line-weight Posted October 4, 2019 Share Posted October 4, 2019 (edited) Easiest to explain this by providing an example of what I'm trying to do. I've got two bridges, and I want to draw the wall of a viaduct that runs on a curve between them. I know the path of the wall in plan, so I draw the NURBS curve, all on the X-Y plane: Then I use this NURBS curve as the path for an Extrude-along-path, to create the wall: That's fine except that the bridge on the left is at a higher level than the bridge on the right, so the base of the wall where it meets the bridge on the left is too low: I can fix this by editing that NURBS curve, and raising the Z value of some of its vertices towards that end: And that in principle gives me what I want. However - ideally what I want is a smooth gradient from one end of the curved wall to the other. That's not what I've got, as can be seen looking at the wall in orthogonal elevation: Obviously I can improve that, just by fiddling manually with the Z-values of each of the vertices of the path, but that's rather tedious and I'll only get it as good as I can manage by eye. Is there some way to draw that NURBS curve, such that I can make it follow a constant gradient from one end to the other? Edited October 4, 2019 by line-weight Quote Link to comment
EAlexander Posted October 4, 2019 Share Posted October 4, 2019 Two ideas come to mind: You could create it as a loft with three profiles: start finish and middle. You can use align distribute to get the middle centered truly between the start and end profiles. Or you could use sweep (assuming a constant radius and adjust the pitch value to get the rise. e. Quote Link to comment
markdd Posted October 4, 2019 Share Posted October 4, 2019 Yes, I think so. If you create a working plane that spans the two levels, then draw or edit your nurbs curve vertices using the working plane as your Z=0 reference. Working Plane and Nurbs curve.vwx 1 Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 12 minutes ago, EAlexander said: Two ideas come to mind: You could create it as a loft with three profiles: start finish and middle. You can use align distribute to get the middle centered truly between the start and end profiles. Or you could use sweep (assuming a constant radius and adjust the pitch value to get the rise. e. Unfortunately it's not following a constant radius ... it's following a path that I will trace off a survey plan. So I don't think a sweep would work. I don't think a loft would work either, for the same reason - the true line of the curve can't be interpolated just from 3 points. Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 14 minutes ago, markdd said: Yes, I think so. If you create a working plane that spans the two levels, then draw or edit your nurbs curve vertices using the working plane as your Z=0 reference. Working Plane and Nurbs curve.vwx That might give a near-enough-right result ... but wouldn't be geometrically correct in terms of a constant gradient along the path, because of the curve in plan (the gradient would be steeper in the middle than at each end). I think. Quote Link to comment
markdd Posted October 4, 2019 Share Posted October 4, 2019 Try offsetting the curve to make a 2nd Rail curve and use the Loft Surface command (3rd mode) instead? I think I've achieved what you are looking for?! Working Plane and Nurbs curve.vwx Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 Unfortunately I'm on 2018 here so can't open your example file... Quote Link to comment
zoomer Posted October 4, 2019 Share Posted October 4, 2019 Doesn’t it work with Profiles + Rail mode ? Quote Link to comment
markdd Posted October 4, 2019 Share Posted October 4, 2019 Here it is in 2018 Working Plane and Nurbs curve v2018.vwx Quote Link to comment
zoomer Posted October 4, 2019 Share Posted October 4, 2019 (edited) http://app-help.vectorworks.net/2019/eng/index.htm#t=VW2019_Guide%2FShapes2%2FCreating_a_Loft_Surface.htm%23XREF_15316_Creating_a_Loft Bi-Rail Sweep. Where 2 Lines at both ends define Wall heights and the Nurbs Curve is used as „Profile“. And finally thicken that Surface, to get a 3D Wall. Edited October 4, 2019 by zoomer 1 Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 15 minutes ago, markdd said: Here it is in 2018 Working Plane and Nurbs curve v2018.vwx Thanks - but that has the same issue - the gradient of the curve is not constant, measured along the curve. To make the extreme example - I've drawn the large arc on the same working plane as your S-curve, but the top bit of that arc is not going to be on a downward gradient (in fact it will go slightly uphill at the start). Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 17 minutes ago, zoomer said: http://app-help.vectorworks.net/2019/eng/index.htm#t=VW2019_Guide%2FShapes2%2FCreating_a_Loft_Surface.htm%23XREF_15316_Creating_a_Loft Bi-Rail Sweep. Where 2 Lines at both ends define Wall heights and the Nurbs Curve is used as „Profile“. And finally thicken that Surface, to get a 3D Wall. Do you mean like this (the lines highlighted in orange are the two 'rails', the wavy line is the profile) When I try and perform a birail sweep, it will let me select the two lines but not the profile. Quote Link to comment
zoomer Posted October 4, 2019 Share Posted October 4, 2019 (edited) I think the Lines (everything) need to be converted to NURBS first ? Yes, works for me. - Created 2 Vertical Lines - Modify > convert to Nurbs - Created a horizontal Nurbs Curve - Loft Object Select 1. Line 1 2. Line 2 3. Curve 4. (I activated Solid Mode) 5. Accept - Shell Object Edited October 4, 2019 by zoomer Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 Ok. Got it to work after some fiddling. Being fussy though - when I look at in orthogonal elevation, I can tell the gradient isn't constant because it actually goes upwards very briefly around the middle. In both of the variants below. Maybe this is something that would disappear if the NURBS curve had more control points? Quote Link to comment
line-weight Posted October 4, 2019 Author Share Posted October 4, 2019 (edited) Hrm. Here is what happens with a more complex curve. It's pretty clear it's not giving me a constant gradient. The top image is an elevational view. *Edit - ignore this post! I messed up by accidentally not drawing my curve on one plane. Hence the bottom is not flat. Edited October 7, 2019 by line-weight Quote Link to comment
zoomer Posted October 4, 2019 Share Posted October 4, 2019 I had indeed more control points when painting something NURBSy onto my Roof 🙂 But I wasn't aware that your Bridge bases have a slope. Thought they had just different heights. I think in that case, with that Tool usage, you would need to adapt your Path in Z. So I would do it with as few control points as possible. Or in case it does not matter when the Wall extends into the terrain, just start at the lowest level and add it to the Walls end height. I have already thrown the test file away but AFAIK the top slope looked pretty linear for me. Quote Link to comment
line-weight Posted October 7, 2019 Author Share Posted October 7, 2019 On 10/4/2019 at 8:54 PM, zoomer said: But I wasn't aware that your Bridge bases have a slope. Thought they had just different heights. Actually I have edited the post above - it was my mistake, the base was not supposed to have a slope. Quote Link to comment
line-weight Posted October 7, 2019 Author Share Posted October 7, 2019 However: here I think is proof that the loft tool unfortunately can't do what I want. The extruded squares are a duplicate array, so the distance between them is equal. The NURBS curve that will become the 'profile curve' is drawn with control points on each of the bottom corners of the extrudes, as shown. So the distances between control points are equal. The extrudes step down in height by an equal amount. So if the 'top slope' of my loft object is to have a constant gradient then it should be passing exactly through the top corner of each of the extrudes. But this is what happens: There are actually two problems: 1. The gradient is not constant 2. The top line is not directly above the base line...in other words, if it is a wall then it is leaning over. Quote Link to comment
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