Topic: Find known object inside a block

[kenkrupa]

Some dynamic blocks each contain a circle. For any insertion of that block, I want to find the center point of that circle. It will always lie in the World plane, but it's relation to the insertion point varies when a dynamic angle changes. I need to find the center of this circle. Any way to do this?

[Lee Mac]

You should be able to use the center of the circle found within the anonymous block definition that is automatically generated for the dynamic block reference when the dynamic parameters are altered.

You would then transform the center coordinates to account for the block reference position, scale & rotation using an appropriate transformation matrix - for this I would recommend gile's refgeom function.

[kenkrupa]

Thank you much Lee, and gile too. That matrix stuff is something I would never figure out myself. Going into Thanksgiving day here, so it may be a few days before I can apply this, but I'm thankful for it already!

[Lee Mac]

You're most welcome ken 

Here is a quick & simple example program for you to test:

Code - Auto/Visual Lisp: [Select]

1. (defun c:cc ( / blk bln blx cen ent enx lst )
2.     (while
3.         (progn
4.             (setvar 'errno 0)
5.             (setq blk (car (entsel "\nSelect block: "))
6.                   cen nil
7.             )
8.             (cond
9.                 (   (= 7 (getvar 'errno))
10.                     (princ "\nMissed, try again.")
11.                 )
12.                 (   (null blk)
13.                     nil
14.                 )
15.                 (   (/= "INSERT" (cdr (assoc 0 (setq blx (entget blk)))))
16.                     (princ "\nPlease select a block.")
17.                 )
18.                 (   (not
19.                         (or (setq bln (cdr (assoc 2 blx))
20.                                   cen (cdr (assoc bln lst))
21.                             )
22.                             (progn
23.                                 (setq ent (tblobjname "block" bln))
24.                                 (while
25.                                     (and
26.                                         (null cen)
27.                                         (setq ent (entnext ent))
28.                                     )
29.                                     (if (= "CIRCLE" (cdr (assoc 0 (setq enx (entget ent)))))
30.                                         (setq cen (trans (cdr (assoc 10 enx)) (cdr (assoc 210 enx)) 0))
31.                                     )
32.                                 )
33.                                 (if cen (setq lst (cons (cons bln cen) lst)))
34.                             )
35.                         )
36.                     )
37.                     (princ "\nSelected block does not contain a circle.")
38.                 )
39.                 (   (entmake
40.                         (list
41.                            '(0 . "POINT")
42.                             (cons 10 (apply '(lambda ( m v ) (mapcar '+ (mxv m cen) v)) (refgeom blk)))
43.                         )
44.                     )
45.                 )
46.             )
47.         )
48.     )
49.     (princ)
50. )
51.  
52. ;; RefGeom (gile)
53. ;; Returns a list whose first item is a 3x3 transformation matrix and
54. ;; second item the object insertion point in its parent (xref, block or space)
55.  
56. (defun refgeom ( ent / ang enx mat ocs )
57.     (setq enx (entget ent)
58.           ang (cdr (assoc 050 enx))
59.           ocs (cdr (assoc 210 enx))
60.     )
61.     (list
62.         (setq mat
63.             (mxm
64.                 (mapcar '(lambda ( v ) (trans v 0 ocs t))
65.                    '(
66.                         (1.0 0.0 0.0)
67.                         (0.0 1.0 0.0)
68.                         (0.0 0.0 1.0)
69.                     )
70.                 )
71.                 (mxm
72.                     (list
73.                         (list (cos ang) (- (sin ang)) 0.0)
74.                         (list (sin ang) (cos ang)     0.0)
75.                        '(0.0 0.0 1.0)
76.                     )
77.                     (list
78.                         (list (cdr (assoc 41 enx)) 0.0 0.0)
79.                         (list 0.0 (cdr (assoc 42 enx)) 0.0)
80.                         (list 0.0 0.0 (cdr (assoc 43 enx)))
81.                     )
82.                 )
83.             )
84.         )
85.         (mapcar '- (trans (cdr (assoc 10 enx)) ocs 0)
86.             (mxv mat (cdr (assoc 10 (tblsearch "block" (cdr (assoc 2 enx))))))
87.         )
88.     )
89. )
90.  
91. ;; Matrix Transpose  -  Doug Wilson
92. ;; Args: m - nxn matrix
93.  
94. (defun trp ( m )
95.     (apply 'mapcar (cons 'list m))
96. )
97.  
98. ;; Matrix x Matrix  -  Vladimir Nesterovsky
99. ;; Args: m,n - nxn matrices
100.  
101. (defun mxm ( m n )
102.     ((lambda ( a ) (mapcar '(lambda ( r ) (mxv a r)) m)) (trp n))
103. )
104.  
105. ;; Matrix x Vector  -  Vladimir Nesterovsky
106. ;; Args: m - nxn matrix, v - vector in R^n
107.  
108. (defun mxv ( m v )
109.     (mapcar '(lambda ( r ) (apply '+ (mapcar '* r v))) m)
110. )
111.  
112. (princ)

The program will generate a POINT entity at the center of the first circle found in the block definition (this could easily be altered to match circles based on criteria such as layer / linetype / colour / handle etc.)

Here is a demonstration using a simple dynamic block with a dynamic move parameter assigned to the circle:

[kenkrupa]

Perfect! Thank you!