Hough transform from wiki

from wiki:

• For each data point, a number of lines are plotted going through it, all at different angles. These are shown here as solid lines.
• For each solid line a line is plotted which is perpendicular to it and which intersects the origin. These are shown as dashed lines.
• The length (i.e. perpendicular distance to the origin) and angle of each dashed line is measured. In the diagram above, the results are shown in tables.
• This is repeated for each data point.
• A graph of the line lengths for each angle, known as a Hough space graph, is then created.