Any idea why Curve.Offset (2) offsetting Z on two of the lines but not the others?
In Element.Curves (1) ALL the Z coords are 0 and all the Z vectors are 0
Iâve no idea to why it does that!
Probaby @GavinCrump can help us out since I feel he is really good when it comes to geometry.
But in case if you want the desired output, you can flatten your list before it enters the PolyCurve node.
3 Likes
Thanks!
I swapped my normal lines for a boundary line in Revit and that worked too.
Still would like to know though if anyone has an idea 
The curves are offset within their existing plane. Some of the elements you pulled curves from were not in the XY plane.
1 Like
I donât understand.
All Z numbers were 0 so doesnât that make them in the XY plane only?
I took the elements from a rectangle (detail lines) in Revit all at the same Z coordinate which was zero.
Best way to learn this is to break this down into reality worldâ examples.
Almost all geometry in Revit is based on a work plane as the âhostâ. The plane could be a level, a view, a grid, a reference plane, or the face of an existing piece of geometry. Your geometry then has a coordinate system based on that plane.
- Take a piece of paper and lay it flat on the table.
- Now draw an X and a Y axis on the paper. The âzâ axis will be âout of the pageâ where they meet.
- Next draw a line anywhere on the page. This is how Revit defines the line.
- Now draw an offset line on the page. This is how Dynamo offset the line in 3D space - relative to the XY plane of the page, which is currently parallels to the global XY of the room.
- Now take your paper and pin it to a wall. The offset line now has a Z component in the world space because the paper which hosted both the line and the offset line is no longer parallel to the global XY plane.
2 Likes
OK - but I drew the rectangle using a detail line and a rectangle tool.
How can 2 sides be in a different plane from the other two sides?
[0] Line(StartPoint = Point(X = 15675.147, Y = 11956.953, Z = 0.000), EndPoint = Point(X = 15675.147, Y = -12743.047, Z = 0.000), Direction = Vector(X = 0.000, Y = -24700.000, Z = 0.000, Length = 24700.000))
[1] Line(StartPoint = Point(X = 15675.147, Y = -12743.047, Z = 0.000), EndPoint = Point(X = -12324.853, Y = -12743.047, Z = 0.000), Direction = Vector(X = -28000.000, Y = 0.000, Z = 0.000, Length = 28000.000))
[2] Line(StartPoint = Point(X = -12324.853, Y = -12743.047, Z = 0.000), EndPoint = Point(X = -12324.853, Y = 11956.953, Z = 0.000), Direction = Vector(X = 0.000, Y = 24700.000, Z = 0.000, Length = 24700.000))
[3] Line(StartPoint = Point(X = -12324.853, Y = 11956.953, Z = 0.000), EndPoint = Point(X = 15675.147, Y = 11956.953, Z = 0.000), Direction = Vector(X = 28000.000, Y = 0.000, Z = 0.000, Length = 28000.000))
The lines are on the same plane surely?
What am I missing?
To follow @jacob.smallâs paper analogyâŚ
If the paper represents the local XY Plane and the table represents the global XY Plane (Z=0), then holding the paper 6" off the table does not mean that the paper is no longer an XY Plane. It just means that the local XY Plane now has a Z coordinate of 6.
OK. I understand that. But surely the lines drawn using the rectangle tool in Revit all have the same Z plane?
So why do two of them offset on the Z plane but the other two donât?
Was the rectangle drawn in a drafting view?
All this isnât to say that something weird isnât going on. It does seem odd that a rectangle drawn in a view would put lines on different local planes. But logically there are reasons this could happen.
I would expect a rectangle in a drafting view to be on the same plane. A model view could be different. Iâm guessing that the normal plane for each curve varies based on the direction itâs drawn.
The original rectangle in Revit was drawn in a floor plan view.
It came into dynamo as a rectangle (I looked from all angles).
The offset however gave two of the lines (the parallel shorter ends) a Z coordinate other than 0 while the other two (longer opposite sides) remained on the same Z coordinate as the original rectangle.
I re-drew my Revit rectangle using a property line and the offset now works.
I could definitely see lines drawn in a model view being placed on planes dependent on the direction theyâre drawn. This is pretty common for most elements. Combining them into a polycurve like was recommended is the best way to make sure theyâre all planar.
1 Like
This makes sense to me because property lines have to be drawn on the XY Plane so they will always have the same âorientationâ. Even though we think of detail lines as 2-dimensional they maintain 3D properties.
1 Like
If you look at the script I posted I did that. The original rectangle was fine. Itâs the offset.
Very odd!
Also bear in mind my original Revit rectangle was click click (using the rectangle tool, not 4 separate lines in a chain)⌠so how could the Z axis be different for two of the lines?
Oh, I didnât realise theyâd have any 3D properties at all.
Whatâs the logic behind that do you know?
Thanks for the replies btw guys even if itâs still a mystery 
As @AmolShah said, youâll need to flatten the list of curves before combining them into a polycurve. Right now youâre turning your 4 separate lines into 4 separate polycurves, which isnât really doing anything. You want 1 combined polycurve to offset.
Revit still has to draw 4 separate lines. The Z-coordinate values for the lines donât differ, but the planes they exist on do. Again, my guess is that itâs based on the direction the lines are drawn.
Everything has 3D properties even if some of those properties are locked out of one plane. Iâm guessing detail lines keeps some of these properties because they can be converted into model lines.
1 Like
What is the âhostâ of the item you clicked on to draw the line? Itâs VERY easy to associate content to a differing work plane. This is by design to make tools like the âpick lineâ work effectively without throwing many ânot on planeâ errors.
You will find a great many âoh I didnât realize Revit did THATâ moments as you get further and further into computational geometry within the Revit framework. Sadly as an application which does âeverythingâ pretty well it means the âodditiesâ are frequent rather than rare.
It was a blank canvas. The view was a level 0 floor plan.
I used a detail line and the rectangle tool.
I also tried it again using the line tool and drew a chain.
Both reproduced the same result. 
I mean tbh, I can use something else so itâs not an issue but I am interested in why .