Warning

Warning: Unity Simulation is deprecated as of December 2023, and is no longer available.

Set up Data Logging

Now that you have a working simulation, you'll want it to emit some data for analysis. Depending on how you want to do your analysis, you might find it useful to output a CSV file (to load in plotly, for example), or some JSON, or perhaps a custom ROS message for another package to receive.

Writing to CSV

CSV is a very easy file format to generate, especially if you're just logging sets of numbers. Here's a simple C# utility class that receives rows of numbers and saves the results to a CSV file.

using System.IO;
using System.Linq;

class CsvLogger
{
    StreamWriter file;

    public CsvLogger(string filename)
    {
        file = new StreamWriter(filename);
    }

    public CsvLogger(string filename, params string[] columnNames): this(filename)
    {
        file.WriteLine(string.Join(\",\", columnNames));
    }

    public void AddRow(params float[] values)
    {
        file.WriteLine(string.Join(\",\", values.Select(f=>f.ToString())));
    }

    public void Close()
    {
        file.Close();
    }
}

And here's a simple Unity MonoBehaviour script that demonstrates how to use CsvLogger. You can just attach this component to a GameObject to log that object's height every frame:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CsvLoggerExample : MonoBehaviour
{
    CsvLogger logger;
    void Start()
    {
        logger = new CsvLogger(\"example.csv\", \"height\", \"time\");
    }

    void Update()
    {
        logger.AddRow(transform.position.y, Time.time);
    }

    void OnApplicationQuit()
    {
        logger.Close();
    }
}

Writing data as JSON

The JsonUtility class is a fast, convenient way to convert simple data structures into JSON format, although it can't generate all possible Json files.

Here's an example of a MonoBehaviour that collects data about the height of its GameObject over time. When it has collected enough data points, it publishes them as a JSON string embedded in a ROS String message, and then turns itself off.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.Simulation.Foundation;
using Unity.Simulation.Foundation.StdMessages;

public class JsonLoggerExample : MonoBehaviour
{
    [SerializeField]
    string topic = \"jsonlog\";

    // This class's fields are the keys of the json dictionary we will generate
    class JsonData
    {
        public List<float> heights = new List<float>();
        public List<float> times = new List<float>();
    }
    JsonData data;
    IPublisher publisher;

    void Start()
    {
        data = new JsonData();
        publisher = ConnectorInjector.FindConnection(gameObject).RegisterPublisher<StringMsg>(topic);
    }

    void Update()
    {
        data.heights.Add(transform.position.y);
        data.times.Add(Time.time);

        // When we have enough data, generate the json, send it and turn off the logger
        if (data.heights.Count >= 100)
        {
            this.enabled = false; // stop updating

            string json = JsonUtility.ToJson(data);
            publisher.Publish(new StringMsg(json));
        }
    }
}