Precision placement of 3D objects

[P Retondo]

Tom, you are probably not missing anything, but there are workarounds for your problem. There are many ways to do it, but I don't have any particularly clever suggestions. For example, you can take a 3D section of an object through its center, group that with the original object, and have some corners to grab that coincide with the original object's center. You can also use Working Planes to give you an orientation where 2D objects can be created to overlay the 3D stuff, and their snap points can then be of help for moves constrained to the working plane orientation (in other words, like this - draw a polygon or polygons the shape of your objects, move the polygon using a center point grip to the desired location, then move the 3D object to one of the corners of the polygon. This move will be a 2D move constrained to the i,j system.)

You can probably figure out better ways on your own. One detail you might be missing - the cursor turns to a hollow triangle when snapping to an object edge. You just can't control where on that edge you are, except at the vertices.

I haven't worked with NURBS enough to know if there is any advantage to converting your object to NURBS - maybe someone more familiar with that area could help.

This would be a great wish list suggestion - to have a handle added at the center of every 3D object edge. Mathematically it would be quite simple, although on the other hand it might slow down VW performance.

[ 09-27-2003, 04:29 PM: Message edited by: P Retondo ]

[Turboman]

Hi,

I've been using VW for 2D mechanical design work for some time and am very pleased with the results. I've recently begun trying to build 3D models of a machine I've developed and am running into some problems...perhaps due to my ignorance. I'm presently running VW 9.5.3 Mechanical on Mac OS 10.2.5.

My problem is this;

In 2D, it is easy to locate objects with high precision with respect to part edges by editing object coordinate values in the Object Info palette.

However, I have not found a similar capability in the 3D workspace. 3D coordinates are not provided in the Object Info pallete. Nor do Smart Cursor cues seem available for picking up edges and centers. Short of dragging and/or moving, I cannot find another way to locate 3D parts precisely. (Any precision move MUST be made with respect to an edge or center of the part.) I've figured out how to make some nice looking 3D shapes, but due to lack of control over precision, these cannot be used for engineering purposes.

If this cannot be done within VW, then VW is not the right program for what I need to do.

Am I missing something here?

Thank you for your help.

Tom

[Bart Rammeloo]

He is actually missing something. Check out http://www.nemetschek.net/3dpowerpack/features.html and look for improved 3d object snapping. combine this with the move 3D command, and presto! Don't forget there's also this thing called working planes - they too have been improved in 10.5.

Cheers,

BaRa

[Turboman]

P/BaRa,

Many thanks for the quick reply. It "appears" that v.10.5 includes smart cursor functionality as in 2D.

What I was thinking of was the ability to view the object from the +x,+y or +z directions and then have the smart cursor provide 2D moves in constant x,y,z planes respectively...perhaps same approach also for working planes for manipulating non-orthogonal parts/assemblies.

Can anyone here explain how well the new 3D smart cursor fucntionality actually works?

I still can't even export to DXF format after months of Tech Support "assistance", so am skeptical about NNA's marketing claims. ;(

Best regards,

Tom

[RonR]

I have been trying to do precise 3D work in VW, in my case with little CAD experience, also on a Mac (under OSX 10.2.7). I've found that it is generally possible (and I have been dealing with extremely complex and irregular shapes). I've had to learn the limitations of each object type and plan ahead in the process of doing the drawing. In the process I have been down quite a few blind alleys. The examples and tutorials are a bit basic and don't address the overall strategy for creating complex 3D designs. Vector Works is easy to start using, and easy in 2D design, but there are a lot of capabilities that have not been so easy to figure out- my assumption is that someone with more 3D experience would have an easier time.

Things that have helped me:

Extensive use of the "Edit Group" command allows you to regress to an earlier phase and change objects precisely, while maintaining their position in the drawing.

Snapping the working plane to an object surface and aligning other objects with reference to the working plane.

Placing a 3D locus and aligning the objects to the locus.

In some situations precise alignment is possible using the align 3D command- it depends on what part of the object you are trying to align.

The very recent update to VW (10.5) has been incredibly useful, particularly the improved snap 3D and most particularly the NURBS analysis tool. This latter allows you to query the relative position of NURBS lines and surfaces and place lines or loci at intersections or at the nearest points. I've used this to precisely fair complex curved shapes.

I don't completely remember details of version 9, but the latest versions have much greater capability in 3D mechanical design. I feel the upgrades have been well worth it.

I still am a little unclear about how to get two NURBS curves to intersect reliably (as in using them to Create Surface from Curves). I can position the vertex of both lines with the keyboard at the same position to the level of precision specified for the drawing, but still not have them intersect. If anyone can clue me in I'd appreciate it.

Good luck.

RonR

[Bart Rammeloo]

Hi RonR,

Thanks for the tip about the NURBS analysis tool. It never occured to me to use it for simple distance evaluation between simple geometry - I always had complicated NURBS geometry in mind, and couldn't actually imagine what it was good for. Thanks again

Cheers,

BaRa

[Turboman]

Ron,

Thanks so much for the excellent tips on precision 3D modeling in VW. You've convinced me to fork out the $$ for the upgrade to v10.5.

However, what little I've done with NURBS in v9.5 leaves me less than satisfied. For example, I need to loft a precise airfoil surface using 2 or more section profiles originally entered as 2D loci. While the 2D "compose curve" command does an acceptable job converting the loci to smooth curves, the subsequent "convert to NURBS" (required for lofting the 3D surface) introduces too much distortion.

How might one go about this in 10.5 to obtain an accurate NURBS airfoil profile from a 2D locus? Please note that the airfoil has a nonuniform chord length, so a simple "extrude" or "tapered extrude" command will not work.

Thanks again for your help.

Best regards,

Tom

[Biplab]

Ron R wrote:

"I still am a little unclear about how to get two NURBS curves to intersect reliably (as in using them to Create Surface from Curves). I can position the vertex of both lines with the keyboard at the same position to the level of precision specified for the drawing, but still not have them intersect. If anyone can clue me in I'd appreciate it."

I think the way to create intersecting curves is to use the new 3D snapping features available in VW10.5. Let's say you have the curves flowing in the U-direction. And you are now creating curves that flow in the V-direction. Using the NURBS tool when you create these curves you can snap to the U-curves at any point on the curve. On the curves you can snap to any point on the curve, the control points/fit points and to the center if it's a circular curve.

[Biplab]

Tom wrote:

"However, what little I've done with NURBS in v9.5 leaves me less than satisfied. For example, I need to loft a precise airfoil surface using 2 or more section profiles originally entered as 2D loci. While the 2D "compose curve" command does an acceptable job converting the loci to smooth curves, the subsequent "convert to NURBS" (required for lofting the 3D surface) introduces too much distortion.

How might one go about this in 10.5 to obtain an accurate NURBS airfoil profile from a 2D locus? Please note that the airfoil has a nonuniform chord length, so a simple "extrude" or "tapered extrude" command will not work."

If I understand the problem correctly, you are probably joining the 2D loci with linear segments and then composing them. You cannot just compose 2D loci. And then you are converting the resulting polyline into NURBS curve using Convert To NURBS. You might also want to use the NURBS curve tool with the "Fit Points" mode, and click on the 2D loci to create the NURBS curve directly.

Sorry if I misunderstood the question.

[Turboman]

Dear Moderator,

You are correct. I originally generated the airfoil profiles for 2D use only, so NURBS was not an absolute requirement.

I'm not familiar with the NURBS "fit points" command. Is this available in v9.5 or must I upgrade to 10.5?

Best regards,

Tom

[Biplab]

What I mean by "Fit Points" is - use the NURBS curve tool in the default mode (NURBS curve by interpolation points) mode. The other mode is NURBS curve by control points mode. Using interpolation points mode, the NURBS curve passes thru the points clicked.

[Turboman]

Dear Moderator,

If the observed surface irregularity is merely a screen resolution type issue and not a representation of the underlying mathematical model, then that's what I needed to know.

Many thanks!!

Best regards,

Tom

[Turboman]

Dear Moderator,

Understood. I will do as you suggest and see what happens.

Since I've recently started working in 3D, there's probably a lot of tricks I need to learn.

One of the things I've noticed when converting extruded 3D shapes to NURBS surfaces is that the extruded surface of the 3D part appears to become somewhat irregular. While this might be okay for "art work", it isn't going to cut it if your objective is to generate a 3D model for export to a CNC g-code generating CAM package...which is MY objective.

As such, I'm still a bit concerned about loss of precision when converting from precise 2D geometry to 3D NURBS geometry in VW. Going back into the 3D model and manually tweaking control points isn't going to cut it.

Are my concerns justified?

Best regards,

Tom

[Biplab]

I would say that your concerns are not justified. The model in VectorWorks is stored with precision similar to any other production quality CAD program. The surface may appear "irregular" as you say - but the internal geometry stored is quite high quality. You can control the visual aspect by changing 3D conversion resolution from low to high or very high in the VectorWorks preferences. And even if the visual aspect is coarse, the snapping mechanism, and other functionality still works with the exact model.

[RonR]

re. Turboman, "I need to loft a precise airfoil surface using 2 or more section profiles originally entered as 2D loci. While the 2D "compose curve" command does an acceptable job converting the loci to smooth curves, the subsequent "convert to NURBS" (required for lofting the 3D surface) introduces too much distortion.'

I have been generating complex curved 3D shapes by drawing 2D cross sections, converrting them to NURBS, moving them in 3D to the appropriate seperation, and using the lofting tool to generate the shape. The lofting tool does not require the intersecting curves. Compose curves has worked well in some situations, but for the airfoil shape you are describing I suspect the lofting might be easier.

For some irregular shapes I needed to fair I placed a NURBS planar surface at various points intersecting the curves, used the NURBS analisis tool to place a locus at the intersections, then drew a NURBS curve that snapped to the loci. This seemed to show up any distortions in the shape before using the lofting tool, so I could adjust the curves precisely using keyboard commands to move individual vertex points.

As has been mentioned, the irregularity you see in the display is the 3D conversion resolution, not the actual data. I put my conversion settings up high for smoother display since I got the new G5 Mac- the performance reports for this system on the NNA site are, if anything, understated. A render I did for comparison took 4.5 minutes on my old G4-500 mz, on the G5 1.8 single processor it was done in just over ten seconds. And it's quiet, too. Now I'm glad waited so long to upgrade.

RonR