Arc Polyline Disaster

[jbrhwy]

How VW handles arc polylines must be addressed, it is unacceptable that the software can change the radius of an arc vertex without providing any WARNING. The attached file "Arc Polyline Disaster.vwx" illustrates the condition.

Since I have been reporting this problem for 15 years & neither Nemetschek or Graphsoft have been unable to address it, I want everyone who uses arc polylines to be aware of the problem.

This problem has also been confirmed in Vw2009 by Michael Young.

[M.CH]

If you place an additional vertex at the end of the 80m arc, it will no longer experience changing behaviour.

[jbrhwy]

Why should you have to place an additional (corner) vertex. When you do add a corner vertex to the polyline the radius can not be increased & in addition the polyline will not offset correctly.

[Ray Libby]

How are you doing this? I just used the fillet tool and it worked fine.

[jbrhwy]

Ray

The OIP was used to change the corner vertex to an arc vertex. For road & railway design curves are applied to the intersection of tangents.

You are correct, but you can not change the radius now because 4 additional corner vertexes were added by Vw & in addition the polyline can not be offset correctly without regressively adding & deleting corner vertexes.

The continuing saga is that I need the ability to edit arc polylines, what is required is an additional vertex mode that places an arc radius at the intersection point without any phantom midpoint.

Thanks for looking at the example.

[Ray Libby]

How do you do that? I don't see that option in the OIP.

[jbrhwy]

Ray

In some versions of Vw "A" shows as a polygon but it started as a polyline, as a polyline the OIP for the 2-D Reshape tool can change the vertexes.

[mike m oz]

Bruce - It becomes a polyline in VW 2009 as well and the same problem exists if you use the 2D Reshape tool. If you apply the curves to the polygon using the 2D Fillet tool both radii end up being correct and they will offset correctly both inwards and outwards.

The problem you are experiencing exists in the change vertex mode of the 2D Reshape tool. It shouldn't do what it does but it always has. When you know that it exists you can deal with it by only applying curves with the 2D Fillet tool. Those that don't know get caught out.

As you pointed out the drawback to the fillet method is it adds vertices at the start and end of each curved segment. It also adds vertices to the arcs at 90?, 180? and 270? (if you decompose the polyline the arcs will be split at these points). If you want to change the curve radius you need to delete these additional vertices first.

One interesting thing I noticed is your 80 m radius curve only redistorts when you delete the additional vertex on the arc. You can delete all the other vertices without it having an impact. Also if you change the poly smoothing back to vertices you can see what the impact of this additional vertex is on the polyline. Perhaps one of the NNA people can explain for you why it works this way.

[Ray Libby]

Got it, thanks, I see what you are talking about.

[jbrhwy]

Mike

If you offset the Vw2008 polyline inside by 10 metres the resulting arc radius is 70.085 (error of 85 mm) not 70 metres (design tolerance is +/- 10 mm), if you offset the resulting polyline another 2.0 metres (ie to get back of sidewalk) the error gets even larger.

In VW12.5 the radius becomes 69.755 (error of 245 mm), this error was fortunately identified at the time of curb & gutter survey layout.

[Ozzie]

The problem you are experiencing exists in the change vertex mode of the 2D Reshape tool. It shouldn't do what it does but it always has. When you know that it exists you can deal with it by only applying curves with the 2D Fillet tool. Those that don't know get caught out.

Again

It shouldn't do what it does but it always has.

If you have what ever it is you wish to offset say by 6 metres - should'nt a user be able to do that without work arounds and hidden understandings

If you went into McDonalds and asked and paid for a Big Mac and drove away to discover you really had a Cheese Burger in most instances what would happen?

I do not think McDonalds would get away with oh sorry those that don't know get caught out

The tool should do it properly or

it is unacceptable that the software can change the radius of an arc vertex without providing any WARNING

Simple

A couple of days back I placed a pad on a site model at a certain height and then used the Stake Object to read heights off the site model - I placed one in the centre of a pad and I think the reading was incorrect but I did not have time to test it

Today I discovered a bug with exporting to my User folder Plant defaults

Last year - 2008 - I discovered several bugs - 12 the same

This issue

I have been reporting this problem for 15 years & neither Nemetschek or Graphsoft have been unable to address it

We all love VW

A couple of weeks back Jeffrey did a great thing with Worksheets - really instructive and very transparent

Cmon NNA - the new parasolids engine

Can it deal with this or not?

[mike m oz]

Bruce - In VW 2009 the curves are offset correctly accurate, as shown in the attached image (dimension precision of 0.001 m).

Ozzie - there will be a logical reason why the vertex mode does what it does.

[jbrhwy]

Mike - could you post the Vw2009 file that you used to create & offset the polyline.

Michael Young had tested my file in Vw2009 & commented "Well, your suspicions are confirmed. I could not leverage v2009 to accomplish this".

Please note the file (Arc Polyline Disaster.vwx) I posted is a very simplified version of the actual design, more curves, no road intersections or driveway curb returns.

What happens when the polyline includes a vertex with an intersection angle greater than 90??

Thanks for your assistance on this matter.

[mike m oz]

Bruce, all I did was duplicate array your polygon and used the 2D Fillet tool to create the two radii on the road centreline. I then used the Offset tool on the resulting polyline to create the kerb and footpath polylines (I didn't delete or move any of the vertices).

If you use the vertex change mode of the 2D reshape tool the problem occurs. If you use the Fillet tool it doesn't. Doing it the latter way you lose some flexibility, but at least the result is correct (true for both VW 2008 and VW 2009).

[jbrhwy]

Mike

When I use the fillet tool & then offset tool in Vw2008 the inside radius is 70.085 metres not 70.000 metres (beyond the required +/- 10 mm tolerance.

Would you go to the next step which is to revise the curve radii because the roadway is too close the right-of-way, change curve 1 radius to 85 metres & curve 2 radius to 25 metres & then do the offsets again. This is the ongoing problem arc polylines can not be easily revised because of the phantom midpoint.

Huge problem for me as 70% of my design work involves polylines.

[mike m oz]

Apologies - I thought it was working in VW 2008, but it isn't. When I did the check I had decomposed the polyline into its individual elements which is why they came out correct. Careless of me.

VW 2009 absolutely does work with the polyline though. The radii are what they should be.

[jbrhwy]

Mike

Were you able to revise radii using OIP or the fillet tool & if you did what were the steps involved? In other versions, sometimes revising radii would change the original point of intersection of the tangent lines (phantom arc vertex).

Thanks for staying with me on this dilemma.

[mike m oz]

Bruce, in VW 2009 adding the curves to the polyline using the fillet tool provides the correct radii, and these will then offset correctly.

In the example shown in the first image below I took your original polyline and extended the length of the first segment to match the length of the second segment. I then duplicated it, rotated it through 90 degrees and then matched it to the original polyline so I could compose them into a single continuous poly line. This formed the centreline (dot-dashed) line and after applying the 80 m and 20 m fillets I offset it inwards and outwards by 10 m, 2 m and 4 m. All of the radii dimension as what they should be.

I then duplicated the centreline poly and decomposed it. The various segments have been colour coded to show what happened. Where arc segments cross the 90?, 180? and 270? axes the arcs get split. Why they need to do this I don't know, nor why they don't split at the 0? axis.

I think you will just have to accept that changing the arc vertex radii by the OIP is problematic and doesn't always produce the correct result because of the way the curves seem to interact with each other.

If you set out your road centrelines and then apply the curves using the fillet tool though your offset curves will be reliable in VW 2009.

[jbrhwy]

Mike

Would you test one last item, what happens when the polyline includes a vertex with an intersection angle greater than 90? & the tangent of the radius is greater than 1/2 the distance between the points of intersection?