Explain code in Kinect SDK - kinect

Question

I am working with Kinect and reading example from DepthWithColor-D3D, has some code but i don't understand yet.
// loop over each row and column of the color
for (LONG y = 0; y < m_colorHeight; ++y)
{
LONG* pDest = (LONG*)((BYTE*)msT.pData + msT.RowPitch * y);
for (LONG x = 0; x < m_colorWidth; ++x)
{
// calculate index into depth array
int depthIndex = x/m_colorToDepthDivisor + y/m_colorToDepthDivisor * m_depthWidth;
// retrieve the depth to color mapping for the current depth pixel
LONG colorInDepthX = m_colorCoordinates[depthIndex * 2];
LONG colorInDepthY = m_colorCoordinates[depthIndex * 2 + 1];
How to calculate the value of colorInDepthX and colorInDepthY as above code?

Answer 1

colorInDepthX and colorInDepthY is a mapping between the depth and color images so that they will align. Because the Kinect's cameras are slightly offset from each other their field of views are not lined up perfectly.
m_colorCoordinates is defined at the top of the file as such:
m_colorCoordinates = new LONG[m_depthWidth*m_depthHeight*2];
This is a single dimension array representing a 2-dimensional image, it is populated just above the code block you post in your question:
// Get of x, y coordinates for color in depth space
// This will allow us to later compensate for the differences in location, angle, etc between the depth and color cameras
m_pNuiSensor->NuiImageGetColorPixelCoordinateFrameFromDepthPixelFrameAtResolution(
cColorResolution,
cDepthResolution,
m_depthWidth*m_depthHeight,
m_depthD16,
m_depthWidth*m_depthHeight*2,
m_colorCoordinates
);
As described in the comment, this is running an calculation provided by the SDK to map the color and depth coordinates onto each other. The result is placed inside of m_colorCoordinates.
colorInDepthX and colorInDepthY are simply values within the m_colorCoordinates array that are being acted upon in the current cycle of the loop. They are not "calculated", per se, but just point to what already exists in m_colorCoordinates.
The function that handles the mapping between color and depth images is explained in the Kinect SDK at MSDN. Here is a direct link:
http://msdn.microsoft.com/en-us/library/jj663856.aspx