Select.acSelectionSetCrossing problem...

Dear all,

As some of you noticed before, and it goes way back to R14, ACAD's
Select.acSelectionSetCrossing (or by Fence, Point, Window, Polygon, etc.)
doesn't return a valid selection set if given fence points are not VISIBLE
on the screen (whoah!)... Is there any VBA/LISP solution to it? I'm using
huge (but really huge) drawings of some 20 Mbs (of vector data) and
performing a ThisDrawing.ZoomExtents before any mentioned Select is merely
painful experience. Will it be of any help if I use VLAX class and
EvaluateLispExpression for one line getting DXF codes of it's EndPoint
vertex, in a way to get other point's StartPoint vertex?

Regards,
Maksim Sestic

 

Just an idea....

Why not draw a temporary entity using the fence points as vertice's, get
the bounding boxof the new entity, zoom window, using the bounding box
coords, zoom out .9 to make sure everything's seen, delete the temp
entity, do your selection. May not be the best, but it would be faster
than a regen.

Jeff

 

Jeff,

The point of it all is that we are making our own network topology functions
(as Autodesk Map's doesn't work well here and there, and it's expensive
after all) so we need to detect what lines containing specific XData are
adjecent. There is between 2000 and 10.000 lines, so zooming around is out
of question for the sake of user's health Anyway, thanks fro the tip, we
already tried that approach and it just takes too much time.

Regards,
Maksim Sestic

 

OK, I've got another idea which you may have already tried, too.

Create a temp. pline at the location of the fence; create a selection
set of all drawing entities, but filtering for only those you want to
work with (layers, lines, arcs); step through the ss and perform an
"Intersectwith" on each one, with the temp. pline being the test object;
check the xdata for a match; place the entity in a seperate ss if it
matches; use the new ss as required......

I just tried this in a drawing with around 15k lines, plus other
entities, and it found the7 lines I was interested in no time at
all.....

Good Luck,
Jeff

 

Graphical selection methods are not usable for
doing topological classification, but that's a
common misconception.

Graphical methods like fence, window/crossing
operate on the display representation of entities,
not on their mathematical definition. Hence, the
result can be influenced by display magnification,
as well as VIEWRES tesselletion (e.g., circles are
drawn as a chain of short line segments, where the
viewres setting determines the granularity of the
tessellation).

In fact, graphical selection is only accurate to
one display pixel (or possibly a virtual display
coordinate), so that means that you can zoom out
far enough to cause a line that is close to, but
not actually contained by a boundary to be selected
by a fence derived from the boundary.

Topological classification requires much more than
that. You have to use analytical methods, such as
a combination of intersection and point containment
testing, line itegrals, the winding algorithim, etc.



AcadX for AutoCAD 2004 Beta 1
http://mysite.verizon.net/~vze2vjds/acadx/AcadX16.zip

 

Tony,

I'm aware of common methods used in topological operations, but this one we
are trying to implement is based on developing a simple 2D network topology.
Basic ACAD's platform Map phylosophy relies on is "unreliable" for designing
such networks - the problem lies in it's concept of holding and representing
data, not to mention developed drawing tools (based on that concept). What
happens at the common user who used to draw a network topology "by hand" (in
analog form)? Well, it takes _a lot_ of training (snap here, snap there) and
time (clean up the drawing, regenerate the network) to complete one simple
task. It's a way different concept than the one Autodesk commercially
propagates, it's more "CAD-based" and much less
"Digitize-Topographic-Map-And-Generate-Network-Topology" one.

Having that in mind, we designed simple tools for generating 2D network
topology by drafting, "in one sweep" (with very limited use, though). As I'm
dealing with infrastructure planning and design, I also had to design stable
object (feature) classes and methodologies to support such classes in
various ways. The final result is relatively simple but functional model of
an infrastructure network that acts like a "real one". The only difference
is that it runs on plain AutoCAD.

Back to the current problem Basically, I'm trying to detect a "crossing"
of two (or more) lines by investigating the endpoint of one line. If there
is more than one adjecent line to inspected one, then it's a crossing. Funny
thing is that two lines, one touching another (using OSNAP), do not have the
same X and Y startpoint/endpoint. They differ somehow - say, DXF group code
11 (End point (in WCS)) of one line and group code 10 (Start point (in WCS))
of the other _are not the same_, so I just can't use selection set filters
to detect the "crossing". Is there any solution to it?

Regards,
Maksim Sestic

 

Jeff,

The problem still remains - you just can't inspect SelectByIntersection
selset if it's "out of visible part of the drawing". The result is
(generally) empty selection set.

Regards,
Maksim Sestic

 

Maksim,
I think you missed my point. I wasn't suggesting SelectByIntersection at
all. I'm saying get ALL lines (or arcs, or polylines) on certain layers.
Create a polyline using the "fence" points as the vertex data. Inspect
each entity in the selection set to see if it intersects the polyline,
if it does, place THAT into a new selection set.

This does work for items outside the visible area.....

Here's what I used to test with in drawing who's "status" shows:
48441 objects in F:\99\111 - Brennan Acres\master.dwg
Model space limits are X: 0.00 Y: 0.00 (Off)
X: 1080.00 Y: 720.00
Model space uses X: -8961.28 Y: -235.67 **Over
X: 7242.35 Y: 2067.91 **Over
Display shows X: -19658.04 Y: -9313.40
X: 17019.14 Y: 8375.13
Insertion base is X: 328.64 Y: 1819.93 Z: 0.00
Snap resolution is X: 1.00 Y: 1.00
Grid spacing is X: 0.00 Y: 0.00

Current space: Model space
Current layout: Model
**********************************************
Sub testXing()
Dim ss As AcadSelectionSet
Dim newSS As AcadSelectionSet
Dim dxfCode(1) As Integer
Dim dxfVal(1) As Variant
Dim objEnt As AcadEntity
Dim objLine As AcadLine
Dim fence(5) As Double
Dim pickPt As Variant
Dim fenLine As AcadLWPolyline
Dim Util As AcadUtility
Dim i As Long

Set Util = ThisDrawing.Utility
dxfCode(0) = 0: dxfCode(1) = 8
dxfVal(0) = "LINE": dxfVal(1) = "EGSRF-VIEW"
On Error Resume Next
Set ss = ThisDrawing.SelectionSets.Add("fences")
If Err.Number <> 0 Then
Err.Clear
Set ss = ThisDrawing.SelectionSets.Item("fences")
End If
Set newSS = ThisDrawing.SelectionSets.Add("newss")
If Err.Number <> 0 Then
Err.Clear
Set newSS = ThisDrawing.SelectionSets.Item("newss")
End If
On Error GoTo 0
ss.Clear
newSS.Clear
ss.Select acSelectionSetAll, , , dxfCode, dxfVal

fence(0) = -8560#: fence(1) = 1038#
fence(2) = -1296#: fence(3) = 740#
fence(4) = 5417: fence(5) = 1223#

Set fenLine = ThisDrawing.ModelSpace.AddLightWeightPolyline(fence)
For Each objEnt In ss
Dim varInters As Variant
Dim entSS(0) As AcadEntity
varInters = objEnt.IntersectWith(fenLine, acExtendNone)
If UBound(varInters) > 0 Then
Set entSS(0) = objEnt
newSS.AddItems (entSS)
End If
Next
newSS.Highlight True
fenLine.Delete
End Sub
****************************************
Afterwards, using a little lisp, my "newss" shows it has entities in it:
(setq ss (vla-item (vla-get-selectionsets *doc*) "newss"))
(vla-get-count ss)
394
I can replicate this no matter where I'm zoomed to in the drawing....

HTH,
Jeff

 

It looks like you didn't read what I said.

You can't use selection set methods to do what
you want. They're only accurate to a pixel, and
they don't work on objects outside of the view.



AcadX for AutoCAD 2004 Beta 1
http://mysite.verizon.net/~vze2vjds/acadx/AcadX16.zip

 

Tony,

I solved a problem using VLAX class to obtain inspected line's
strapoint/endpoint, and then selecting _all_ entities (equivalent to X
switch used by LISP) while filtering it for DXF codes 10 <OR> 11 and <XOR>
inspected entity's handle. I needed a set of all lines starting/ending at
the endpoint of inspected line ("crossing").

Regards,
Maksim Sestic