creates a new layer of the intersected areas. I wanted a list of which specific features were intersecting which other specific features in two separate layers.
The print layers lines are optional to determine which layers are being run through the loop. Start at the bottom with O and work your way up. Now for the loop innards. In this case, we just want QGIS to grab the names of the polygons and add them to their respective lists if they intersect.
This thread explains how to access the attributes where the names of your shapes live. Like Like. Like Liked by 1 person. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account.
Notify me of new comments via email. Notify me of new posts via email. Skip to content Contact Me Table of Contents. Posted on April 16, April 16, by gifguide2code. Problem solved. Stitched together from three scripts online. That will be called W for s in layers. That will be called S if s. Share this: Twitter Facebook Pinterest.
Like this: Like Loading Sounds complicated but interesting. Awww, thanks Bernadette! Parte II Blog 2 Engenheiros.