Stitching a NURBS character
Arms to Body

As a Maya Teacher's Assistant, one of the most asked questions is the process of stitching a NURBS character's arms to the body. Here, I will attempt to illustrate the process that has been the most successful with me. The way I do it causes a few more pieces than some people would want, so feel free to try variants that do not cut the body up so much.

My scene is from my Super Hero character as seen in my 3D Stills gallery. In Figure 1, you can see that the body and arm have both been fully shaped. Also, the body is cut in half. This will simplify the process by allowing me to simply mirror the right side after a successful stitch.Figure 1
In Figure 2, select two horizontal isoparms on the body that will allow the arm enough room to merge nicely. If the area you block off is smaller than the arm, unseemly wrinkles will muck up the geometry. After selecting your desired horizontal isoparms, detach them (Edit NURBS > Detach Surface).Figure 2
In Figure 3, after detaching horizontally, select 2 vertical isoparms from the detached section that will allow the arm enough room to merge nicely. Detach the surface. Then, delete the square portion your cuts have made to display the hole for the arm to merge into (Figure 4).Figure 3Figure 4
This is where you may wish to do your model differently. I usually proceed to cut the body a few more times. The reason being, that it ensures your changes wll have a smooth transition, and in my opinion allows for better results. In any case, as seen in Figure 5, I cut the body horizontally 2 more times, one isoparm above and below my original cuts.Figure 5
I then cut these new strips vertically along the same isoparms I cut vertically before (Figure 6).Figure 6
Next, detach the arm at the 4 corners that will meet up with the 4 corners of the arm socket hole (Figure 7).Figure 7
Once all these cuts have been made, select all the pieces and Delete their History (Edit > Delete by Type > History) and rebuild their surfaces (Edit NURBS > Rebuild Surface). In the Rebuild Surface Options, make sure 0 to #Spans, U and V, and CVs are all selected (Figure 8). This will ensure the surfaces keep their current number of spans. If for some reason, any of them do seem to have more than they should, rebuild those pieces to the number of spans they should have.Delete HistoryFigure 8
Now, check and make sure the pieces that are adjacent to each other have the same number of spans in the V direction. As you can see on my model (Figure 9), the spans do not match. Rebuild the arm piece to match the body piece (Figure 10). Do this for the rest of the pieces.Figure 9Figure 10
In some cases, you may see a situation like in Figure 11. If you look at the model and then at the spans, you can see that the spans seem to be opposite what the Attribute Editor states. To fix this, select the surface and open the Reverse Surface Direction Option Box (Edit NURBS > Reverse Surface Direction > Options). Select "Swap" and Apply (Figure 12). As you can see in Figure 13, the model itself doesn't change, but the spans are reversed.Figure 11Figure 12Figure 13
After fixing the spans on all pieces, Delete History and Rebuild all surfaces using 0 to #Spans, U and V, and CVs. Now, it's time for the Fillet. I like to use the Fillet Blend Tool (Edit NURBS > Fillet > Fillet Blend Tool). For it to work, you select the tool, then select an isoparm and press ENTER. Then select the next isoparm and press ENTER. The fillet is made between the two isoparms. As you can see in Figure 14, the fillet may twist. This is easily fixed. Select the body piece the fillet is attached to, and again go open the Reverse Surface Direction Options. This time, reverse the surface on either the U or V direction. If one doesn't work, undo (Z) and try the other (Figure 15). This twisting normally occurs twice. Once you've got all 4 fillets (Figure 16), Select all, Delete History, and Rebuild Surfaces.Figure 14Figure 15Figure 16
Now, Attach the Fillets to its corresponding Arm piece with Blend checked in the Attach Surface Options (Figure 17, Edit NURBS > Attach Surfaces > Options). Do this for all 4 arm sections (Figure 18). Once done, select all, Delete History, and Rebuild Surfaces.Figure 17Figure 18
At this point, we'll now attach the 4 arm sections together. When you do, you'll notice the corners come away from the body, leaving gaps. This is OK. The upcoming step for Global Stitch will fix this (Figure 19).Figure 19
In order to attach the last corner, you'll have to use Open/Close Surface with "Blend" turned on (Figure 20, Edit NURBS > Open/Close Surface > Options). When done, Delete all history, and Rebuild Surfaces.Figure 20
Now, it's time for the Global Stitch. Select all the surfaces, and open the Global Stitch Options (Figure 21, Edit NURBS > Stitch > Global Stitch > Options). In the Global Stitch options, turn on "Closest Knot", "Equal Params", and "Tangents." Apply.Figure 21
Press Ctrl+A to open the Attribute Editor for the Global Stitch. Scroll down to the bottom and turn Resistance all the way up to 1.0. Now, slowly edge the Max Seperation up. Keep a close watch on your model. When the 4 corners close together, stop moving the slider (Figure 22). If none of the settings on Max Seperation seem to work, try checking Stitch Partial Edges and try again. With the Global Stitch still on, you are now free to tweak your model to get rid of any unsightly wrinkles or other problems. The stitch will keep the many pieces together.Figure 22
Once your done, you have a stitched arm you can easily mirror for the other side! (Figure 23).Figure 23
I hope this tutorial has helped you! If any errors, questions, or suggestions, please contact me!

Michael McKinley