We are in land development sector and want the parcel creation tools to create lot around a curve to messure the min frontage from the cord of the curve and not the tangent of the curve? is this possible to achive? I do not see where to change this setting.
Please see attached................
Thanks
Solved! Go to Solution.
Solved by Jeff_M. Go to Solution.
Civil 3D does not provide any function to create lots based on the length of the chord.
Increase the min arc length until you get desirable results in the chord.
John Mayo
You will need to provide Civil3d with the tangent length needed to achieve the desired frontage at the real frontage. The radius & chord can be used to calc this quickly. Here's a simple lisp program to do this for you:
(defun c:outertan (/ chord halfchord outer radius ratio) (if (and (setq radius (getreal "\nRadius of arc: ")) (setq chord (getreal "\Length of chord: ")) ) (progn (setq halfchord (/ chord 2.0)) (setq ratio (/ radius (sqrt (- (* radius radius) (* halfchord halfchord) )))) (setq outer (* 2 (* ratio halfchord))) ) ) (princ (strcat "\nOuter tangent for this chord length is " (rtos outer 2 8))) (princ) )
The parcel sizing command use thactual length along the parcel frontage (or offset if that is used), not the chord distance. The following lisp will return the arc length needed to hold the specified chord distance.
(defun c:arclenfromchord (/ chord halfchord len radius delta) ;;; ASIN Returns the arcsinus of a number in radians (defun asin (num) (if (<= -1 num 1) (atan num (sqrt (- 1 (expt num 2)))) ) ) (if (and (setq radius (getreal "\nRadius of arc: ")) (setq chord (getreal "\Length of chord: ")) ) (progn (setq halfchord (/ chord 2.0)) (setq delta (* 2 (asin (* (/ 1 radius) halfchord)))) (setq len (* delta radius)) ) ) (princ (strcat "\nArc length for this chord length is " (rtos len 2 8) ) ) (princ) )
Here's an image which shows how the Parcel sizing uses the values for "Minimum frontage" and "Minimum frontage at offset". In this case, the offset is 15' and the desired distance on the chord is 64.00'. Using the lisp above to get the arc length for this curve, we get 64.088. This is the value I used in the Minimum frontage value. As evidenced by the curve label, this gives us the desired distance across the chord.