recently i try to write a basic siamese network, i have finished the ‘training’ part and it works.but now i have a problem ,that is ,how can i get the accuracy.because i can’t get a label from the siamese network, i use contrastive loss and the model output just two vectors and i can only calculate their distance,rather than label.
if there exists a threshold of distance can classify the sample pair  1 or 0, then how can i learn the threshold …or  there exist some methods to get labels?
anybody can help me? ^-^ thanks a lot !!