Smoothing Methods

Once we have a reasonable initial hull form derived from tangency constraints and the use of a smoothing method we can consider using the underlining data of the patches. To do this, switch off all tangency constraints (deselect Use tange targets) select smoothing (None) and under the Data Points page select Use data points (see Patch Options Dialog for further information). Again it must be stressed that we are assuming that the underlying Lines curves are of good quality if we are using this particular approach. It is as if the patches including data are to be stretched over the entire set of curves.

Figure 3:148. The entire set of curves over which the data patches will be fitted.

Figure 3:149. Surface generated from tangency constraints and a smoothing method

Figure 3:150. Surface fitted to data without smoothing

It is important at this stage to note that some patches may not have sufficient data to define their interior. In particular long thin ribbon like patches that have only a few curves crossing them. A stem bar is typical of this type of patch. These patches are often best defined only by boundary information. This is achieved by selecting the options for that individual patch selecting Sculpted as the smoothing method and deselecting the Use data points tick box.

Figure 3:151. Patch with insufficient data to hold shape

Figure 3:152. Patch generated with sculptured smoothing and no data

It may be the case that all but one or two patches are relatively smooth. This does not include those that can be corrected by a small amount of manual fairing (we will deal with this topic below). For patches that are unfair due to the fact the underlying data is slightly unfair it may be necessary to combine data with one of the fairing methods. It is worth experimenting with the various methods to see which gives the best result. Also try fitting with and without tangency constraints. If this fails it may be worth trying the same options but without data. Again, try with and without tangency.

In the figure below we see a patch which is created using data, it can be seen that it is not fair. The subsequent figure shows the effects of incorporating the Sculpted method with data. This improves the fairness considerably. The next figure shows the effect of a small amount of manual fairing.

Figure 3:153. Patch fitted with data only

Figure 3:154. Patch fitted with smoothing and data

Figure 3:155. Patch after some manual fairing

We may wish to enforce tangency conditions for a single patch. In general tangency is controlled at two levels. Firstly globally when generating all patches, tangency constraints are either on or off for all patches. Secondly this can then be altered for an individual patch by toggling the tangent controls on or off.

Figure 3:156. Tangent controls

Once the desired tangency condition has been selected, then the patch must be regenerated individually for these conditions to take effect. This is done by making a right mouse click over the patch and filling in the appropriate parts of the Patch Options dialog. It is important that the Use tange target on the Tangency page is ticked, if not the tangency controls will be ignored and no tangency is set.

Some patches are curved in one direction only. Sometimes these type of patches are best fitted without data and using one of the energy methods. A useful feature of the energy methods is that using them to fit a patch enables the patch to be stretched taut in one particular direction, producing something resembling a swept patch. This is achieved within the Patch Options dialog on the Smoothing page. First select one of the two energy smoothing methods, deselect the Automatic smoothing function parameter, then set either the A or the C parameter to 0 while keeping all others as 1 (see Smoothing Page and Building the Surface - Smoothing Page of the Patch Options Dialog).

Figure 3:157. Patches fitted with sculpted smoothing

Figure 3:158. Top two patches fitted with energy smoothing, and with user defined parameters

If all these approaches fail then it will be necessary to either manually fair the patch or return to the lines definition and fair the underlying curves.