Surface Patching

This option creates a new object by warping a flat patch to pass through a number of selected points. These points can be defined in two ways. Any active part of the surface (coloured in yellow) will be used and it is possible to also use landmarks placed (please note that all of these markers will be used). There is one control parameter, tension, which modifies the fitting process. The default value is 0.5, higher tension (maximum is 0.9) will cause the surface to be more tightly streched, flattening surfaces between control points and sharpening the local curvature at the control points. Lower tension (minimum 0.1) may result in a smoother surface which does not fit exactly to the control points.

It is important that the edit options are used to define an active region before attempting to create a patch. If the whole object is selected, it is very unlikely that a good patch will be achieved. The most reliable editing method is to apply "select none" (which paints the whole surface orange) and then just paint the wanted regions (in yellow). Any number of patches can be painted but the warped patch cannot bend more than 180 degrees so it cannot patch a surface that bends more than 90 degrees from the mean direction. This starting orientation of the plane is determined by fitting the best (least square error) plane to all of the patches and landmarks. In the case of a localised defect in a surface (see fig1) then a band of good surface around the defect should suffice to create a good patch. If the band is too narrow, it will inadequately define the local surface orientation. Conversely, the larger the area selected (in yellow) the longer it will take to calculate the patch.

The resulting patch may need to be trimmed in order to keep only the region of interest. This can be achieved with the edit options.

The difference of surfaces menu can be used to measure the change between the original and patched surfaces.

The Intersect Surfaces function in the options menu can be used to create a new object which fits in the defect.

Back to index