More and more studios around the world are using Subdivision modelling in the early concept phase. The interactivity and smooth continuity allows designers to rapidly iterate different concepts. The same data can be used by the engineers to study the feasibility and the modellers to prepare and mill full size clay models. The clay model gets refined further and the scan data is sent back to the modeling department.
Usually at this stage, the model gets refitted/rebuilt manually. Although the Subd Retopo tool allows rapid creation of subd models on scan data, the resulting subd does not conform to the scan. This is because the retopo tool snaps the vertices of the subd to the reference data, and not the limit surface.
The following workflow will automatically snap the subd surfaces to the scan data. It depends on using the dynamo/dynamo player.
Rhino to Alias
Rhino surface geometry is internally represented as B-rep objects. Rhino can export geometry in a wide variety of formats. In my experience the transfer of Rhino data to Alias is best done by using DWG format.
- Ensure that the modeling tolerance is set to the same as in Alias.
- In Rhino save as DWG format.
- Choose 2004 Natural format.
- Ensure that the output is set to Solids and Surfaces.
- Open the file in Alias.
Fit Scan
Fit Scan function enables rapid surface fitting to the reference data. The reference data can be either cross-section curves ( degree 1) or mesh data.
There are many plug-ins in Alias using OpenAlias. Many of the old plug-ins related to polygons have become obsolete. The following are some of the plug-ins and their brief description.
bestFitPlane
"bestFitPlane" is a tool to create a best-fit construction plane to a curve or a set of curves.
Usage: To create a best-fit plane, select the desired curves to fit, and click the bestFitPlane tool. The construction plane will be created.
Installed under the Curve Edit palette.
Explicit modeling is a technique in which the surfaces and curves are modified by modifying the CVs and hulls explicitly and without any history. The move CV tool in the control panel enables the movement of CVs and Hull in different ways .. XYZ mode where the movement is restricted to the XYZ axis, Slide mode where the movement is restricted along the hull directions, NUV mode where the movement is restricted to the Normal, U parameter and V parameter (in case of surfaces) and project mode in which the movement is restricted to the hull direction including that of any external geometry. The following figure shows a small example of explicit modeling to align a curve to another.
