HoughLinesPointSet not working

[ShiddhamSharma]

Summary of your issue

HoughLinesPointSet not producing correct results

Environment

OpenCVSharp.Extensions and OpenCVSharp.Windows: 4.9.0.20240103
.Net TargetFramework: 8.0
OpenCV-Python: 4.10.0

Example code:

double rhoMin = 0.0, rhoMax = 360.0, rhoStep = 1.0;
double thetaMin = 0.0, thetaMax = Math.PI / 2.0, thetaStep = Math.PI / 180.0;
double range = 20;

double minAngle = 180 - range;
double maxAngle = 0 + range;

if (StepLines == "Vertical")
{
    minAngle = 90 - range;
    maxAngle = 90 + range;
}

Mat lines = new Mat();

Mat pointsMat = new Mat(points.Count, 1, MatType.CV_32FC2);
for (int i = 0; i < points.Count; i++)
{
    pointsMat.Set(i, new Vec2f((float)(points[i].X - X0), (float)(points[i].Y - Y0)));
}

Cv2.HoughLinesPointSet(pointsMat, lines, 10, 1, rhoMin, rhoMax, rhoStep, thetaMin, thetaMax, thetaStep);

# Plot each point on the blank image
for point in points:
    x, y = int(point[0][0]), int(point[0][1])
    cv2.circle(image, (x, y), radius=3, color=(255, 0, 0), thickness=-1)

# Run HoughLinesPointSet if available
lines = cv2.HoughLinesPointSet(points, 1, 1, rho_min, rho_max, rho_step, theta_min, theta_max, theta_step)

for (int i = 0; i < lines.Rows; i++)
{
    Vec3f line = lines.Get<Vec3f>(i);
    float detectedVotes = line.Item0;
    float detectedRho = line.Item1;
    float detectedTheta = line.Item2;
}

Output

The line variable has three values: [a float value (depends on points), 0, 0]

In documentation, it says the output will be [votes, rho, theta].
But in my result, votes can be a decimal number, and rho and theta are always = 0.

[shimat]

Sorry for the late reply. I checked the HoughLinesPointSet with the following code and it seemed to work fine.

Vec2f[] points =
[
    new(0.0f, 369.0f),
    new(10.0f, 364.0f), 
    new(20.0f, 358.0f), 
    new(30.0f, 352.0f), 
    new(40.0f, 346.0f),
    new(50.0f, 341.0f), 
    new(60.0f, 335.0f), 
    new(70.0f, 329.0f), 
    new(80.0f, 323.0f),
    new(90.0f, 318.0f),
    new(100.0f, 312.0f), 
    new(110.0f, 306.0f), 
    new(120.0f, 300.0f), 
    new(130.0f, 295.0f),
    new(140.0f, 289.0f),
    new(150.0f, 284.0f),
    new(160.0f, 277.0f), 
    new(170.0f, 271.0f),
    new(180.0f, 266.0f),
    new(190.0f, 260.0f)
];

const int
    linesMax = 20,
    threshold = 1;
const double 
    rhoMin = 0.0f, 
    rhoMax = 360.0f, 
    rhoStep = 1,
    thetaMin = 0.0f,
    thetaMax = Cv2.PI / 2.0f, 
    thetaStep = Cv2.PI / 180.0f;

using var pointsMat = new Mat(points.Length, 1, MatType.CV_32FC2);
pointsMat.SetArray(points);
using var linesMat = new Mat();
Cv2.HoughLinesPointSet(pointsMat, linesMat, linesMax, threshold, rhoMin, rhoMax, rhoStep, thetaMin, thetaMax, thetaStep); 

linesMat.GetArray(out Vec3d[] lines);
var (votes, rho, theta) = lines[0];
Console.WriteLine("votes={0}, rho={1}, theta={2}", votes, rho, theta);  
// votes=19, rho=320, theta=1.0471975803375244

Please check if you are handling the output Mat type correctly (the type of lines is 64FC3 instead of 32FC3).