Sorting points in an arraylist clockwise

leonidasarch

Hello,

I have an arraylist that contains a number of points that all belong to the edge of an open surface. I am trying to sort the list so that the points are in clockwise order. I have the center c and the normal n of the surface, but still I have no idea of how to do the sorting in terms of code. Any help would be much appreciated!

Chrisir

in theory make a class PointInCircle that holds the PVector and the angle

put this class PointInCircle in an arraylist

now calc each angle using atan2 or so

then make compare method in the class iirc and sort it by angle

gotoloop has written a lot about it

Chrisir

google the keywords here in the forum

leonidasarch

I have the comparison of angles already. Any idea of how to do the sorting afterwards? I've seen examples in stack overflow but I don't understand the syntax

Chrisir

Ask @gotoloop

Or google "sort" here in the forum

Or click on the tag sort

leonidasarch

Ok, thanks a lot for the reply!

quark

Have you created a class that holds the point and the angle about the centre as suggested by chrisir?

The way to sort the points depends on whether you have created a class or not. If you have a class then you can use Java's built in sort routines if not you are going to have to code your own sorting algorithm.

_vk

https://forum.processing.org/one/topic/altenratives-sorting-via-comparable.html

Chrisir

this is for finding you angle (0 degrees is to the right (east))

code by the forum

// angle 

void setup()
{
  size(400, 400);   // always first line
  rectMode(CENTER);
  noStroke();
}


void draw()
{
  background(255); // white

  // atan2 returns the angle (in radians) 
  // from a specified point to the coordinate origin 
  // as measured from the positive x-axis
  float ang = atan2(mouseY-height*0.5, mouseX-width*0.5);


  // ---------------------------------------------------
  // using angle2 here 

  float angle2=ang;  
  if (angle2 < 0) 
    angle2 += TWO_PI;

  // text 
  fill(0); // black 
  text(degrees(angle2), 19, 19);

  // -------------------------------------------------
  // using ang here again  

  // and the rotating bar
  translate(width*0.5, height*0.5);
  rotate(ang);

  fill(200); // gray
  rect(0, 0, width*0.5, height*0.25);

  fill(255, 0, 0); // red 
  rect(width*0.16, 0, width*0.18, height*0.01);
}

leonidasarch

Thanks everyone for the reply! I figured it out eventually :)

Chrisir

Can you post it

leonidasarch

Ok, there you go. I did it in a different way eventually

`
boolean isNeighbour; Particle pt0 = (Particle) arrayOfSideParticles.get(0); pt0.isChecked = true; arrayOfSortedEdgePoints.add(pt0); Particle selected = null;

for (int j=0; j<pt0.linkedParticles.size (); j++) {
  Particle ptB = (Particle) pt0.linkedParticles.get(j);

  if (ptB.isBorder == true) {
    selected = ptB;
    ptB.isChecked = true;
    arrayOfSortedEdgePoints.add(ptB);
    break;
  }
}

while (true) {
  for (int i=0; i<arrayOfSideParticles.size (); i++) {
    Particle pt = (Particle) arrayOfSideParticles.get(i);
    if (selected != null) {
      if (pt.isChecked == false && selected.linkedParticles.contains(pt)) {
        arrayOfSortedEdgePoints.add(pt);
        selected = pt;
        selected.isChecked = true;
      }
    }
  }

  boolean isAllChecked = true;
  for (int i=0; i<arrayOfSideParticles.size (); i++) {
    Particle pt = (Particle) arrayOfSideParticles.get(i);
    if (pt.isChecked == false) {
      isAllChecked = false;
    }
  }
  if (isAllChecked) break;
}`

Chrisir

Thanks!