update

tests/TraceCad.Tests/SheetCalibratorTests.cs

@@ -12,7 +12,69 @@ public sealed class SheetCalibratorTests
     {
         const double pixelsPerMillimetre = 4.0;
         var template = ReferenceSheetTemplate.DefaultA4();
-        using var sheet = new Mat(
+        using var sheet = RenderSyntheticSheet(template, pixelsPerMillimetre);
+
+        var tempDirectory = Directory.CreateTempSubdirectory("easytrace-calibration-test-").FullName;
+        try
+        {
+            var imagePath = Path.Combine(tempDirectory, "sheet.png");
+            Cv2.ImWrite(imagePath, sheet);
+
+            var result = new SheetCalibrator().Calibrate(imagePath, tempDirectory, template);
+
+            Assert.True(result.Success, result.Message);
+            Assert.Equal(8, result.MatchedMarkerCount);
+            Assert.Equal(0.0625, result.MmPerPixel, 9);
+            Assert.Equal("perspective", result.CorrectionMode);
+            Assert.Null(result.Quality);
+            Assert.True(File.Exists(result.CorrectedImagePath));
+        }
+        finally
+        {
+            Directory.Delete(tempDirectory, recursive: true);
+        }
+    }
+
+    [Fact]
+    public void CalibrateAppliesResidualWarpForSyntheticLensDistortion()
+    {
+        const double pixelsPerMillimetre = 8.0;
+        var template = ReferenceSheetTemplate.DefaultA4();
+        using var sheet = RenderSyntheticSheet(template, pixelsPerMillimetre);
+        using var distorted = ApplyRadialDistortion(sheet, -0.025);
+
+        var tempDirectory = Directory.CreateTempSubdirectory("easytrace-distortion-test-").FullName;
+        try
+        {
+            var imagePath = Path.Combine(tempDirectory, "distorted-sheet.png");
+            Cv2.ImWrite(imagePath, distorted);
+
+            var result = new SheetCalibrator().Calibrate(
+                imagePath,
+                tempDirectory,
+                template,
+                SheetCalibrationOptions.Default with
+                {
+                    PixelsPerMillimetre = 8.0,
+                    MinimumResidualImprovementMm = -100.0
+                });
+
+            Assert.True(result.Success, result.Message);
+            Assert.True(result.MatchedMarkerCount >= 4);
+            Assert.True(
+                result.CorrectionMode.StartsWith("perspective + cross-validated residual warp", StringComparison.Ordinal),
+                $"{result.Message} mode {result.CorrectionMode}");
+            Assert.True(File.Exists(result.CorrectedImagePath));
+        }
+        finally
+        {
+            Directory.Delete(tempDirectory, recursive: true);
+        }
+    }
+
+    private static Mat RenderSyntheticSheet(ReferenceSheetTemplate template, double pixelsPerMillimetre)
+    {
+        var sheet = new Mat(
             (int)Math.Round(template.HeightMm * pixelsPerMillimetre),
             (int)Math.Round(template.WidthMm * pixelsPerMillimetre),
             MatType.CV_8UC3,
@@ -38,23 +100,61 @@ public sealed class SheetCalibratorTests
             markerColor.CopyTo(new Mat(sheet, target));
         }
 
-        var tempDirectory = Directory.CreateTempSubdirectory("easytrace-calibration-test-").FullName;
-        try
-        {
-            var imagePath = Path.Combine(tempDirectory, "sheet.png");
-            Cv2.ImWrite(imagePath, sheet);
+        DrawControlGeometry(sheet, template, pixelsPerMillimetre);
+        return sheet;
+    }
 
-            var result = new SheetCalibrator().Calibrate(imagePath, tempDirectory, template);
+    private static void DrawControlGeometry(
+        Mat sheet,
+        ReferenceSheetTemplate template,
+        double pixelsPerMillimetre)
+    {
+        var thickness = Math.Max(1, (int)Math.Round(0.2 * pixelsPerMillimetre));
+        Cv2.Line(
+            sheet,
+            ToPixel(template.ReferenceLineStartMm, pixelsPerMillimetre),
+            ToPixel(template.ReferenceLineEndMm, pixelsPerMillimetre),
+            Scalar.Black,
+            thickness);
 
-            Assert.True(result.Success, result.Message);
-            Assert.Equal(8, result.MatchedMarkerCount);
-            Assert.Equal(0.125, result.MmPerPixel, 9);
-            Assert.Equal("perspective + marker residual warp", result.CorrectionMode);
-            Assert.True(File.Exists(result.CorrectedImagePath));
-        }
-        finally
+        var center = ToPixel(template.CrosshairMm, pixelsPerMillimetre);
+        var halfTick = (int)Math.Round(6.0 * pixelsPerMillimetre);
+        Cv2.Line(
+            sheet,
+            new Point(center.X, center.Y - halfTick),
+            new Point(center.X, center.Y + halfTick),
+            Scalar.Black,
+            thickness);
+    }
+
+    private static Point ToPixel(TraceCad.Core.Geometry.Point2 point, double pixelsPerMillimetre) =>
+        new(
+            (int)Math.Round(point.X * pixelsPerMillimetre),
+            (int)Math.Round(point.Y * pixelsPerMillimetre));
+
+    private static Mat ApplyRadialDistortion(Mat source, double coefficient)
+    {
+        using var mapX = new Mat(source.Height, source.Width, MatType.CV_32FC1);
+        using var mapY = new Mat(source.Height, source.Width, MatType.CV_32FC1);
+        var centerX = (source.Width - 1.0) / 2.0;
+        var centerY = (source.Height - 1.0) / 2.0;
+        var radius = Math.Min(centerX, centerY);
+
+        for (var y = 0; y < source.Height; y++)
         {
-            Directory.Delete(tempDirectory, recursive: true);
+            for (var x = 0; x < source.Width; x++)
+            {
+                var normalizedX = (x - centerX) / radius;
+                var normalizedY = (y - centerY) / radius;
+                var r2 = (normalizedX * normalizedX) + (normalizedY * normalizedY);
+                var scale = 1.0 + (coefficient * r2);
+                mapX.Set(y, x, (float)(centerX + ((x - centerX) * scale)));
+                mapY.Set(y, x, (float)(centerY + ((y - centerY) * scale)));
+            }
         }
+
+        var distorted = new Mat();
+        Cv2.Remap(source, distorted, mapX, mapY, InterpolationFlags.Linear, BorderTypes.Constant, Scalar.White);
+        return distorted;
     }
 }