update center of base anchor to be half of stride

configs/pascal_voc/ssd300_voc.py

@@ -51,7 +51,7 @@ data = dict(
     workers_per_gpu=2,
     train=dict(
         type='RepeatDataset',
-        times=20,
+        times=10,
         dataset=dict(
             type=dataset_type,
             ann_file=[
@@ -113,7 +113,7 @@ lr_config = dict(
     warmup='linear',
     warmup_iters=500,
     warmup_ratio=1.0 / 3,
-    step=[8, 11])
+    step=[16, 20])
 checkpoint_config = dict(interval=1)
 # yapf:disable
 log_config = dict(
@@ -124,7 +124,7 @@ log_config = dict(
     ])
 # yapf:enable
 # runtime settings
-total_epochs = 12
+total_epochs = 24
 dist_params = dict(backend='nccl')
 log_level = 'INFO'
 work_dir = './work_dirs/ssd300_voc'

configs/pascal_voc/ssd512_voc.py

@@ -51,7 +51,7 @@ data = dict(
     workers_per_gpu=2,
     train=dict(
         type='RepeatDataset',
-        times=20,
+        times=10,
         dataset=dict(
             type=dataset_type,
             ann_file=[
@@ -113,7 +113,7 @@ lr_config = dict(
     warmup='linear',
     warmup_iters=500,
     warmup_ratio=1.0 / 3,
-    step=[8, 11])
+    step=[16, 20])
 checkpoint_config = dict(interval=1)
 # yapf:disable
 log_config = dict(
@@ -124,7 +124,7 @@ log_config = dict(
     ])
 # yapf:enable
 # runtime settings
-total_epochs = 12
+total_epochs = 24
 dist_params = dict(backend='nccl')
 log_level = 'INFO'
 work_dir = './work_dirs/ssd512_voc'

configs/ssd300_coco.py

@@ -51,7 +51,7 @@ data = dict(
     workers_per_gpu=3,
     train=dict(
         type='RepeatDataset',
-        times=10,
+        times=5,
         dataset=dict(
             type=dataset_type,
             ann_file=data_root + 'annotations/instances_train2017.json',
@@ -110,7 +110,7 @@ lr_config = dict(
     warmup='linear',
     warmup_iters=500,
     warmup_ratio=1.0 / 3,
-    step=[8, 11])
+    step=[16, 22])
 checkpoint_config = dict(interval=1)
 # yapf:disable
 log_config = dict(
@@ -121,7 +121,7 @@ log_config = dict(
     ])
 # yapf:enable
 # runtime settings
-total_epochs = 12
+total_epochs = 24
 dist_params = dict(backend='nccl')
 log_level = 'INFO'
 work_dir = './work_dirs/ssd300_coco'

configs/ssd512_coco.py

@@ -51,7 +51,7 @@ data = dict(
     workers_per_gpu=3,
     train=dict(
         type='RepeatDataset',
-        times=10,
+        times=5,
         dataset=dict(
             type=dataset_type,
             ann_file=data_root + 'annotations/instances_train2017.json',
@@ -110,7 +110,7 @@ lr_config = dict(
     warmup='linear',
     warmup_iters=500,
     warmup_ratio=1.0 / 3,
-    step=[8, 11])
+    step=[16, 22])
 checkpoint_config = dict(interval=1)
 # yapf:disable
 log_config = dict(
@@ -121,7 +121,7 @@ log_config = dict(
     ])
 # yapf:enable
 # runtime settings
-total_epochs = 12
+total_epochs = 24
 dist_params = dict(backend='nccl')
 log_level = 'INFO'
 work_dir = './work_dirs/ssd512_coco'

mmdet/core/anchor/anchor_generator.py

@@ -3,11 +3,12 @@ import torch
 
 class AnchorGenerator(object):
 
-    def __init__(self, base_size, scales, ratios, scale_major=True):
+    def __init__(self, base_size, scales, ratios, scale_major=True, ctr=None):
         self.base_size = base_size
         self.scales = torch.Tensor(scales)
         self.ratios = torch.Tensor(ratios)
         self.scale_major = scale_major
+        self.ctr = ctr
         self.base_anchors = self.gen_base_anchors()
 
     @property
@@ -15,13 +16,13 @@ class AnchorGenerator(object):
         return self.base_anchors.size(0)
 
     def gen_base_anchors(self):
-        base_anchor = torch.Tensor(
-            [0, 0, self.base_size - 1, self.base_size - 1])
-
-        w = base_anchor[2] - base_anchor[0] + 1
-        h = base_anchor[3] - base_anchor[1] + 1
-        x_ctr = base_anchor[0] + 0.5 * (w - 1)
-        y_ctr = base_anchor[1] + 0.5 * (h - 1)
+        w = self.base_size
+        h = self.base_size
+        if self.ctr is None:
+            x_ctr = 0.5 * (w - 1)
+            y_ctr = 0.5 * (h - 1)
+        else:
+            x_ctr, y_ctr = self.ctr
 
         h_ratios = torch.sqrt(self.ratios)
         w_ratios = 1 / h_ratios

mmdet/models/single_stage_heads/ssd_head.py

@@ -72,12 +72,14 @@ class SSDHead(nn.Module):
         self.anchor_strides = anchor_strides
         for k in range(len(anchor_strides)):
             base_size = min_sizes[k]
+            stride = anchor_strides[k]
+            ctr = ((stride - 1) / 2., (stride - 1) / 2.)
             scales = [1., np.sqrt(max_sizes[k] / min_sizes[k])]
             ratios = [1.]
             for r in anchor_ratios[k]:
                 ratios += [1 / r, r]  # 4 or 6 ratio
             anchor_generator = AnchorGenerator(
-                base_size, scales, ratios, scale_major=False)
+                base_size, scales, ratios, scale_major=False, ctr=ctr)
             indices = list(range(len(ratios)))
             indices.insert(1, len(indices))
             anchor_generator.base_anchors = torch.index_select(