Re: [Tutor] Python & algorithms (Lang line simplification algorithm)
Okay I'll try. What the main job is to do an algorithm which simples a
line. Algorithm deletes points which are unnecessary accurate according to
tolerance distance user gives.
>> I started by converting the pseudocode I had to python.
Pseudocode:
http://web.cs.sunyit.edu/~poissad/projects/Curve/about_algorithms/lang
1. function lang(PointList[], Tolerance)
2. key=0
3. endP= PointList.length-1
4. do {
5. endP= PointList.length-1
6. if (key+1 != endP) // If there are intermediate points
7. line= new Line( PointList[key], PointList[endP])
8. /* Find the point with the furthest perpendicular distance */
9. maxIndex= key+1
10. maxD= perpendicularDistance(line, PointList[maxIndex])
11. for (i=maxIndex+1; i maxD)
14. maxIndex=i
15. maxD=d
16. if (maxD > Tolerance)
17. endP--;
18. else
19. for (i=key+1; i> Still I have problems with perpendicular distance and creating a line
>> with python.
What I mean by creating a line is what Alan answered "checking
distances/intersections
etc only requires the math model." I need the mathematical model not a
picture/graph. I'll try move forward with Bens suggestion of ‘math’ module
which probably help me with both mathematical line model between two points
and its distance between the intermediate points.
> http://docs.python.org/3/library/math.html#trigonometric-functions>.
Here is a picture of the lang algorithm, where you can see distance of
interest by purple
http://psimpl.sourceforge.net/lang.html.
I'll ask later if I can't get this work.
Cheers!
2014-04-15 3:23 GMT+03:00 Ben Finney :
> Laura Kauria writes:
>
> > Thanks a lot for all the help! I got the courage to start at least..
>
> Congratulations! Courage is a necessary ingredient when starting :-)
>
> Could you please avoid top-posting, and instead use interleaved style
> https://en.wikipedia.org/wiki/Posting_style#Interleaved_style> for
> your replies, so the conversation is in a natural order.
>
> > I started by converting the pseudocode I had to python.
>
> If it's short and simple, please post it here so we can discuss it in
> context.
>
> > Still I have problems with perpendicular distance and creating a line
> > with python.
> > I need to create a line between two points and then check what is the
> > distance between a line and intermediate points which were between lines
> > start and end point. If someone could help me with this? I could not
> > understand can I do this without math library or not?
>
> The ‘math’ module in the standard library has trigonometric functions
> http://docs.python.org/3/library/math.html#trigonometric-functions>.
> If you have co-ordinate data and know how to use trigonometry, then
> those functions will do what you expect.
>
> --
> \“If I melt dry ice, can I swim without getting wet?” —Steven |
> `\Wright |
> _o__) |
> Ben Finney
>
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Re: [Tutor] Python & algorithms (Lang line simplification algorithm)
Hi, sorry I don't know the conventions yet. I'd need to know how to create a line between two points. I don't know after many hours checking, how to convert this pseudocode to python. line = new Line( pointList[startPoint], pointList[endPoint]) I've done point list and indexes already, put don't know how to create the line. Laura 2014-04-14 22:21 GMT+03:00 bob gailer : > On 4/14/2014 11:30 AM, Laura Kauria wrote: > >> Thanks a lot for all the help! I got the courage to start at least.. >> >> Some requests regarding posts. > > 1) put your comments following the relevant text rather than at the top. > 2) delete old (irrelevant) text. > 4) be more clear with your questions. > > I started by converting the pseudocode I had to python. >> > > 3) post your code > > Still I have problems with perpendicular distance and creating a line >> with python. >> I need to create a line between two points >> > what does that mean (apart from the obvious) in terms of your code> > >> and then check what is the distance between a line and intermediate >> points which were between lines start and end point. If someone could help >> me with this? >> I'm a geographer student so all possible library suggestions concerning >> spatial data is also appreciated. >> >> 4) be more clear with your questions. > > I can make guesses about what you want, but that wastes time. > > " distance between a line and intermediate points which were between lines > start and end point" as I read this the answer seems to be zero. ( a point > that is between lines start and end point is on the line). I don't think > you mean that. > > We are here to help. The more you tell us the easier it is for us to help. > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Python & algorithms (Lang line simplification algorithm)
Thanks a lot for all the help! I got the courage to start at least..
I started by converting the pseudocode I had to python.
Still I have problems with perpendicular distance and creating a line with
python.
I need to create a line between two points and then check what is the
distance between a line and intermediate points which were between lines
start and end point. If someone could help me with this? I could not
understand can I do this without math library or not?
I'm a geographer student so all possible library suggestions concerning
spatial data is also appreciated.
Laura
2014-04-06 21:30 GMT+03:00 Danny Yoo :
> Hi Laura,
>
>
> Algorithmic code typically is simple enough that standard language
> features should suffice. I think you might pick up an external
> library to make it easier to visualize graphical output, but the core
> algorithms there appear fairly straightforward.
>
> To get some familiarity with basic Python programming, take a look at
> a tutorial like:
>
> http://www.greenteapress.com/thinkpython/thinkpython.html
>
> and see if you can pick up the basic language features of Python. If
> you have questions with that tutorial, feel free to ask here.
>
>
> It looks like you need enough to work with structured data (classes)
> and the basic data structures (lists, numbers). At least from my
> reading of the "curve simplification" page you pointed us to, I don't
> see anything there that's too bad.
>
> * You'll want a way to represent points. I think a structured value
> would be appropriate. Think classes.
>
> * You'll want to represent a sequence of these points. In Java, you
> can hold that collection with ArrayLists or some other list
> implementation. In Python, there's a generic list data structure that
> serves a similar purpose.
>
>
> For example, in Java, you'd represent structured data with classes,
> and a collection of these with a List:
>
> ///
> class Person {
> private String name;
> public Person(String name) { this.name = name; }
> public void greet() { System.out.println("Hello, my name is " + name);
> }
> }
>
> // Usage:
> Person p = new Person("Laura");
> p.sayHello();
> Person p2 = new Person("Lydia");
> List people = new ArrayList<>();
> people.add(p);
> people.add(p2);
> ///
>
>
> And in Python, you can do an analogous construction:
>
> #
> class Person(object):
> def __init__(self, name):
> self.name = name
> def greet(self):
> print("Hello, my name is " + self.name)
>
> ## Usage
> p = Person("Laura")
> p.sayHello()
> p2 = Person("Lydia")
> people = []
> people.append(p)
> people.append(p2)
> #
>
>
> So there should be a lot of transfer of basic knowledge between what
> you've learned in Java to Python programming. Many of the concepts
> are the same, but the names are just different because of the Tower of
> Babel effect. A basic tutorial of Python will cover these general
> topics.
>
>
> What might be domain-specific here is the visualization part: you'll
> want to make it easy to visually see the output of these graphical
> algorithms. You may want to visualize these points on a graphical
> canvas on screen. You could have your program generate an image file
> like a .png, .gif, or .svg file.
>
> Another approach may be to use a GUI toolkit that opens up a canvas as
> part of the program, where you can then manipulate the canvas. If you
> want to take that approach, you might consider Tkinter, which is a GUI
> library that should come bundled with Python if I'm not mistaken.
> See:
>
> http://effbot.org/tkinterbook/canvas.htm
>
> for a canvas example. So once you have the basic algorithms down, you
> might use a Tkinter canvas to visualize and see that your algorithms
> are doing something reasonable.
>
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[Tutor] Python & algorithms (Lang line simplification algorithm)
Hi all, I'm new with python and have done little coding with Java. At uni I would need to start a coding task with python writing a proper/working code and we don't get much help at school. Can someone help with which kinds of libraries I need to download to start to work with lists consisting coordinates? Here are a pseudocode of the algorithm http://web.cs.sunyit.edu/~poissad/projects/Curve/about_algorithms/lang Thanks for all the answers! Laura ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
