November 22, 2006

Line Following Prototype

Using my previous prototypes I created a line following program. Given two initial points that indicate the start point and heading, it is able to follow a line drawn on my sample image.

The key function is:
def NextPoint(prevGradient : double, prevStartPoint : Point, prevEndPoint : Point, radius : int, bmp : Bitmap) : (double * Point * Point)

It takes
  • previous gradient
  • line segment (start and end points)
  • pixel capture radius
  • bitmap
    and returns
  • gradient of the next line segment
  • the improved end point for the previous line segment
  • the end point of the new line segment

Repeatedly calling this function passing in the previous data follows the line. The “improved end point” return is the intersection of the previous and current line segments – this make the polyline fit much better around corners. Without that it will overshoot then swing back each time.

I will not post the code here because frankily it’s getting messy! Also I am having some real difficulty expressing vertical lines as Infinite gradients and an X-intercept. It is now time to introduce some proper data structures to represent lines, etc, and better methods of calculating intercept points, etc.

One more quick idea:
Once the line follower has “used” some pixels should they be “removed” to prevent later confusion? I could not remove after one step, since previous pixels are used to shape the current line segment. But the pixels two-steps back should now be out of range. This would also stop the NextPoint function “turning around” at a dead-end.

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