rem                            L_PtLn.cdl

rem        Copy Right by International Technology Transfer Corp.
rem        revision 1.0-7/30/99   



rem        ********************************************************************
rem        Line from Point perpendicular to specified line
rem        1. Indicate Point
rem        2. Select Line
rem        3. Draw the perpendicular line
rem        ********************************************************************

clear
defopt = 2

:start
	getpos "Indicate Point",defopt
	on (@key + 3) goto exit, start,start,
	defopt=@key
	x0 = @xworld
	y0 = @yworld
	z0 = @zworld
	
:line
	getent "Select Line",enttype
	on (@key + 3) goto exit, start, line, 
	if (enttype!=2)
		goto line
	x1 = @fltdat[0]
	y1 = @fltdat[1]
	z1 = @fltdat[2]
	x2 = @fltdat[3]
	y2 = @fltdat[4]
	z2 = @fltdat[5]
	
	f = x2 - x1
	g = y2 - y1
	h = z2 - z1
rem     ***********************************************************************
rem     equation for space
rem     x = x1 + f * t
rem     y = y1 + g * t
rem     z = z1 + h * t
rem     
rem     �i x1 + f * t�Ay1 + g * t�Az1 + h * t�j
rem     calculate t to minimize l below
rem     l*l = (x1 + f*t - x0)*(x1 + f*t - x0)
rem         + (y1 + g*t - y0)*(y1 + g*t - y0) + (z1 + h*t - z0)*(z1 + h*t - z0)
rem     when t = t0, minimum
rem     ( t0 = (f * (x0-x1) + g * (y0-y1) + h * (z0-z1)) / (f*f + g*g + h*h) )
rem     ***********************************************************************
	t = (f * (x0-x1) + g * (y0-y1) + h * (z0-z1)) / (f*f + g*g + h*h)

	x = x1 + f * t
	y = y1 + g * t
	z = z1 + h * t

	line x0, y0, z0, x, y, z

	redraw
	goto start
:exit