I have two 3DPolylines in 3D space that run roughly parallel but with variable offset between them. I need to generate a third 3DPolyline representing the central axis between both. Is this possible using LISP? Any suggestions or sample routines are welcome.
The attached image shows two parallel 3DPolylines with non-uniform spacing. The goal is to generate a central 3DPolyline equidistant (or interpolated) between them along their entire length.
If there’s the same number of vertices on each polyline, then you can build a new polyline from the mid points. I have no idea how to do this in lisp, but maybe this will give a hint
import traceback
from pyrx import Ap, Ax, Db, Ed, Ge, Gi
@Ap.Command()
def doit():
try:
db = Db.curDb()
ps, id1, _ = Ed.Editor.entSel("\nPick p1", Db.Polyline3d.desc())
ps, id2, _ = Ed.Editor.entSel("\nPick p2", Db.Polyline3d.desc())
pl1 = Db.Polyline3d(id1)
pl2 = Db.Polyline3d(id2)
vtxids1 = pl1.vertexIds()
vtxids2 = pl2.vertexIds()
if len(vtxids1) != len(vtxids2):
return
pnts = []
for vid1, vid2 in zip(vtxids1,vtxids2):
v1 = Db.Polyline3dVertex(vid1)
v2 = Db.Polyline3dVertex(vid2)
seg = Ge.LineSeg3d(v1.position(),v2.position())
pnts.append(seg.midPoint())
pl3 = Db.Polyline3d(Db.Poly3dType.k3dSimplePoly,pnts,pl1.isClosed())
db.addToCurrentspace(pl3)
print("\nWooHoo!")
except Exception as err:
traceback.print_exception(err)
Here's another AutoLisp approach [lightly tested]:
(defun C:3DPMID (/ pl1 pl2 o1 o2 co1 co2)
(setq
pl1 (car (entsel "\nFirst 3D Polyline: "))
pl2 (car (entsel "\nSecond 3D Polyline: "))
); setq
(if
;; [correct object types, same number of segments, &
;; either both closed or both open]
(and
(=
(cdr (assoc 100 (reverse (entget pl1))))
(cdr (assoc 100 (reverse (entget pl1))))
"AcDb3dPolyline"
); =
(= (vlax-curve-getEndParam pl1) (vlax-curve-getEndParam pl2))
(= (vlax-curve-isClosed pl1) (vlax-curve-isClosed pl1))
); and
(progn ; then
(setq
o1 (vlax-ename->vla-object pl1)
o2 (vlax-ename->vla-object pl2)
co1 (vlax-get o1 'Coordinates)
co2 (vlax-get o2 'Coordinates)
); setq
(command "_.copy" pl1 "" '(0 0 0) '(0 0 0)); a copy to get new Coordinates
(vlax-put
(vlax-ename->vla-object (entlast))
'Coordinates (mapcar '(lambda (x y) (/ (+ x y) 2)) co1 co2)
); vlax-put
); progn
); if
(prin1)
)The actual work of it is just the second half -- kind of short and sweet. The first half is all just selection and verifying the right match of characteristics.
If the two selected 3DPolylines are not the same in all properties [Layer, linetype, color, etc.], the mid-path result with have those of the first one selected.
[It could have a prompt added to scold the User if the appropriate characteristics don't match.]
@rsalastopografia wrote:
I changed the 3dpoly Lisp code to polyline ... but it doesn't run correctly. ....
"[I]t doesn't run correctly" is never enough information. What does it do differently from what you expect?
If by that change you mean you changed "AcDb3dPolyline" to "AcDbPolyline" [which will accept only "lightweight" Polylines], that works for me. If you changed it to "AcDb2dPolyline" ["heavy" but planar], that also works for me. But in both cases, if the two are not at the same elevation, the result is at the elevation of the first one. Listing its VLA Properties, it has the Elevation property of that one, but the Coordinates property in the "heavy" 2D version has the every-third-element Z coordinates correctly at halfway between those of the originals. So I guess the Elevation property overrides the Z coordinates of the individual vertices, and stands in place of the Z coordinates in a LWPolyline, so it's necessary to change that Elevation property, too. But I'm not sure what should happen if they are not in parallel planes -- halfway between vertex by vertex is probably not possible except with a 3DPolyline.
@rsalastopografia wrote:
....I changed the code (3dpoly to 2d polyline) but it didn't work as expected.....
Again, "it didn't work" is not enough information. What did it do differently from what you expect?
If you changed it to "2d polyline" with that space, that would not work. Show us the change you made.
For a Polyline, you would probably need to set the elevation to the Z value of one of the vertices. An issue is that the original polylines have a slope. Trying to compute a transformation matrix in lisp is like trying to drive a F150 with a toilet bowl plunger as the gear shift. Maybe a min, max or average Z is good enough. This sample uses max to illustrate the issue
.Command()
def doit():
try:
db = Db.curDb()
ps, id1, _ = Ed.Editor.entSel("\nPick p1", Db.Polyline3d.desc())
ps, id2, _ = Ed.Editor.entSel("\nPick p2", Db.Polyline3d.desc())
pl1 = Db.Polyline3d(id1)
pl2 = Db.Polyline3d(id2)
vtxids1 = pl1.vertexIds()
vtxids2 = pl2.vertexIds()
if len(vtxids1) != len(vtxids2):
return
pnts = []
for vid1, vid2 in zip(vtxids1,vtxids2):
v1 = Db.Polyline3dVertex(vid1)
v2 = Db.Polyline3dVertex(vid2)
seg = Ge.LineSeg3d(v1.position(),v2.position())
pnts.append(seg.midPoint())
z = 0
for p in pnts:
z = max(z,p.z)
pl3 = Db.Polyline(pnts)
pl3.setElevation(z)
db.addToCurrentspace(pl3)
print("\nWooHoo!")
except Exception as err:
traceback.print_exception(err)
