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Addingremoving uv curves to a surface mesh

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Symptom "I cannot locate the command for adding or removing UV curves to/from surface meshes."

Cause This feature is not yet available in the current version of SOFTIMAGE|XSI.

Solution

We can circumvent the current situation by using the Loft command to recreate the model - omitting or adding the curves of interest:

Select the surface mesh.
From the Main Command Area's Selection filter, select the U or V Isoline filter.
In Model toolbar's Create toolset, select Surface>Loft.
In whichever view offers the best vantage point for lofting your object, start adding isolines along the surface in a linear fashion as of, and ending on, the starting curve.
Once the last curve has been defined, right-click to finish the operation: the Loft Property Page will open automatically for editing.

Before	Picking Isolines
Missing image Beforeloft.jpg Image:beforeloft.jpg

Tweak the surface as desired: start by normalizing the continuity by setting the Start and End Surface to G0 (Position) or G1 (Tangent). You can opt to close the surface, edit the number of subdivisions and/or adjust each U or Vs position via their respective Surface Curve Adaptor tab.
When repositioning the curves, notice how the weighting differs, depending on whether the G0 or G1 continuity option was selected.

Additional Information

<P>You might experience some difficulty interactively positioning the Start or End Isolines at the exact top or bottom tip of the surface mesh (e.g. the top isoline will be positioned at something like 0.03, instead of 0.00).

If surface precision is of significant importance in your modeling project, you can do the following:

Select the original surface mesh and, from the Model toolbar's Create toolset, choose the Curve>Extract from Surface command.
The Extract Curve Property Page will open; check the U or V direction box and slide the Position bar to 1.0 or 0.0, depending on whether you are to extracting it's first or last curve.
Repeat steps 1 and 2 for the opposite extreme.
Apply the Loft operation, but this time using a slightly different method:

Select the surface mesh and turn off its Selectability parameter: hit the Alt + Enter key combo, to open the surface's master Property Page, access the Visibility tab, disable the Selectability parameter and exit the Property Page.
From the Main Command Area's Selection filter, select the U or V Isoline filter.
In Model toolbar's Create toolset, select Surface>Loft
From whichever view offers the best outlook for lofting your object, pick the first extracted curve at one extreme of the surface, then define the Isolines in order (i.e. first to last, don't skip over then return to previous) and then pick the second extracted curve at the other extreme of your surface. Lastly, right-click to end the operation.
If necessary, tweak the parameters in the Loft Property Page that will have opened up automatically.

Note	The Loft result will add more U or V curves to the new surface mesh. To reduce the number of curves, select the mesh and, from the Model toolbar's Modify toolset, choose the Surface>Clean command: augment the Tolerance value for the parameter in the Clean Surface Property Page.

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Lofting result

Clean Surface