OpenKinect and Processing – Can't display Z co-ordinate

Question

I have this code from Daniel Shiffman (below). I am trying to read out the Z co-ordinate. I'm not sure at all in how to do this, so any help would be much appreciated.

AveragePointTracking.pde

// Daniel Shiffman
// Tracking the average location beyond a given depth threshold
// Thanks to Dan O'Sullivan
// http://www.shiffman.net
// https://github.com/shiffman/libfreenect/tree/master/wrappers/java/processing

import org.openkinect.*;
import org.openkinect.processing.*;

// Showing how we can farm all the kinect stuff out to a separate class
KinectTracker tracker;
// Kinect Library object
Kinect kinect;

void setup() {
  size(640,600);
  kinect = new Kinect(this);
  tracker = new KinectTracker();
}

void draw() {
  background(255);

  // Run the tracking analysis
  tracker.track();
  // Show the image
  tracker.display();

  // Let's draw the raw location
  PVector v1 = tracker.getPos();
  fill(50,100,250,200);
  noStroke();
  ellipse(v1.x,v1.y,10,10);

  // Let's draw the "lerped" location
  //PVector v2 = tracker.getLerpedPos();
  //fill(100,250,50,200);
  //noStroke();
  //ellipse(v2.x,v2.y,20,20);

  // Display some info
  int t = tracker.getThreshold();
  fill(0);
  text("Location-X: " + v1.x,10,500);
  text("Location-Y: " + v1.y,10,530);
  text("Location-Z: ",10,560);
  text("threshold: " + t,10,590);
}

void stop() {
  tracker.quit();
  super.stop();
}

KinectTracker.pde

class KinectTracker {

  // Size of kinect image
  int kw = 640;
  int kh = 480;
  int threshold = 500;

  // Raw location
  PVector loc;

  // Interpolated location
  PVector lerpedLoc;

  // Depth data
  int[] depth;


  PImage display;

  KinectTracker() {
    kinect.start();
    kinect.enableDepth(true);

    // We could skip processing the grayscale image for efficiency
    // but this example is just demonstrating everything
    kinect.processDepthImage(true);

    display = createImage(kw,kh,PConstants.RGB);

    loc = new PVector(0,0);
    lerpedLoc = new PVector(0,0);
  }

  void track() {

    // Get the raw depth as array of integers
    depth = kinect.getRawDepth();

    // Being overly cautious here
    if (depth == null) return;

    float sumX = 0;
    float sumY = 0;
    float count = 0;

    for(int x = 0; x < kw; x++) {
      for(int y = 0; y < kh; y++) {
        // Mirroring the image
        int offset = kw-x-1+y*kw;
        // Grabbing the raw depth
        int rawDepth = depth[offset];

        // Testing against threshold
        if (rawDepth < threshold) {
          sumX += x;
          sumY += y;
          count++;
        }
      }
    }
    // As long as we found something
    if (count != 0) {
      loc = new PVector(sumX/count,sumY/count);
    }

    // Interpolating the location, doing it arbitrarily for now
    lerpedLoc.x = PApplet.lerp(lerpedLoc.x, loc.x, 0.3f);
    lerpedLoc.y = PApplet.lerp(lerpedLoc.y, loc.y, 0.3f);
  }

  PVector getLerpedPos() {
    return lerpedLoc;
  }

  PVector getPos() {
    return loc;
  }

  void display() {
    PImage img = kinect.getDepthImage();

    // Being overly cautious here
    if (depth == null || img == null) return;

    // Going to rewrite the depth image to show which pixels are in threshold
    // A lot of this is redundant, but this is just for demonstration purposes
    display.loadPixels();
    for(int x = 0; x < kw; x++) {
      for(int y = 0; y < kh; y++) {
        // mirroring image
        int offset = kw-x-1+y*kw;
        // Raw depth
        int rawDepth = depth[offset];

        int pix = x+y*display.width;
        if (rawDepth < threshold) {
          // A red color instead
          display.pixels[pix] = color(245,100,100);
        } 
        else {
          display.pixels[pix] = img.pixels[offset];
        }
      }
    }
    display.updatePixels();

    // Draw the image
    image(display,0,0);
  }

  void quit() {
    kinect.quit();
  }

  int getThreshold() {
    return threshold;
  }

  void setThreshold(int t) {
    threshold =  t;
  }
}

Answer 1

There are two main steps:

1. fetching the depths (which KinectTracker already does in the track() method)
2. getting the depth for the current pixel using an offset to find a position in a 1D depth array based on a 2D position (x,y) (which again is kind of done in the track() method: int offset = kw-x-1+y*kw;)

Note that the coordinate is mirrored though, usually to the index is computed like so:

index = y*width+x

as explained in the get() reference notes

So in theory all you need to this is something like this at the end of the track() method:

lerpedLoc.z = depth[kw-((int)lerpedLoc.x)-1+((int)lerpedLoc.y)*kw];

like so:

void track() {

    // Get the raw depth as array of integers
    depth = kinect.getRawDepth();

    // Being overly cautious here
    if (depth == null) return;

    float sumX = 0;
    float sumY = 0;
    float count = 0;

    for(int x = 0; x < kw; x++) {
      for(int y = 0; y < kh; y++) {
        // Mirroring the image
        int offset = kw-x-1+y*kw;
        // Grabbing the raw depth
        int rawDepth = depth[offset];

        // Testing against threshold
        if (rawDepth < threshold) {
          sumX += x;
          sumY += y;
          count++;
        }
      }
    }
    // As long as we found something
    if (count != 0) {
      loc = new PVector(sumX/count,sumY/count);
    }

    // Interpolating the location, doing it arbitrarily for now
    lerpedLoc.x = PApplet.lerp(lerpedLoc.x, loc.x, 0.3f);
    lerpedLoc.y = PApplet.lerp(lerpedLoc.y, loc.y, 0.3f);
    lerpedLoc.z = depth[kw-((int)lerpedLoc.x)-1+((int)lerpedLoc.y)*kw];
  }

I can't test with a kinect right now, but this should work. I'm not sure if you'll get the depth for the correct pixel or a mirrored one. The only other option is something like:

lerpedLoc.z = depth[((int)lerpedLoc.x)+((int)lerpedLoc.y)*kw];