Point Cloud from Kinect using Freenect and Python
<p>I have an XBox 360 Kinect Sensor connected via Linux Mint.  I am trying to create a CSV file where the Z values represent the distance from the sensor-in short, I want to use the Kinect as a short-range 3D scanner.  I have the code below producing a CSV file but the values are quite strange and do not seem to represent the real world XYZ values.  Here is a sample of the resulting CSV file and all rows have similar values.
x,y,z
-0.22424937966362582,0.16117004627017431,-0.39249255932230664
-0.22424937966362582,0.16050597521014062,-0.39249255932230664
-0.22424937966362582,0.15984190415010693,-0.39249255932230664</p>

<p>What do these number mean?  How can I get Z values in meters or centimeters? Where am I going wrong?</p>

<p>Here is an example of the code I am running that was gleaned from this Github page <a href="http://hhttps://github.com/amiller/libfreenect-goodies" rel="nofollow">https://github.com/amiller/libfreenect-goodie</a>s</p>

<p>Here is my Python code.</p>

<pre><code>#!/usr/bin/python

import sys, traceback
import freenect
import cv2
import numpy as np
import csv
print "running"

def get_depth():
    array,_ = freenect.sync_get_depth()
    array = array.astype(np.uint8)
    return array

def depth2xyzuv(depth, u=None, v=None):
    if u is None or v is None:
        u,v = np.mgrid[:480,:640]  
    # Build a 3xN matrix of the d,u,v data
    C = np.vstack((u.flatten(), v.flatten(), depth.flatten(), 0*u.flatten()+1))
    # Project the duv matrix into xyz using xyz_matrix()
    X,Y,Z,W = np.dot(xyz_matrix(),C)
    X,Y,Z = X/W, Y/W, Z/W
    xyz = np.vstack((X,Y,Z)).transpose()
    xyz = xyz[Z&lt;0,:]
    # Project the duv matrix into U,V rgb coordinates using rgb_matrix() and xyz_matrix()
    U,V,_,W = np.dot(np.dot(uv_matrix(), xyz_matrix()),C)
    U,V = U/W, V/W
    uv = np.vstack((U,V)).transpose()
    uv = uv[Z&lt;0,:]
    return xyz
def uv_matrix():
  """Returns a matrix you can use to project XYZ coordinates (in meters) into
      U,V coordinates in the kinect RGB image"""
  rot = np.array([[ 9.99846e-01,   -1.26353e-03,   1.74872e-02], 
                  [-1.4779096e-03, -9.999238e-01,  1.225138e-02],
                  [1.747042e-02,   -1.227534e-02,  -9.99772e-01]])
  trans = np.array([[1.9985e-02, -7.44237e-04,-1.0916736e-02]])
  m = np.hstack((rot, -trans.transpose()))
  m = np.vstack((m, np.array([[0,0,0,1]])))
  KK = np.array([[529.2, 0, 329, 0],
                 [0, 525.6, 267.5, 0],
                 [0, 0, 0, 1],
                 [0, 0, 1, 0]])
  m = np.dot(KK, (m))
  return m
def xyz_matrix():
  fx = 594.21
  fy = 591.04
  a = -0.0030711
  b = 3.3309495
  cx = 339.5
  cy = 242.7
  mat = np.array([[1/fx, 0, 0, -cx/fx],
                  [0, -1/fy, 0, cy/fy],
                  [0,   0, 0,    -1],
                  [0,   0, a,     b]])
  return mat
depth = get_depth()
depthpoints = depth2xyzuv(depth)

print "Create csv header..."
f = open("/home/gerry/depthtest.csv",'a')
f.write("x,y,z\n")
f.close()
print "writing to text file...please wait...."
with open("/home/gerry/depthtest.csv", 'a') as f:
    csvwriter = csv.writer(f)
    csvwriter.writerows(depthpoints)   
print "finished writing to text file..."
print "done"
</code></pre>