## Installation

### Requirements

- Linux (Windows is not officially supported)
- Python 3.5+
- 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: 9.0/9.2/10.0/10.1
- NCCL: 2.1.15/2.2.13/2.3.7/2.4.2
- GCC(G++): 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 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
pip install mmcv
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).

3. If you would like to use `opencv-python-headless` instead of `opencv-python`,
you can install it before installing MMCV.

### Another option: Docker Image

We provide a [Dockerfile](https://github.com/open-mmlab/mmdetection/blob/master/docker/Dockerfile) to build an image.

```shell
# build an image with PyTorch 1.1, CUDA 10.0 and CUDNN 7.5
docker build -t mmdetection docker/
```

### Prepare datasets

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/
```

### A from-scratch setup script

Here is a full script for setting up mmdetection with conda and link the dataset path.

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

conda install -c pytorch pytorch torchvision -y
conda install cython -y
git clone https://github.com/open-mmlab/mmdetection.git
cd mmdetection
pip install -v -e .

mkdir data
ln -s $COCO_ROOT data
```

### Using multiple MMDetection 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 to temporally use the current one.
```shell
export PYTHONPATH=`pwd`:$PYTHONPATH
```