The SSDMatcher class extends the standard Matcher used by FasterRCNN and it is responsible for matching the default boxes to the ground truth. After estimating the IoUs of all combinations, we use the matcher to find for each default box the best candidate ground truth with overlap higher than the IoU threshold. The SSD version of the matcher has an extra step to ensure that each ground truth is matched with the default box that has the highest overlap. The results of the matcher are used in the loss estimation during the training process of the model.