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; iendP; i++)
12. d= perpendicularDistance(line, PointList[i])
13. if (d maxD)
14. maxIndex=i
15. maxD=d
16. if (maxD Tolerance)
17. endP--;
18. else
19. for (i=key+1; iendP; i++)
20. PointList.remove(i)
21. key= endP
22. } while ( endP != PointList.length-1 )
23. end
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.
URL: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 ben+pyt...@benfinney.id.au:
Laura Kauria lacat...@gmail.com 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
URL: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
URL: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)
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 d...@hashcollision.org:
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 ListPerson:
///
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);
ListPerson 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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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 bgai...@gmail.com: 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
[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
