Merge pull request #3494 from pkulzc/master

Update object detection with internal changes and remove unused BUILD files.

research/object_detection/protos/losses.proto

@@ -38,11 +38,17 @@ message WeightedL2LocalizationLoss {
   optional bool anchorwise_output = 1 [default=false];
 }
 
-// SmoothL1 (Huber) location loss: .5 * x ^ 2 if |x| < 1 else |x| - .5
+// SmoothL1 (Huber) location loss.
+// The smooth L1_loss is defined elementwise as .5 x^2 if |x| <= delta and
+// 0.5 x^2 + delta * (|x|-delta) otherwise, where x is the difference between
+// predictions and target.
 message WeightedSmoothL1LocalizationLoss {
   // DEPRECATED, do not use.
   // Output loss per anchor.
   optional bool anchorwise_output = 1 [default=false];
+
+  // Delta value for huber loss.
+  optional float delta = 2 [default=1.0];
 }
 
 // Intersection over union location loss: 1 - IOU