Augmented reality

hi there.

i want to create an augmented application which on recognizing a 3d hand start showing a ring on the finger

I assume by 3D hand you mean human hand.

There are SDKs like manomotion which offer skeleton view of the hand model in real time i.e. you can write a script which on recognizing the skeleton will place the ring on the Ring finger or the 3rd skeleton finger.
You can use unity, there’s great documentation for it.
One thing about this SDK is that it isn’t open source, hence if I assume that you want to publish it to the stores you’ll need a license.

Alternative :

If you want to go little more technical and open source there’s an SDK called OpenPose. This too gives you same functionalities but little heavy on the device (performance wise ) and there isn’t much nice documentation too.

Also you’ll have to cut the ring in half and then super impose on the finger to develop the sense that the ring is actually on the finger.

thanks can i use super imposition in this case ??

No, you can only detect motion of your hand with depth understanding.
Since you need to detect hand you’ll need these SDKs and then for superimposing other SDK, but I haven’t tried it out.