My goal is to overlay a standard UIKit view (for the moment, I'm just creating a UILabel but eventually I'll have custom content) over a detected shape using image tracking and the Vuforia AR SDK. I have something that works, but with a "fudge" term that I cannot account for. I'd like to understand where my error is, so I can either justify the existence of this correction or use a different algorithm that's known to be valid.

My project is based on the ImageTargets sample project in the Vuforia SDK. Where their EAGLView iterates over the results to render the OpenGL teapots, I've replaced this with a call out to my ObjC++ class TrackableObjectController. For each trackable result, it does this:

- (void)augmentedRealityView:(EAGLView *)view foundTrackableResult:(const QCAR::TrackableResult *)trackableResult
{
    // find out where the target is in Core Animation space
    const QCAR::ImageTarget* imageTarget = static_cast<const QCAR::ImageTarget*>(&(trackableResult->getTrackable()));
    TrackableObject *trackable = [self trackableForName: TrackableName(imageTarget)];
    trackable.tracked = YES;
    QCAR::Vec2F size = imageTarget->getSize();
    QCAR::Matrix44F modelViewMatrix = QCAR::Tool::convertPose2GLMatrix(trackableResult->getPose());
    CGFloat ScreenScale = [[UIScreen mainScreen] scale];
    float xscl = qUtils.viewport.sizeX/ScreenScale/2;
    float yscl = qUtils.viewport.sizeY/ScreenScale/2;
    QCAR::Matrix44F projectedTransform = {1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1};
    QCAR::Matrix44F qcarTransform = {1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1};
    /* this sizeFudge constant is here to put the label in the correct place in this demo; I had thought that
     * the problem was related to the units used (I defined the length of the target in mm in the Target Manager;
     * the fact that I've got to multiply by ten here could be indicative of the app int
ios uikit opengl-es-2.0 augmented-reality vuforia
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