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# True 3D Polylines; Feature Lines that correctly creates 3D Curves

## True 3D Polylines; Feature Lines that correctly creates 3D Curves

I would like to see True 3D Polylines; Feature Lines that correctly creates 3D Curves, especially from Survey Cogo Points.  For example 3 Cogo points will create both a horizontal and a vertical curve.

Mentor

@nmessina, I am not sure what you are asking for. Actual 3d polylines do not have curved segments. You can convert a 2D polyline with a curve to a 3D polyline or explode a feature line with curves into a 3D polyline. The resulting 3D polyline have tessellated representations of the curves.

When I draw a feature line through three points, then fit a curve from start point to end point, the resulting curved feature line follows a circular arc when viewed In plan view. The curve has a snapable center and measurable radius and delta. That is smarter that a 3D polyline.

I guess that the question is what do you want for the side or elevation view? Currently the feature line segments are straight graded between the three points. This results in 2 lines, if viewed from the side. Would you want a circular arc or a parabola fit between these points?

Collaborator

Chris,

Just as 3 points can define a "horizontal curve" they can also define a "vertical curve".   Currently the when creating a 3DPOLY there is no option for curves.  Think of it this way, in Civil 3D you can define a horizontal alignment and vertical alignment, this is essentially what I am looking for our of 3DPOLY and feature lines.

At least, I would like to see a curve option in the 3DPOLY that will creates a curve and automatically adds a vertex in the curve at the 2nd point location with the elevation of that second point.  While this would not create a "vertical curve" it would at least create two curves, of the same radius, so that you can have a vertical grade change along the curve.

Mentor

@nmessina, I see what you are talking about now.

Assuming that you want a circular arc in plan view, this would imply that the "line" falls on a cylinder that is perpendicular to the X-Y plane. The line segment from the first point to the second point would be a segment of an ellipse. The line segment from the second point to the third point would be a segment of an different ellipse.

What you ask for can be done. The Feature lines already carry horizontal curve data, and could be improved to carry segment by segment vertical curve data. Since feature lines are part of Civil 3d, the Civil 3D Team could implement this.

3D polylines are a part of base AutoCAD. The AutoCAD team controls them. The 3D polyline is used throughout the Autodesk product line so I do not think it is likely that the AutoCAD team will enhance this. It did happen (halfway) with Linetypes so there is hope.

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