PhotonVision/docs/source/docs/simulation/hardware-in-the-loop-sim.md

# Hardware In The Loop Simulation

Hardware in the loop simulation is using a physical device, such as a supported co-processor running PhotonVision, to enhance simulation capabilities. This is useful for developing and validating code before the camera is attached to a robot, as well as reducing the work required to use WPILib simulation with PhotonVision.

Before continuing, ensure PhotonVision is installed on your device. Instructions can be found {ref}`here <docs/advanced-installation/index:Advanced Installation>` for all devices.

Your coprocessor and computer running simulation will have to be connected to the same network, like a home router. Connecting the coprocessor directly to the computer will not work.

To simulate with hardware in the loop, a one-line change is required. From the PhotonVision UI, go to the sidebar and select the Settings option. Within the Networking settings, find "Team Number/NetworkTables Server Address".

During normal robot operation, a team's number would be entered into this field so that the PhotonVision coprocessor connects to the roboRIO as a NT client. Instead, enter the IP address of your computer running the simulation here.

:::{note}
To find the IP address of your Windows computer, open command prompt and run `ipconfig`.

```console
C:/Users/you>ipconfig

Windows IP Configuration

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : home
   Link-local IPv6 Address . . . . . : fe80::b41d:e861:ef01:9dba%10
   IPv4 Address. . . . . . . . . . . : 192.168.254.13
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.254.254
```

:::

```{image} images/coproc-client-to-desktop-sim.png

```

No code changes are required, PhotonLib should function similarly to normal operation.

Now launch simulation, and you should be able to see the PhotonVision table on your simulation's NetworkTables dashboard.

```{image} images/hardware-in-the-loop-sim.png

```