## Installation

### Requirements

- Linux (Windows is not officially supported)
- Python 3.5+ (Python 2 is not supported)
- PyTorch 1.1 or higher
- CUDA 9.0 or higher
- NCCL 2
- GCC 4.9 or higher
- [mmcv](https://github.com/open-mmlab/mmcv)

We have tested the following versions of OS and softwares:

- OS: Ubuntu 16.04/18.04 and CentOS 7.2
- CUDA: 9.0/9.2/10.0
- NCCL: 2.1.15/2.2.13/2.3.7/2.4.2
- GCC: 4.9/5.3/5.4/7.3

### Install mmdetection

a. Create a conda virtual environment and activate it.

```shell
conda create -n open-mmlab python=3.7 -y
conda activate open-mmlab
```

b. Install PyTorch stable or nightly and torchvision following the [official instructions](https://pytorch.org/), e.g.,

```shell
conda install pytorch torchvision -c pytorch
```

c. Clone the mmdetection repository.

```shell
git clone https://github.com/open-mmlab/mmdetection.git
cd mmdetection
```

d. Install mmdetection (other dependencies will be installed automatically).

```shell
python setup.py develop
# or "pip install -v -e ."
```

Note:

1. The git commit id will be written to the version number with step d, e.g. 0.6.0+2e7045c. The version will also be saved in trained models.
It is recommended that you run step d each time you pull some updates from github. If C/CUDA codes are modified, then this step is compulsory.

2. Following the above instructions, mmdetection is installed on `dev` mode, any local modifications made to the code will take effect without the need to reinstall it (unless you submit some commits and want to update the version number).

### Prepare COCO dataset

It is recommended to symlink the dataset root to `$MMDETECTION/data`.
If your folder structure is different, you may need to change the corresponding paths in config files.

```
mmdetection
├── mmdet
├── tools
├── configs
├── data
│   ├── coco
│   │   ├── annotations
│   │   ├── train2017
│   │   ├── val2017
│   │   ├── test2017
│   ├── cityscapes
│   │   ├── annotations
│   │   ├── train
│   │   ├── val
│   ├── VOCdevkit
│   │   ├── VOC2007
│   │   ├── VOC2012

```
The cityscapes annotations have to be converted into the coco format using the [cityscapesScripts](https://github.com/mcordts/cityscapesScripts) toolbox.
We plan to provide an easy to use conversion script. For the moment we recommend following the instructions provided in the 
[maskrcnn-benchmark](https://github.com/facebookresearch/maskrcnn-benchmark/tree/master/maskrcnn_benchmark/data) toolbox. When using this script all images have to be moved into the same folder. On linux systems this can e.g. be done for the train images with:
```shell
cd data/cityscapes/
mv train/*/* train/
```

### Scripts

[Here](https://gist.github.com/hellock/bf23cd7348c727d69d48682cb6909047) is
a script for setting up mmdetection with conda.

### Multiple versions

If there are more than one mmdetection on your machine, and you want to use them alternatively, the recommended way is to create multiple conda environments and use different environments for different versions.

Another way is to insert the following code to the main scripts (`train.py`, `test.py` or any other scripts you run)
```python
import os.path as osp
import sys
sys.path.insert(0, osp.join(osp.dirname(osp.abspath(__file__)), '../'))
```
or run the following command in the terminal of corresponding folder.
```shell
export PYTHONPATH=`pwd`:$PYTHONPATH
```
