Weird dot in middle of Processing Kinect (v2) image

Question

I am trying to adapt Daniel Shiffman's code for a basic Kinect (v2) depth cloud using Processing, but there is always a pixel right in the middle of the screen that won't go anywhere, which is pretty annoying. This is an example of what I mean.

You can see it seems to be right at the front and doesnt move when anything in the field of view moves.

Here is the code that i used to generate the image above, (which is a very stripped down version of what i am trying to do)

// imports for openkinect
import org.openkinect.freenect2.*;
import org.openkinect.processing.*;
import java.nio.FloatBuffer;

// dots size is dot_size*skip
int dot_size = 2;

// step size when iterating through pixel array
int skip = 5; 

// Kinect Library object
Kinect2 kinect2;

// Angle for rotation
float a = 3.1;

void setup() {
  // Rendering in P3D
  size(1500,1000,P3D);

  // start the kinect
  kinect2 = new Kinect2(this);
  kinect2.initDepth();
  kinect2.initDevice();

  smooth(16);
  
  // Black background
  background(0);
  
}

void draw() {
  background(0);
  
  // Translate and rotate
  pushMatrix();
  translate(width/2, height/2,50);
  rotateY(a);
  
  // get current depth information
  int[] depth = kinect2.getRawDepth();
  
  // read depth pixels in kinect window bounds
  for (int x = 0; x < kinect2.depthWidth; x+=skip) {
    for (int y = 0; y < kinect2.depthHeight; y+=skip) {
      
      // compute offset for 1D depth array
      int offset = x + y * kinect2.depthWidth;
      
      // get the depth
      int d = depth[offset];
      
      //calculte the x, y, z camera position based on the depth information
      PVector point = depthToPointCloudPos(x, y, d);
      
      // compute depth modifier for colours and such
      float depth_modifier = map(point.z,1000,2048,255,0);
      
      fill(depth_modifier);
      
      pushMatrix();
      translate(point.x,point.y,point.z);
      circle(0,0,skip*dot_size);
      popMatrix();
    }
  }
   
  popMatrix();
}

//calculte the xyz camera position based on the depth data
PVector depthToPointCloudPos(int x, int y, float depthValue) {
  PVector point = new PVector();
  point.z = (depthValue);// / (1.0f); // Convert from mm to meters
  point.x = (x - CameraParams.cx) * point.z / CameraParams.fx;
  point.y = (y - CameraParams.cy) * point.z / CameraParams.fy;
  return point;
}

Here is the contents of CameraParams.pde to make it easy for someone to replicate:

//camera information based on the Kinect v2 hardware
static class CameraParams {
  static float cx = 254.878f;
  static float cy = 205.395f;
  static float fx = 365.456f;
  static float fy = 365.456f;
  static float k1 = 0.0905474;
  static float k2 = -0.26819;
  static float k3 = 0.0950862;
  static float p1 = 0.0;
  static float p2 = 0.0;
}

Does anyone have any idea where this dot is coming from, and how I can get rid of it?

Answer 1

I managed to fix it, it was a bit of a hacky solution, but it worked.. the pixel seems to be showing up at exactly 0 depth, so I just added the code:

if (d == 0){
    continue;
} 

after it calculated the depth of the current pixel, and that worked fine. I thought I would answer my own question in case anyone else had similar problems.

I know its still lurking in the data though, so if anyone has any idea of the source of the problem, I would still like to know why it is occurring - I am pretty new to the Processing language, so I'm sure there is just something I'm missing.

But for now, at least it is "fixed"!