Topic: Calculating points

[Shade]

I am writing a lisp to draw a gable roof, and I am having trouble calculating the points necessary to complete the roof.
I am having trouble calculating points PT6 and PT7 in the example provided.
PT6 and PT7 are needed to get PT8.
All other points listed in the example (attached) I have already found.
The rise of the roof is a variable number from 1 to 12 and therefore the pitch will always be a number over 12.
All other dimensions in the example are fixed and will never change.
Any  help would be greatly appreciated.
Thanks in advance…

[Keith™]

Quick and dirty ... should be self explanitory .. lots of cleanup could be performed with it as well ..

Code: [Select]

(defun getPnt (pt1 pt2 pt5)
  (setq temppt1 (polar pt1 (- (angle pt1 pt2) (ANGTOF "90")) 6)
temppt2 (polar pt2 (- (angle pt1 pt2) (ANGTOF "90")) 6)
temppt3 (polar pt5 (ANGTOF "90") 12)
temppt4 (polar pt2 (- (angle pt2 pt3) (angtof "90")) 6)
  )
  (setq pt7 (inters temppt1 temppt2 pt5 temppt3 nil)
pt6 (polar pt7 0 (- (distance pt1 pt3) 56))
pt8 (inters pt7 temppnt2 pt6 temppnt4 nil)
  )
  (vl-cmdf "_.line" pt7 pt8 pt6 "")
)


[Shade]

Thanks, Keith.
It took me a little while before I could see how you did it, but i got it.

Cheers mate!

[CAB]

Here is another take on the problem.

Code: [Select]

(defun c:test2 (/ p1 p2 p5 p7 p8 s1)

  (setq p1 (getpoint "\nPick point P1"))
  (setq p2 (getpoint "\nPick point P2"))
  (setq p5 (getpoint "\nPick point P5"))
  (setq s1 6.0)

  (setq p8 (polar p2 (* pi 1.5) (/ s1 (sin (- (/ pi 2) (angle p1 p2))))))
  (setq p7 (inters p5 (polar p5 (/ pi 2) 100)
                  p8 (polar p8 (angle p2 p1) 100) nil))

  (command ".point" "_non" p8)
  (command ".point" "_non" p7)

  (princ)
)