Answer to a question no one asked

Dar Scott dsc at
Tue Jan 25 13:59:10 EST 2005

On Jan 6, 2005, at 8:40 AM, James Hurley wrote:

> What is the perpendicular distance between a point and a line?

I was grading my daughter's math papers and thought of a couple things 
related to this.

1.  It is possible to create the general line parameters A, B and C of 
Ax + By + C =0 without any division, so no 'if' is needed.  This can be 
normalized by dividing by sqrt( A^2 + B^2 ), and since both A and B 
can't be 0 (assuming the two points defining the line are not 
identical), there is no division by zero here either.

If you save the line description in normal form at mouse down then you 
can calculate the distance at mouseMove faster.  It is simply Ax + By + 
C, where (x,y) is the point of interest.  This is the normalized A, B, 
& C where A = cos(omega) etc., the form you mentioned in other mail.

Dar Scott

     DSC (Dar Scott Consulting & Dar's Lab)
     Programming Services and Software

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