| Rail Sweep Tangency Controls Quick Help |
|  | Quick Help Home nPower Software Home |
| Overview |
| The Pwr_RailSweep command sweeps one or more shape curves along a set of one or more rail curves with optional tangency constraints. This submenu sets up the tangency controls for the Power Rail Sweep. The tangency controls allow you to control the shape of your rail sweep surface by controling how your profile is modified by the tangency controls along the rails. For further information on using the Power Rail Sweep command, see the Power Rail Sweep documentation. |
| Rail Options |
| Modify only Selected: Turn this option on if you want to change the tangency control settings on specific rails. Without this option turned on, your modifications will apply to all of the rails in your rail sweep. Use Given Rails: Use the selected rails in the surface construction to exactly interpolate the rail curves. Reapproximate Rails: Re-approximate rails using least squared fitting algorithm to reduce the number of knots. This should be used when there are too many knots in the original rails but some degree of interpolation is required. Don't Use Rails: Ignore the rails when the surface is constructed. It will only approximate the rails. |
| Rail Tangency Options |
| The rail tangency options controls how the profile is modified in response to tangent fields along rails. If you utilize these options with sweep with minimal number of interior control points the result is equivalent to a blend. Additional control points may be added to achieve the desired continuity along the rails. No Tangency: Ignore any Rail tangency information just utilize standard sweeping techniques. To Tangent Plane: Drop one or more of the interior control points down to the tangent field surface. To Tangent Vector: Drop the control point down as above but also align the vector defined between the first and next (or last and previous) control points with the orientation of the tangent field surface. To G1 Continuity: The same as "To Tangent Vector" but also utilize the magnitude of the tangent field surface. To Tangent / Curvature: Same as "To Tangent Vector" but also modify additional interior control points to achieve geometric curvature continuity. To G2 Continuity: Same as "G1 Continuity" with additional geometric curvature continuity. To G3 Continuity: Same as "G2 Continuity" with third derivative continuity (speed of change of the curvature). |
| Rail Control Options |
| Tangent Strength: This option controls scales all of the tangent fields which have G1, G2 or G3 continuity. It has no effect on the other cases with don't utilize magnitude of the tangent field surface. Points To Modify: This controls how many points in from the end to modify if rail tangency is applied. Typically it is 1 for tangent, 2 for curvature and 3 for G3 continuity. You may specify more points to modify the interior of the curve. If you have a single rail sweep and want the entire curve to rotate with the tangent field around the rail, set this to a number greater than the number of control points in the shapes. Fall Off: If there are more than 1 points to modify the fall off will decrease the modification proportionally going away from ends of the shapes. Flip Tangent: Flip the tangent of the rail. Use Rotation of Rail: As the rail curves in space this option enables the shape to rotate with it as it moves along. If you turn this off, the orientation of the interior generated shapes will remain the same as the original shapes. Rail Sweep of an 8 Point Curve between two Rails which are surface edges Rail Sweep with "Tangent To Plane" tangency control set for the top Rail. Note how the second point has been projected up to the plane of the tangent field. Rail Sweep same as above except that we now modify 2 points. Note how the third point has moved up proportionally. Rail Sweep with "To G1 Continuity" set for the first rail. Note how it uses both the direction and magnitude of the tangent field if the Tangent Strength is set to 1.0 Same as above but with tangent strength set to 0.5 "To G2 Continuity" is set along the first rail with 1 point to be modified. Note that increase in number of control points. "To G2 Continuity" with 5 points being modified and no falloff. "To G2 Continuity" with 5 points being modified with "Fall Off" checked. Note how the points gradually moved. Flip Tangent: Flip the tangent of the rail. |