Extracting Face and Edge Information from a 3D Solid Without Exploding It

[p7q]

Hello,

I want to collect detailed information about all faces of a `3DSOLID` without exploding or modifying the original solid.

For each face, I would like to obtain information such as:

* Face area
* Face type, such as planar, cylindrical or curved
* Boundary edges of the face
* Length of each edge
* Start and end points of each edge
* Which edges are shared by two adjacent faces
* Which faces are connected to each other through a common edge
* The angle between adjacent faces
* Face normal direction, where available

Ideally, I would like to store the result in a structured form similar to:

Is it possible to retrieve this topology directly using AutoLISP or Visual LISP without using `EXPLODE`?

Would this require the AutoCAD .NET BRep API or ObjectARX, or is there an existing AutoLISP approach?

Any examples, references or recommended methods would be helpful.

Thank you.

[mhupp]

50 minutes ago, p7q said:

without exploding or modifying the original solid.

Often times I would make a copy of a polyline explode it and work over its sub-parts deleting them as i go. no reason you shouldn't do the same here keep the original un touched, make a copy either to a new location or layer and explode and process each part. you shouldn't avoid explode just use it on the copy. 

 

-edit

https://www.cadtutor.net/forum/topic/34725-autocad2012-3d-solidsurface-into-3d-face/#findComment-281787

Edited 12 hours ago by mhupp

[Danielm103]

It’s possible with lisp, but really hard. When you entget a solid, you see the garbage at the end that looks like “{kn rn {rn {km rnqhlokhlhhjjnimjmoll {kl nqhlokhlhhjjnimjmoll”, you can actually decode that and get vertices, edges and faces.

 

Python, .NET, or ObjectARX you can use AcDbAssocPersSubentIdPE, It’s like a BRep shortcut. Or use Brep

 

from pyrx import Ap, Db, Ed, Ge, Br

print("added command pygetsubents")

def pygetsubents(ent: Db.Entity):
    pe = Db.AssocPersSubentIdPE(ent.queryX(Db.AssocPersSubentIdPE.desc()))
    print("vertex")
    for vtx in pe.getAllSubentities(ent, Db.SubentType.kVertexSubentType):
        # Get the geometric position of each vertex
        pos = pe.getVertexSubentityGeometry(ent, vtx)
        print(pos)

    print("edge")
    for edge in pe.getAllSubentities(ent, Db.SubentType.kEdgeSubentType):
        curve = pe.getEdgeSubentityGeometry(ent, edge)
        print(curve.getStartPoint(), curve.getEndPoint())

    print("surface")
    for face in pe.getAllSubentities(ent, Db.SubentType.kFaceSubentType):
        brface = Br.Face()
        brface.setSubentPath(Db.FullSubentPath(ent.objectId(), face))
        print("Area", brface.getArea())

@Ap.Command()
def doit():
    es, id, pnt = Ed.Editor.entSel("\nPick it: \n")
    ent = Db.Entity(id)
    pygetsubents(ent)
    

 

 

Command: DOIT
Pick it:
vertex
(117.71953884538620,11.77489209746249,100.00000000000000)
(117.71953884538620,16.43799615292209,100.00000000000000)
(17.71953884538620,16.43799615292209,100.00000000000000)
(17.71953884538620,11.77489209746249,100.00000000000000)
(117.71953884538620,16.43799615292209,0.00000000000000)
(117.71953884538620,11.77489209746249,0.00000000000000)
(17.71953884538620,11.77489209746249,0.00000000000000)
(17.71953884538620,16.43799615292209,0.00000000000000)
edge
(17.71953884538620,16.43799615292209,100.00000000000000) (117.71953884538620,16.43799615292209,100.00000000000000)
(117.71953884538620,16.43799615292209,0.00000000000000) (17.71953884538620,16.43799615292209,0.00000000000000)
(17.71953884538620,11.77489209746249,100.00000000000000) (17.71953884538620,16.43799615292209,100.00000000000000)
(17.71953884538620,16.43799615292209,100.00000000000000) (17.71953884538620,16.43799615292209,0.00000000000000)
(17.71953884538620,16.43799615292209,0.00000000000000) (17.71953884538620,11.77489209746249,0.00000000000000)
(117.71953884538620,11.77489209746249,100.00000000000000) (17.71953884538620,11.77489209746249,100.00000000000000)
(17.71953884538620,11.77489209746249,100.00000000000000) (17.71953884538620,11.77489209746249,0.00000000000000)
(17.71953884538620,11.77489209746249,0.00000000000000) (117.71953884538620,11.77489209746249,0.00000000000000)
(117.71953884538620,16.43799615292209,100.00000000000000) (117.71953884538620,16.43799615292209,0.00000000000000)
(117.71953884538620,16.43799615292209,100.00000000000000) (117.71953884538620,11.77489209746249,100.00000000000000)
(117.71953884538620,11.77489209746249,100.00000000000000) (117.71953884538620,11.77489209746249,0.00000000000000)
(117.71953884538620,11.77489209746249,0.00000000000000) (117.71953884538620,16.43799615292209,0.00000000000000)
surface
Area 466.31040554595984
Area 466.31040554595984
Area 10000.0
Area 466.31040554595984
Area 10000.0
Area 466.31040554595984

 

[Danielm103]

something like this (AI generated)

 

;;; =========================================================================
;;; AutoLISP ACIS/SAT Geometric Decoder Script - Print to Screen
;;; Decodes scrambled DXF groups 1 and 3 data and prints it to the command line
;;; =========================================================================

(defun c:DecodeSatPrint ( / ent enx dxfPair strBytes itm lin cha decodedStr)
  (vl-load-com)
  
  ;; 1. User prompts to select a valid 3D Solid or Region
  (setq ent (car (entsel "\nSelect 3D Solid or Region to decode: ")))
  
  (if ent
    (progn
      (setq enx (entget ent))
      
      ;; Verify if the entity type actually holds ACIS data
      (if (member (cdr (assoc 0 enx)) '("3DSOLID" "REGION" "SURFACE" "BODY"))
        (progn
          (princ "\n--- START OF DECODED ACIS SAT DATA ---\n")
          
          ;; 2. Parse and Loop through DXF group codes 1 and 3 
          (while (setq dxfPair (car enx))
            (if (member (car dxfPair) '(1 3))
              (progn
                ;; Convert string to ASCII character byte-list and reverse it
                (setq strBytes (reverse (vl-string->list (cdr dxfPair)))
                      itm nil
                      lin nil)
                
                ;; Rebuild scrambled bytes using standard bitwise operators
                (while strBytes
                  (setq cha (car strBytes)
                        strBytes (cdr strBytes))
                  (cond 
                    ((= cha 95)) ;; Skip formatting delimiters
                    ((= cha 86)  (setq itm (cons 73 itm)))
                    ((= cha 32)  (setq lin (cons (if itm (vl-list->string itm) "") lin) itm nil))
                    ((boole 6 cha 95) (setq itm (cons (boole 6 cha 95) itm)))
                  )
                )
                
                ;; Print structural line streams directly to the command line
                (setq decodedStr (vl-list->string itm))
                (if (/= decodedStr "")
                  (princ (strcat decodedStr "\n"))
                )
              )
            )
            (setq enx (cdr enx))
          )
          
          (princ "--- END OF DECODED ACIS SAT DATA ---\n")
          (princ "\nTip: Press F2 to open the AutoCAD Text Window to copy the full log.")
        )
        (princ "\nError: Selected entity does not contain ACIS geometry data.")
      )
    )
  )
  (princ)
)

(princ "\nACIS SAT Decoder (Print version) Loaded. Type 'DecodeSatPrint' to execute.")
(princ)

 

asmheader
body
lump
transform
shell
face
face
loop
plane-surface
face
loop
plane-surface
coedge
face
loop
plane-surface
coedge
coedge
coedge
coedge
edge

 

I'd bet you could make AI make a mini brep for lisp