Thank you NalinS

Hi srinu4950,

I think David Beard explained the key points in this thread:

https://developer.vuforia.com/forum/android/i-am-getting-distance-fine-values-cm-millimeters-which-format

The scene units are defined using the width value that you provide to the TMS when creating your trackable. So if you have a target that's 10cm wide and define the trackable width as 10, then your scene unit is equivalent to a cm for that target. If you define the trackable width using another unit, such as pixels, you'll need to determine the conversion between pixels and cm for a given target - which would be pixel_width / 10 in this example

So basically Vuforia has no understanding of Units apart from what you supply to it i.e. TMS units

David also adds:

To get the real-world distance of the device from the target you would need to know the printed size of the target. Then you could find the ratio between the defined width of the target and the printed width of the target and use this as a multiplier for the distance. Note that Vuforia has no way of determining the real-world size of the target it is tracking. A 10 inch-wide target and a 5 inch-wide target might track equally well, and look identical to the tracker when the device is moved so the target fills the screen.

So basically you will need to go through a calibration exercise by 1) tweaking the TMS units and 2) calculating this distance multiplier.

HTH

N

BTW it is worth doing a search on "Units"

Thank you so much . You helped me a lot . One more last question is I have uploaded the 248 pixels width image and my printed image size is 800 pixels . So If I use this method 

            QCAR::Matrix34F pose = result->getPose();

            QCAR::Vec3F position(pose.data[3], pose.data[7], pose.data[11]);

            float distance = sqrt(position.data[0] * position.data[0] +

                                  position.data[1] * position.data[1] +

                                  position.data[2] * position.data[2]);

            NSLog(@"distance: %f", distance);

If you try and add the code for the UI Label directly in RenderFrameQCAR it will not work because it gets called in a background thread.

To make it work you need to wrap the code in a method that can get called onthe main thread by using PerformSelectorOnMainThread.

If you search the forums for this you should find some examples as it has come up before.

Regarding the point on units, see this thread for more info: https://developer.vuforia.com/forum/qcar-api/how-interpret-scene-units

HTH

N