Creates a surface by sweeping a profile curve along two path curves or rails.
How to use
1. Click the Birail icon or choose the Tools > Surfaces > Birail command.
2. The program console prompts Pick profile curve.
3. Pick the curve you want to be swept along the rails from any view. Once picked, the curve turns green.
4. The program console prompts Pick rail curve #1 near start.
5. Pick the primary path curve. Once picked, it turns green.
6. The program console prompts Pick rail curve #2 near start.
7. Pick the secondary path curve.
Important note: The point where you pick rail #2 determines how the birail surface will result. In order to avoid a twisted surface, rail curve #2 should be picked as illustrated in the pictures below.
Options
Profile curve
To change the profile curve.
Views / Modeling Tool panel. Switch the Replace check button on and pick another profile curve in the scene. The surface will automatically be modified.
Rail #1
To change the primary path curve.
Views / Modeling Tool panel. Switch the Replace check button on and pick another rail in the scene. The birail surface will automatically be modified.
Rail #2
To change the secondary path curve.
Views / Modeling Tool panel. Switch the Replace check button on and pick another rail in the scene. The birail surface will automatically be modified.
Point on rail #1
To define the point on the profile curve coincident with the rail #1.
Modeling Tool panel. The profile curve is parametrically defined in the interval [0..1], which means that 0 is the starting point and 1 is the ending point. Any other value between 0 and 1 defines a point somewhere in between the starting and the ending point. You can set the value either by moving the slider or by typing it in the data field and pressing Enter. The profile curve is oriented and scaled so that the defined point always lies on the rail #1.
Point on rail #2
To define the point on the profile curve coincident with the rail #2.
Modeling Tool panel. The profile curve is parametrically defined in the interval [0..1], which means that 0 is the starting point and 1 is the ending point. Any other value between 0 and 1 defines a point somewhere in between the starting and the ending point. You can set the value either by moving the slider or by typing it in the data field and pressing Enter. The profile curve is oriented and scaled so that the defined point always lies on the rail #2.
Accuracy
To control the number of points on the surface along the rails. This parameter does not affect the parametric surface but only the NURBS Surface that is created when you use the NURBS Surface Editing command or you collapse the Construction Tree.
Modeling Tool panel. Switch the chosen radio button on. You have the following options:
Point factor: the number of points is equal to the number of points of the rails multiplied by the number specified in the parameter Point factor.
Points number: the number of points is equal to the number specified in the parameter Points number.
Global 3D tol: the number of points is calculated so that the surface does not deviate from the rails more than the global 3D tolerance (see Surface modeling tolerance in the Units section of the program Preferences).
User 3D tol: the number of points is calculated so that the surface does not deviate from the rails more than the value specified in the parameter User 3D tol.
Options
To invert the rails normals.
Modeling Tool panel. Switch on the Invert rail #1 and/or Invert rail #2 check buttons.
See also:
Extrude to create a surface by extruding a cross sectional profile along a specified direction.
Loft to create a surface by sweeping two or more profile curves along a path.
Pipe to create a surface by sweeping a cross sectional profile curve along an extrusion path.