Trimmed Surfaces Maya 2013

Transcription

1 Michael O'Rourke Trimmed Surfaces Maya 2013 Concepts Trimming works only on patches (in Maya, this means NURBS patches) Does not work with polygonal models A trim can look similar to a Boolean difference operation, because it appears to cut away a portion of the surface A trim is very different than a Boolean: A trim does not really create a hole in the surface It merely makes a region (or several regions) of the surface invisible A trim does not calculate the interior surface of a hole Two-Step Operation To trim a NURBS surface requires two steps: Step 1 = Create a trim curve on the surface of your object This curve indicates where the trim will be Step 2 = Trim the surface based on the shape of that curve Step 1 Create a curve on the surface Go to the Surfaces module First, >Create > NURBS Primitives > Sphere Make sure it is NURBS, not polgyon Three approaches to creating the trim curve: Method 1 for creating a trim curve = Project a curve onto the surface

2 In one of the orthographic windows, >Create >CV Curve Tool or >EP Curve Tool, to draw a curve Move or rotate the curve so it can project from that window onto the sphere It doesn t matter how far the curve is from the sphere, as long as it will project onto it Click in the orthographic window to select that window Select the sphere Shift-select the curve >Edit NURBS >Project Curve on Surface [] >Edit >Reset Settings this will use the active window for the projection >Project The curve is projected onto the sphere You should see the trim curve on the surface of the sphere To improve display, in Persp window >Shading >Smooth Shade All >Shading >X-ray Click select your original curve It becomes green The projected curve becomes purple Construction history is active, so Translate your original curve a bit

3 As you move it, the trim curve on the sphere is recalculated, and moves Select both your sphere and the curve and move them off to the side Method 2 for creating a trim curve = Intersect two surfaces Create two NURBS spheres Translate them so they interpenetrate Select the first sphere; shift-select the second >Edit NURBS >Intersect Surfaces A trim curve is produce where they intersect Try moving or scaling one of the spheres The trim curve is recalculated in real-time Select both of your spheres and move them off to the side Method 3 for creating a trim curve = Draw a curve directly on a live surface A live surface forces your curves to snap to the surface This technique works best for relatively flat surfaces It is very difficult to control for a closed surface, like a sphere, because your live curve may be mistakenly drawn on the back side

4 >Create > NURBS Primitives >Plane Translate some of its CVs to give it some curvature Select the surface >Modify >Make Live This forces your curve-drawing to snap to that surface The surface changes color to indicate this >Create >CV Curve Tool or >EP Curve Tool Then draw directly on the surface of the curve Select the curve Translate it It always stays on the surface following the curvature of the surface When you are finished drawing, >Modify >Make Not Live, to turn off live mode Step 2 Trim the surface Once you have a trim curve on the surface, (using any one of the above three methods) you can now (finally!) trim the surface Begin with the NURBS plane you just were working on Select the NURBS plane >Edit Nurbs >Trim Tool The cursor changes to an arrow Click the cursor inside that region of the surface you want to keep You can click on the marker and drag it around to other regions

5 Hit the Enter key Maya trims the surface Leaving a hole within the surface >Window >Hypergraph Notice that trimming did not create a new surface (unlike Boolean operations, which do) It only hides the trimmed portion of the surface Try trimming your other tests: Select the object to be trimmed (It already has a trim curve on it) >Edit Nurbs >Trim Tool Select the area to be retained Hit Enter Construction History As long as construction history remains active, you can change the trimmed surface by moving the curve-on-surface that created it For example, move the original curve that was projected Or move the object that was intersected You can even animate the trim, by keyframing the position of the curve or object that created the trim curve If you delete the construction history, moving the objects no longer changes the trim

6 Untrimming Even if construction history has been deleted, you can still untrim a trimmed surface You can do this because the trim operation does not actually delete any geometry; it only makes certain regions invisible Select the trimmed surface >Edit Nurbs >Untrim Surfaces