Segment Length

OK, that's not too difficult.

You need to calculate perpendicular lines from the two vertices then calculate the distance between the points where these lines intersect one of the segments. The following code should help you.

defun( DE_linePerpendicular (m1, x, y)

 let((m2, b2)

cond(

(!m1, list(0, y))

(axlGeoEqual(m1, 0), list(nil, x))

(t, m2 = -1.0 / float(m1), b2 = y - m2 * x, list(m2, b2))

)

))

defun( DE_LineLineIntersect (m1, b1, m2, b2)

 let((x)

;  Returns x,y intersection of line

;     y = m1 x + b1

;  with line

;     y = m2 x + b2

;  Returns nil if no or infinite no of points (i.e. m1 = m2)

;

;  m1x + b1 = m2x + b2

;  x = (b2 - b1)/(m1 - m2)

;  y = m1 x + b1

cond(

(!m1 && !m2, nil)

(!m1, list(b1, m2 * b1 + b2)) ; ie. x = b1 for first line (not both nil!)

(!m2, list(b2, m1 * b2 + b1)) ; ie. x = b2 for 2nd line (not both nil!)

(m1 == m2, nil)

(t, x = (b2 - b1) / (m1 - m2), list(x, m1 * x + b1))

)

))

defun( DE_LineEquation (pt1, pt2)

 let((m, b)

;  Returns (m, b) s.t. y = mx + b is the equation for the line joining points (x1,y1) and (x2,y2)

;  Returns (nil, x) if vertical

m = axlLineSlope(list(pt1, pt2))

b = if(m then cadr(pt1) - m * car(pt1) else float(car(pt1)))

list(m, b)

)) 

OK, that's not too difficult.

You need to calculate perpendicular lines from the two vertices then calculate the distance between the points where these lines intersect one of the segments. The following code should help you.

defun( DE_linePerpendicular (m1, x, y)

 let((m2, b2)

cond(

(!m1, list(0, y))

(axlGeoEqual(m1, 0), list(nil, x))

(t, m2 = -1.0 / float(m1), b2 = y - m2 * x, list(m2, b2))

)

))

defun( DE_LineLineIntersect (m1, b1, m2, b2)

 let((x)

;  Returns x,y intersection of line

;     y = m1 x + b1

;  with line

;     y = m2 x + b2

;  Returns nil if no or infinite no of points (i.e. m1 = m2)

;

;  m1x + b1 = m2x + b2

;  x = (b2 - b1)/(m1 - m2)

;  y = m1 x + b1

cond(

(!m1 && !m2, nil)

(!m1, list(b1, m2 * b1 + b2)) ; ie. x = b1 for first line (not both nil!)

(!m2, list(b2, m1 * b2 + b1)) ; ie. x = b2 for 2nd line (not both nil!)

(m1 == m2, nil)

(t, x = (b2 - b1) / (m1 - m2), list(x, m1 * x + b1))

)

))

defun( DE_LineEquation (pt1, pt2)

 let((m, b)

;  Returns (m, b) s.t. y = mx + b is the equation for the line joining points (x1,y1) and (x2,y2)

;  Returns (nil, x) if vertical

m = axlLineSlope(list(pt1, pt2))

b = if(m then cadr(pt1) - m * car(pt1) else float(car(pt1)))

list(m, b)

))