PVector, ArrayList, fiddle...

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bustup

PVector, ArrayList, fiddle...

in Programming Questions • 3 years ago

Hey,

sorry for the topic, but I couldn't figure out how to ask this in short words.

I have an ArrayList with a bunch of PVectors in it. And whenever a new Blob appears (Blob detection) I want to add this to the ArrayList, but only if the blob doesn't intersect with a radius of 20 pixels with a PVector in that ArrayList.

Can anyone hint me in the right direction with some pseudo code? Would appreciate it greatly!

Best,

Jonas

Replies(12)

pixelnerve

Re: PVector, ArrayList, fiddle...

3 years ago

blobs might not be completely round, but assuming they are, compute the distance from their centroids.
If that distance is the greater than (blob1.radius+blob2.radius)+20, add it to the array, else don't.
other way could be to generate bouding circles for each blob and do the calculations i just told you about using the BC instead.

kevin.bjo..

Re: PVector, ArrayList, fiddle...

3 years ago

If the radius "r" you are testing is fixed (20), you can get a slight speed increse by using the dot() method, because for any given PVector d, d.mag() is equal to sqrt(d.dot(d)) -- so test against r squared -- that is, 400.0. Will save a fair number of relatively-expensive sqrt's

kb, http://www.riftgame.com/

niteshade

Re: PVector, ArrayList, fiddle...

3 years ago

PVector has a dist() method... so maybe something like this? Might not be the most elegant code, but hopefully gets you started.

ArrayList al;
float x = blobCentroidX;
float y = blobCentroidY;
PVector blobCentroid = new PVector(blobCentroidX, blobCentroidY);
boolean add2Array = true;
for (int i = 0; i < al.size(); i++) {
if (al[i].dist(blobCentroid) < 20) {
add2Array = false;
}
}
if (add2Array == true) {
// add to array
}

bustup

Re: PVector, ArrayList, fiddle...

3 years ago

Yup you're both right, but if I do this with a for-loop, it only checks the current one, not the rest, so lets say I have 6 PVectors in the ArrayList and 7 blobs in an array.

setup() {
canape = new ArrayList<PVector>();
}
draw() {
... lots of code
Blob[] blobs = opencv.blobs(...);
for (int i = 0; i < canapes.size(); i++) {
Canape c = canapes.get(i);
// lets presume i'm looking at canape 4
for (int j = 0; i < blobs.length; i++) {
// and here lets presume i'm looking at blob 7 which isn't in the arraylist
if (sqrt(pow(c.x - blobs[j].centeroid.x, 2) + pow(c.y - blobs[j].centeroid.y, 2)) > 20) {
// add to arraylist
}
}
}
}

The code isn't the one I'm running, but close to it, same principle.

But the thing is, when I check weather or not the blob is on top of another canape, it only checks if I'm on top of canape 4, and if i'm not add it to the ArrayList - it does not check weather or not I'm on top of canape 1, 2, 3, 5 or 6.

Kinda hard to explain, but maybe I'm just not looking at it in the right way.

@kevin.bjorke I'm not that good with PVectors, could you explain how that would work in my code?

Thanks!

bustup

Re: PVector, ArrayList, fiddle...

3 years ago

@niteshade Ah, you replied while I was typing, but your snippet of code assume I only have one blob, not an entire array of blobs I need to check against. But I know how the dist method works not at least.

pixelnerve

Re: PVector, ArrayList, fiddle...

3 years ago

you will need a list of flags that you set as true during your tests. in the end you can check how many canapes your new blob interesects with and do something about it.

bustup

Re: PVector, ArrayList, fiddle...

3 years ago

So I make a class that extends PVector and create a boolean that I set to true if it intersects with another blob? How would that work?

kevin.bjo..

Re: PVector, ArrayList, fiddle...

3 years ago

something like (accuming your Canape "c" has a PVector member "position" rather than its own .x and .y -- re-factor as you like)

PVector d = PVector.sub(c.position,blobs[j].centeroid.x);
float distSq = d.dot(d);

kb, http://www.riftgame.com/

pixelnerve

Re: PVector, ArrayList, fiddle...

3 years ago

im not sure what you mean exactly.
if said you wanted to add blobs to a list if they do not intersect any of the other blobs in the list right?

so here's the deal

boolean[] blobflags = new boolean[blobs.length];
for( every blobflags ) blobflags[i] = false;
for( blob i )
{
boolean flag = false;
for( canape j )
{
float dist = compute_distance_from_canape_to_blob();
// test if the blob intersects with any canape
if( dist < (blobRadius+canapeRadius)+20 )
flag = true;
}
// this means the blob dit not intersect with any in the canape list, so add to list
if( flag == true ) blobflags[i] = true;
// and move on untl you checked every blob against the list
}
// at this point you a a flag list telling you which ones should be added to the list.. just add them.

i did not added the blob at the distance check as i did not want to check the incoming blobs against themselves..

kevin.bjo..

Re: PVector, ArrayList, fiddle...

3 years ago

I was only suggesting a faster alternative to dist()

kb, http://www.riftgame.com/

pixelnerve

Re: PVector, ArrayList, fiddle...

3 years ago

i was wondering about the original poster=)

bustup

Re: PVector, ArrayList, fiddle...

3 years ago

Thanks guys, problem solved! Seems more obvious now after a weekend of sleep.

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