Represents line of Hough Line transformation using polar coordinates. See Wikipedia for information on how to convert polar coordinates to Cartesian coordinates.
Sample code to draw detected Hough lines:
HoughLineTransformation lineTransform = new HoughLineTransformation( ); // apply Hough line transofrm lineTransform.ProcessImage( sourceImage ); Bitmap houghLineImage = lineTransform.ToBitmap( ); // get lines using relative intensity HoughLine[] lines = lineTransform.GetLinesByRelativeIntensity( 0.5 ); foreach ( HoughLine line in lines ) { // get line's radius and theta values int r = line.Radius; double t = line.Theta; // check if line is in lower part of the image if ( r < 0 ) { t += 180; r = -r; } // convert degrees to radians t = ( t / 180 ) * Math.PI; // get image centers (all coordinate are measured relative // to center) int w2 = image.Width /2; int h2 = image.Height / 2; double x0 = 0, x1 = 0, y0 = 0, y1 = 0; if ( line.Theta != 0 ) { // none-vertical line x0 = -w2; // most left point x1 = w2; // most right point // calculate corresponding y values y0 = ( -Math.Cos( t ) * x0 + r ) / Math.Sin( t ); y1 = ( -Math.Cos( t ) * x1 + r ) / Math.Sin( t ); } else { // vertical line x0 = line.Radius; x1 = line.Radius; y0 = h2; y1 = -h2; } // draw line on the image Drawing.Line( sourceData, new IntPoint( (int) x0 + w2, h2 - (int) y0 ), new IntPoint( (int) x1 + w2, h2 - (int) y1 ), Color.Red ); } To clarify meaning of Radius and Theta values of detected Hough lines, let's take a look at the below sample image and corresponding values of radius and theta for the lines on the image:
Detected radius and theta values (color in corresponding colors):
// Get specified amount of lines with highest intensity
private HoughLine[] GetMostIntensiveLines(int count)
{
// lines count
int n = Math.Min(count, lines.Count);
// result array
HoughLine[] dst = new HoughLine[n];
lines.CopyTo(0, dst, 0, n);
return(dst);
}
/// <summary>
/// Get specified amount of lines with highest <see cref="HoughLine.Intensity">intensity</see>.
/// </summary>
///
/// <param name="count">Amount of lines to get.</param>
///
/// <returns>Returns array of most intesive lines. If there are no lines detected,
/// the returned array has zero length.</returns>
///
public HoughLine[] GetMostIntensiveLines(int count)
{
// lines count
var n = Math.Min(count, this.lines.Count);
// result array
var dst = new HoughLine[n];
this.lines.CopyTo(0, dst, 0, n);
return(dst);
}
// Get specified amount of lines with highest intensity
private HoughLine[] GetMostIntensiveLines( int count )
{
// lines count
int n = Math.Min( count, lines.Count );
// result array
HoughLine[] dst = new HoughLine[n];
lines.CopyTo( 0, dst, 0, n );
return dst;
}
// Get lines using theirs intensity value [0, 1]
public HoughLine[] GetLinesByIntensity(double intensity)
{
short minIntensity = (short)(maxMapValue * intensity);
int maxTheta = houghMap.GetLength(0);
int maxR = houghMap.GetLength(1);
short v;
bool foundMax;
int halfHoughWidth = maxR >> 1;
ArrayList linesList = new ArrayList( );
// for each Theta value
for (int theta = 0; theta < maxTheta; theta++)
{
// for each R value
for (int r = 0; r < maxR; r++)
{
// get current value
v = houghMap[theta, r];
foundMax = false;
if (v < minIntensity)
{
continue;
}
// check neighboors
for (int tt = theta - localPeakRadius, ttMax = theta + localPeakRadius; tt < ttMax; tt++)
{
if (tt < 0)
{
continue;
}
if ((foundMax == true) || (tt >= maxTheta))
{
break;
}
for (int tr = r - localPeakRadius, trMax = r + localPeakRadius; tr < trMax; tr++)
{
if ((tr < 0) || ((tr == r) && (tt == theta)))
{
continue;
}
if (tr >= maxR)
{
break;
}
// compare the neighboor with current value
if (houghMap[tt, tr] > v)
{
foundMax = true;
break;
}
}
}
//
if (!foundMax)
{
// we have local maximum
linesList.Add(new HoughLine((short)theta, (short)(r - halfHoughWidth), v));
}
}
}
//
int linesCount = linesList.Count;
HoughLine[] lines = new HoughLine[linesCount];
for (int i = 0; i < linesCount; i++)
{
lines[i] = (HoughLine)linesList[i];
}
return(lines);
}
