Model/STLModel.cs

FastPrint/
│
├── Geometry/
│   └── BsplineMitchellNetravali.cs
│
├── Slicing/
│   └── SliceAccelerator.cs
│
├── Printer/
│   └── MarlinConnector.cs
│
├── Model/
│   └── STLModel.cs
│
├── UI/
│   ├── MainWindow.xaml
│   └── MainWindow.xaml.cs
│
└── README.md   

using System.Collections.Generic;
using System.IO;
using System.Globalization;

namespace FastPrint.Model
{
    public class STLModel
    {
        public List<float[]> Triangles { get; } = new List<float[]>();

        public void LoadAscii(string path)
        {
            using var reader = new StreamReader(path);
            string line;
            var currentTriangle = new List<float>();
            while ((line = reader.ReadLine()) != null)
            {
                if (line.Trim().StartsWith("vertex"))
                {
                    var parts = line.Trim().Split(' ');
                    for (int i = 1; i < 4; i++)
                        currentTriangle.Add(float.Parse(parts[i], CultureInfo.InvariantCulture));
                }
                if (currentTriangle.Count == 9)
                {
                    Triangles.Add(currentTriangle.ToArray());
                    currentTriangle.Clear();
                }
            }
        }
    }
}