[Doc] Add Data Structures and Elements (#2070)

* [WIP][Doc] Add Data Structures and Elements

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* Update docs/en/advanced_guides/structures.md

* Update docs/en/advanced_guides/structures.md

Co-authored-by: Miao Zheng <76149310+MeowZheng@users.noreply.github.com>
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MengzhangLI 2022-10-28 22:22:44 +08:00 committed by GitHub
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# Structures
To unify input and output interfaces between different models and modules, OpenMMLab 2.0 MMEngine defines an abstract data structure,
it has implemented basic functions of `Create`, `Read`, `Update`, `Delete`, supported data transferring among different types of devices
and tensor-like or dictionary-like operations such as `.cpu()`, `.cuda()`, `.get()` and `.detach()`.
More details can be found [here](https://github.com/open-mmlab/mmengine/blob/main/docs/en/advanced_tutorials/data_element.md).
MMSegmentation also follows this interface protocol and defines `SegDataSample` which is used to encapsulate the data of semantic segmentation task.
## Semantic Segmentation Data SegDataSample
[SegDataSample](mmseg.structures.SegDataSample) includes three main fields `gt_sem_seg`, `pred_sem_seg` and `seg_logits`, which are used to store the annotation information and prediction results respectively.
| Field | Type | Description |
| -------------- | ------------------------- | ------------------------------------------ |
| gt_sem_seg | [`PixelData`](#pixeldata) | Annotation information. |
| pred_instances | [`PixelData`](#pixeldata) | The predicted result. |
| seg_logits | [`PixelData`](#pixeldata) | The raw (non-normalized) predicted result. |
The following sample code demonstrates the use of `SegDataSample`.
```python
import torch
from mmengine.structures import PixelData
from mmseg.structures import SegDataSample
img_meta = dict(img_shape=(4, 4, 3),
pad_shape=(4, 4, 3))
data_sample = SegDataSample()
# defining gt_segmentations for encapsulate the ground truth data
gt_segmentations = PixelData(metainfo=img_meta)
gt_segmentations.data = torch.randint(0, 2, (1, 4, 4))
# add and process property in SegDataSample
data_sample.gt_sem_seg = gt_segmentations
assert 'gt_sem_seg' in data_sample
assert 'sem_seg' in data_sample.gt_sem_seg
assert 'img_shape' in data_sample.gt_sem_seg.metainfo_keys()
print(data_sample.gt_sem_seg.shape)
'''
(4, 4)
'''
print(data_sample)
'''
<SegDataSample(
META INFORMATION
DATA FIELDS
gt_sem_seg: <PixelData(
META INFORMATION
img_shape: (4, 4, 3)
pad_shape: (4, 4, 3)
DATA FIELDS
data: tensor([[[1, 1, 1, 0],
[1, 0, 1, 1],
[1, 1, 1, 1],
[0, 1, 0, 1]]])
) at 0x1c2b4156460>
) at 0x1c2aae44d60>
'''
# delete and change property in SegDataSample
data_sample = SegDataSample()
gt_segmentations = PixelData(metainfo=img_meta)
gt_segmentations.data = torch.randint(0, 2, (1, 4, 4))
data_sample.gt_sem_seg = gt_segmentations
data_sample.gt_sem_seg.set_metainfo(dict(img_shape=(4,4,9), pad_shape=(4,4,9)))
del data_sample.gt_sem_seg.img_shape
# Tensor-like operations
data_sample = SegDataSample()
gt_segmentations = PixelData(metainfo=img_meta)
gt_segmentations.data = torch.randint(0, 2, (1, 4, 4))
cuda_gt_segmentations = gt_segmentations.cuda()
cuda_gt_segmentations = gt_segmentations.to('cuda:0')
cpu_gt_segmentations = cuda_gt_segmentations.cpu()
cpu_gt_segmentations = cuda_gt_segmentations.to('cpu')
```
## Customize New Property in SegDataSample
If you want to customize new property in `SegDataSample`, you may follow [SegDataSample](https://github.com/open-mmlab/mmsegmentation/blob/1.x/mmseg/structures/seg_data_sample.py) below:
```python
class SegDataSample(BaseDataElement):
...
@property
def xxx_property(self) -> xxxData:
return self._xxx_property
@xxx_property.setter
def xxx_property(self, value: xxxData) -> None:
self.set_field(value, '_xxx_property', dtype=xxxData)
@xxx_property.deleter
def xxx_property(self) -> None:
del self._xxx_property
```
Then a new property would be added to `SegDataSample`.

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@ -16,7 +16,7 @@ class SegDataSample(BaseDataElement):
>>> import torch
>>> import numpy as np
>>> from mmengine.structures import PixelData
>>> from mmseg.core import SegDataSample
>>> from mmseg.structures import SegDataSample
>>> data_sample = SegDataSample()
>>> img_meta = dict(img_shape=(4, 4, 3),