Depth / Ranged Image to Point Cloud - image

Question

I am trying to create a pointcloud from a depth image / ranged image / displacement map (grey values which correspond to z depth).
Here is the depth image of an trailer vehicle:
http://de.tinypic.com/r/rlvp80/8
Camera Parameters, no rotation: x,y,z: 0,25,0
I get this pointcloud with a aslope ground plane, which should be even (just a quad at 0,0,0 with no rotation):
rotated:
http://de.tinypic.com/r/2mnglj6/8
Here is my code, I try to do this:
normalizedCameraRay = normalize(CameraRay);
Point_in_3D = zDepthValueOfPixelXY /normalizedCameraRay.zValue; //zValue is <= 1
This doesnt seem to work. If I use zDepthValueOfPixelXY * normalizedCameraRay, I got Radial Disortion (everything looks a bit like a sphere).
Any Ideas how to fix this? I attached my code.
Thank you for your ideas
float startPositionX = -((float)image.rows)/2;
float startPositionY = -((float)image.cols)/2;
glm::vec3 cameraWorldPosition(x,y,z);
qDebug() << x << "," << y << ", " << z;
for(int a = 0; a < image.rows;a++)
{
for(int b = 0; b < image.cols;b++)
{
float movementX = startPositionX+b;
float movementY = startPositionY+a;
glm::vec3 ray(movementX, movementY, focal_length);
ray = glm::normalize(ray);
float rayFactor = ((float)image.at<u_int16_t>(a,b)) / ray[2];
glm::vec3 completeRay = rayFactor*ray;
pointCloud[a][b] = completeRay;
/*
ray = completeRay - cameraWorldPosition;
ray = glm::normalize(ray);
rayFactor = ((float)image.at<u_int16_t>(a,b)) / ray[2];
ray = rayFactor * ray;
pointCloud[a][b] = ray;*/
/*
ray = glm::vec3(startPositionX+b,startPositionY-a, image.at<u_int16_t>(a,b));
pointCloud[a][b] = ray;
*/
}
}