Solving other problems, help find hidden mistakes

After some more testing, I've realized that there were some major problems I need to fix before proceeding any further:
1) the center point (0, 0) on the canvas has some offset (about 3 pixels) in the browser
2) the (x, y) point of the mouse has not been converted from pixel to 3D coord

To quickly fix the first problem, I borrowed some code from a sample C3D demo:

function findPos(obj) {
 var curleft = curtop = 0;
 if (obj.offsetParent) {
  do {
   curleft += obj.offsetLeft;
   curtop += obj.offsetTop;
  } while (obj = obj.offsetParent);
  return [curleft,curtop];
 }
}

function getXandY( event )
{
 var tempDiv = document.getElementsByTagName('canvas')[0];
 var coords = findPos(tempDiv);
 // determine the correct X, Y
 var X = ( ( event.clientX - coords[0] ) + window.pageXOffset )  - (tempDiv.width / 2.0);
 var Y = (tempDiv.height / 2.0) - ( event.clientY - ( coords[1] - window.pageYOffset ) );

 return [X,Y];
}

As for the second problem, it took a little bit to figure out, but then I've came up with a temporary solution. I simply applied the same idea for getting the width of the far clipping plane, except here, I'm using the distance from position of the camera to the point it is looking at. And with that, I've calculated the ratio of the canvas to the actual space.

var camDist = Math.sqrt(Math.pow(camPos[0] - camLook[0], 2) + Math.pow(camPos[1] - camLook[1], 2) + Math.pow(camPos[2] - camLook[2], 2));
var midSpaceWidth = 2 * (camDist * Math.tan(degreesToRadians(theta));
var ratio = midSpaceWidth / tempDiv.width;
var tempX = ratio * currX;
var tempY = ratio * currY;

Now, this temporary solution only works when the object is at the look at position. So now I need to fix it so it'll work for objects at any position.

While coding this part, Andor and I also found a mistake that might have been causing a lot of problems from before. When we were calculating dz in the beginning, we did this:

var dz = dx / Math.tan(theta);

Mathematically, it seems right, but then we realize that the Math.tan needs to take a radian and not a degree number, so we quickly fixed that by changing it to:

var dz = dx / Math.tan(degreesToRadians(theta));

Luckily we saw this as we were making the pixel to 3D coord conversion, otherwise, we might have been stuck for a long time later on without realizing the problem has been there from the very beginning.