private static CoordinateSystemGrid FindForPlaneCalibration(CalibrationHelper calibrationHelper)
{
CoordinateSystemGrid grid = new CoordinateSystemGrid();
RectangleF imageBounds = new RectangleF(PointF.Empty, calibrationHelper.ImageSize);
RectangleF clipWindow = imageBounds;
CalibrationPlane calibrator = calibrationHelper.CalibrationByPlane_GetCalibrator();
RectangleF plane = new RectangleF(PointF.Empty, calibrator.Size);
int targetSteps = 15;
float stepVertical = 1.0f;
float stepHorizontal = 1.0f;
// The extended plane is used for vanishing point replacement and iteration stop condition.
QuadrilateralF extendedPlane;
bool orthogonal;
if (!calibrator.QuadImage.IsRectangle)
{
// If perspective plane, define as 2n times the nominal plane centered on origin.
orthogonal = false;
float n = 4;
PointF a = new PointF(-calibrator.Size.Width * n, calibrator.Size.Height * n);
PointF b = new PointF(calibrator.Size.Width * n, calibrator.Size.Height * n);
PointF c = new PointF(calibrator.Size.Width * n, -calibrator.Size.Height * n);
PointF d = new PointF(-calibrator.Size.Width * n, -calibrator.Size.Height * n);
extendedPlane = new QuadrilateralF(a, b, c, d);
QuadrilateralF quadImage = calibrator.QuadImage;
float projectedWidthLength = GeometryHelper.GetDistance(quadImage.A, quadImage.B);
float scaledTargetHorizontal = targetSteps / (calibrationHelper.ImageSize.Width / projectedWidthLength);
stepHorizontal = RangeHelper.FindUsableStepSize(plane.Width, scaledTargetHorizontal);
float projectedHeightLength = GeometryHelper.GetDistance(quadImage.A, quadImage.D);
float scaledTargetVertical = targetSteps / (calibrationHelper.ImageSize.Height / projectedHeightLength);
stepVertical = RangeHelper.FindUsableStepSize(plane.Height, scaledTargetVertical);
}
else
{
// If flat plane (and no distortion) we know there is no way to get any vanishing point inside the image,
// so we can safely use the whole image reprojection as an extended plane.
orthogonal = true;
QuadrilateralF quadImageBounds = new QuadrilateralF(imageBounds);
PointF a = calibrationHelper.GetPointFromRectified(quadImageBounds.A);
PointF b = calibrationHelper.GetPointFromRectified(quadImageBounds.B);
PointF c = calibrationHelper.GetPointFromRectified(quadImageBounds.C);
PointF d = calibrationHelper.GetPointFromRectified(quadImageBounds.D);
extendedPlane = new QuadrilateralF(a, b, c, d);
float width = extendedPlane.B.X - extendedPlane.A.X;
stepHorizontal = RangeHelper.FindUsableStepSize(width, targetSteps);
float height = extendedPlane.A.Y - extendedPlane.D.Y;
stepVertical = RangeHelper.FindUsableStepSize(height, targetSteps);
}
//-------------------------------------------------------------------------------------------------
// There is a complication with points behind the camera, as they projects above the vanishing line.
// The general strategy is the following:
// Find out if the vanishing point is inside the image. Reminder: parallel lines share the same vanishing point.
// If it is not inside the image, there is no risk, so we take two points on the line and draw an infinite line that we clip against the image bounds.
// If it is inside the image:
// Take two points on the line and project them in image space. They are colinear with the vanishing point in image space.
// Find on which side of the quadrilateral the vanishing point is.
// If the vanishing point is above the quad, draw a ray from the top of the extended quad, down to infinity.
// If the vanishing point is below the quad, draw a ray from the bottom of the extended quad, up to infinity.
//
// Stepping strategy:
// We start at origin and progress horizontally and vertically until we find a gridline that is completely clipped out.
//-------------------------------------------------------------------------------------------------
// Vertical lines.
PointF yVanish = new PointF(0, float.MinValue);
bool yVanishVisible = false;
Vector3 yv = calibrator.Project(new Vector3(0, 1, 0));
if (yv.Z != 0)
{
yVanish = new PointF(yv.X / yv.Z, yv.Y / yv.Z);
yVanishVisible = clipWindow.Contains(yVanish);
}
CreateVerticalGridLines(grid, 0, -stepHorizontal, calibrator, clipWindow, plane, extendedPlane, orthogonal, yVanishVisible, yVanish);
CreateVerticalGridLines(grid, stepHorizontal, stepHorizontal, calibrator, clipWindow, plane, extendedPlane, orthogonal, yVanishVisible, yVanish);
// Horizontal lines
PointF xVanish = new PointF(float.MinValue, 0);
bool xVanishVisible = false;
Vector3 xv = calibrator.Project(new Vector3(1, 0, 0));
if (xv.Z != 0)
{
xVanish = new PointF(xv.X / xv.Z, xv.Y / xv.Z);
xVanishVisible = clipWindow.Contains(xVanish);
}
CreateHorizontalGridLines(grid, 0, -stepVertical, calibrator, clipWindow, plane, extendedPlane, orthogonal, xVanishVisible, xVanish);
CreateHorizontalGridLines(grid, stepVertical, stepVertical, calibrator, clipWindow, plane, extendedPlane, orthogonal, xVanishVisible, xVanish);
return(grid);
}
private static void CreateHorizontalGridLines(CoordinateSystemGrid grid, float start, float step, CalibrationPlane calibrator, RectangleF clipWindow, RectangleF plane, QuadrilateralF extendedPlane, bool orthogonal, bool vanishVisible, PointF vanish)
{
// Progress from origin to the side until grid lines are no longer visible when projected on image.
float y = start;
bool partlyVisible = true;
while (partlyVisible && y >= extendedPlane.D.Y && y <= extendedPlane.A.Y)
{
Vector3 pa = calibrator.Project(new PointF(0, y));
Vector3 pb = calibrator.Project(new PointF(plane.Width, y));
// Discard line if one of the points is behind the camera.
if (pa.Z < 0 || pb.Z < 0)
{
y += step;
continue;
}
PointF a = new PointF(pa.X / pa.Z, pa.Y / pa.Z);
PointF b = new PointF(pb.X / pb.Z, pb.Y / pb.Z);
ClipResult result;
if (vanishVisible)
{
float scale = (b.X - a.X) / (vanish.X - a.X);
if (scale > 0)
{
// Vanishing point is after b.
PointF vb = calibrator.Untransform(new PointF(extendedPlane.B.X, y));
result = LiangBarsky.ClipLine(clipWindow, a, vb, double.MinValue, 1);
}
else
{
// Vanishing point is before a.
PointF va = calibrator.Untransform(new PointF(extendedPlane.A.X, y));
result = LiangBarsky.ClipLine(clipWindow, va, b, 0, double.MaxValue);
}
}
else
{
result = LiangBarsky.ClipLine(clipWindow, a, b);
}
partlyVisible = result.Visible;
if (partlyVisible)
{
if (y == 0)
{
grid.HorizontalAxis = new GridAxis(result.A, result.B);
}
else
{
grid.GridLines.Add(new GridLine(result.A, result.B));
if (clipWindow.Contains(a) && (orthogonal || TickMarkVisible((int)(y / step))))
{
grid.TickMarks.Add(new TickMark(y, a, TextAlignment.Left));
}
}
}
y += step;
}
}