How to select polylines at a certain elevation ???

Ok Guys,

I am trying to select a polyline which represents a contour.
This polyline has all its vertices at the same elevation (like every good
contour should)

The code I am using is

......
(setq elevation 60.5)
(setq S (ssget "X" (list (cons 38 elevation))))
......

This doesnt return anything yet there are several contours at that elevation

From what I can tell its something a little tricky with the way polyline
entities are handled

Any help appreciated.

Regards
Dave

 

Anyone ????

I have gone about it differently but I am sure it is not elegant

Got some clues off the afralisp site

It works though and that is the main point

But my question still applies about the selecting polylines at a constant
elevation using a filter ?

Is it possible ???

Anyway this is what I did

(Defun C:contour_stripper (/)
(setq start_contour 0.5)
(setq end_contour 150.5)
(setq interval 1)
(setq current_contour start_contour)
(setq stripped_layer "STRIPPED")
(command "layer" "m" stripped_layer "")
(while (> end_contour current_contour)
(grtext -2 (strcat (itoa (fix (* (/ current_contour end_contour) 100)))"%
Complete"))
(setq S (ssget "X" (list (cons 0 "POLYLINE"))))
(setq sss (ssadd))
(setq numofentities (sslength s))
(setq entity_index 0.0)
(repeat numofentities
(setq current_entity (entget (ssname s entity_index)))
(setq e1 (entget (entnext (cdr (car current_entity)))))
(setq current_entity_elevation (car (cdddr (assoc 10 e1))))
(if (= current_entity_elevation current_contour)
(progn
(ssadd (ssname s entity_index) sss)
(command "change" sss "" "p" "la" stripped_layer "")
);end progn
);end if
(setq entity_index (+ entity_index 1))
);end repeat
(setq current_contour (+ current_contour interval))
);end while
);end of defun

;this routine rips contours to a separate layer for deletion