AreaG

[GP_]

Frequently, after a topographic survey, I have to prove the obtained area of a Lot of Land.
This lisp creates a table with the analytical method of the Gauss's area formula.
I do not need absolute precision, but logically (owing to rounding) by increasing decimal units you can get a result as close to the real one.

It is still to be completed, but I never have time to finish it.

You can change the nonsense I wrote in English 

AreaG.LSP

Edited July 25, 2020 by GP_

[GP_]

Customization 

 

[Lee Mac]

Wow! Astounding DCL work GP, very well done.

[Jonathan Handojo]

Agree with Lee Mac. That DCL is amazing. Though capable, I've never written one this big. 

[GP_]

@Lee   

@Jonathan

 

Thanks 

[marko_ribar]

I've run into this problem while inspired with this topic...

To explain... According to math and lisp that implemented math, area of closed 2d spline should be equal to (vla-get-area) or (vlax-curve-getarea) or data from Properties panel... But routine gives approx. correct, but little less... I know that there is curving involved, but 100000 points is very dense, so there should be no bigger difference and by my testings - difference is seen at very first decimals - how can this be true? Can someone explain or elaborate or retest my research...

 

(defun c:areaclosed2dspline ( / s spl n dx k pl ar )

  (vl-load-com)

  (while
    (or
      (prompt "\nPick closed 2d spline in WCS...")
      (not (setq s (ssget "_+.:E:S" '((0 . "SPLINE")))))
      (if s
        (or
          (not (vlax-curve-isclosed (ssname s 0)))
          (not (vl-every '(lambda ( x ) (equal (cadddr x) 0.0 1e-6)) (vl-remove-if-not '(lambda ( x ) (vl-position (car x) '(10 11))) (entget (ssname s 0)))))
        )
      )
    )
    (prompt "\nMissed or picked spline not closed or picked spline not in WCS...")
  )
  (setq spl (ssname s 0))
  (initget 6)
  (setq n (getreal "\nSpecify precision segmentation <100000> : "))
  (if (null n)
    (setq n 100000)
    (setq n (fix n))
  )
  (setq dx (/ (vlax-curve-getdistatparam spl (vlax-curve-getendparam spl)) n))
  (setq k -1)
  (repeat n
    (setq pl (cons (vlax-curve-getpointatdist spl (* dx (setq k (1+ k)))) pl))
  )
  (setq pl (reverse pl))
  (setq ar (abs (apply '+ (mapcar '(lambda ( a b ) (/ (- (* (car a) (cadr b)) (* (cadr a) (car b))) 2.0)) pl (append (cdr pl) (list (car pl)))))))
  (prompt "\nArea of closed 2d spline : ") (princ (rtos ar 2 20))
  (princ)
)

 

[marko_ribar]

Discard my post...

I retested with another 2d spline and now routine returned little bigger result and difference was at 4th decimal, so it's accurate...

Thanks for reading anyway...

[BIGAL]

As you say there is the little bit of the arc segment area left out,  unless there is a way of working out the approx radius between points on the spline  the area will say always be a bit less. Spline like a "U" shape would be different again with + & - areas