For the 3-D skeleton:
The techniques used for creating the dog skeletal bones were much the same as those for the outer skin. Some bones I started as NURBS and then converted to Polygons, e.g. the pelvis. Others I started as Polygons, e.g. the femur and tibia. I planned on having only polygons at the end so that I can use them in Motion Builder 5, the mocap cleaning and animating software. Now, since I am unable to get my animation skeleton to follow the marker data closely in Motion Builder, I will most likely do all my binding and rigging in Maya 5.
I scanned different views of dog bone illustrations from "Miller's Anatomy of the Dog." I used these as textures on polygon planes behind my bone models to serve as guides in the shaping process. View example.
Not all skeletal bones are completely done. For the sake of time, I'm going to have to cut back on the detailing of bone surfaces. I'd like to finish the sacrum, front legs, and vertebrae for my final presentation to the vet students. Below are links to images of the current skeleton.
I created a Nurbs sphere for half of the Pelvis, and worked on sculpting this, with a scan of a dog's pelvis on a polygon plane behind the 3-d pelvis. View half NURBS pelvis.
I duplicated it creating an instance that would inherit all the transforms I applied to the first side of the pelvis. View screen capture of instanced copy.
I created a curve on the surface for the Obturator Foramen. I thought it would trim all the way through the object leaving a hole, but it only cut a hole in the top of the pelvis, like a hole in a pop can.
I undid this and then tried lofting two of the same shaped curves together to form a cylinder, in hopes of performing a Boolean subtraction. When I tried to implement this, I got an error message about a Nurbs Shell. It didn’t work. View cylinder placement before boolean attempt. Note the circular curves on the surface of the pelvic bones for the trim that I tried above.
At this point I converted the Nurbs half pelvis to a polygon. Modify > Convert > Nurbs to Polygons. I deleted some faces on the inner side of the half pelvis where both halves would join up. View deleted faces example. I duplicated the half with an X scale set to –1. I made a copy instead of an instance. I displayed the surface normals to make sure they were all pointing outward. Then I combined the two Polygon halves.
Next, I merged the edges of the polygons together to form one whole pelvis. I converted the lofted nurbs curve cylinder to a polygon. I moved it into place over half of the pelvis. I then did Freeze Transformations on it to zero everything out. Then I duplicated it with an X scale of –1. I moved the duplicated cylinder onto the other half of the pelvis. I then did Boolean > Difference operations on both to get holes in the pelvis for the obturator foramen. View the polygon pelvis after boolean.
View the movie of the lumbar vertebra. This was another complex form to create. I didn't take screen captures of every step, but will explain how I made it.
I first created a polygon cylinder for the body of the vertebra. I got its shape to match the illustration of the lumbar vertebra. Again, I was using scanned orthographic views of a lumbar vertebra as guides and worked in x-ray view. View orthographic illustrations.
I borrowed the top tail bone to start the shape for the spinous process on the back of the vertebra. I selected vertices and scaled and moved them until I was happy with the shape.
I then duplicated the spinous process to form the tranverse processes on the sides of the vertebra. I scaled and moved vertices until I was happy with the shape.
To form the the cranial and caudal processes that project upward and downward off the back of the vertebra, I kept splitting polygons to create knew faces to extrude. I extruded faces to form the bridge between the processes and the body of the vertebra. Then I extruded more faces to get the upward and downward projections. I first had some very blockish square forms. I scaled and moved vertices until happy with the shape. View the primitive vertebra.
I next joined the spinous process to the cranial/caudal processes. I added edges with the split polygon tool. I extruded a couple faces. I had to match edges on all objects so that I could join them. I deleted the interior faces, combined the objects, then used the merge edge tool to join them (very much like I joined the legs to the torso of the outer skin dog models).
I did the same process for joining the transverse processes to the cranial and caudal processes.
At some point, I smoothed the normals of the vertebra to make it look less angular. This can be done by going under Edit Polygons > Normals > Soften/Harden > and clicking on "All Soft."
What happens when you accidently extrude a surface when modeling
Sometimes, no matter how careful you try to be when modeling, you accidently hit a button or command you didn't intend. I accidently selected the extrude button when modeling the first claw. This duplicated my surface, or made them sort of two sided. I first noticed it when I was adjusting some of the edges in x-ray mode. View example. I checked the normals and there were normals pointing inward on the inner surfaces and outward on the outer surface. The way I fixed this, was to go inside the 3-d model and select rings of faces and delete them one by one. I did this until I had only one set of surfaces left. The problem this created was with polygons no longer being connected. View example. I then had to go through ever single vertex on this object and move it around to see if it belonged to a continuous surface. If not, I had to do Edit Polygons > Merge Vertices to sew them back together. Very time consuming and painful.
Another naive mistake
When I first created my femur, I combined polygon shapes without matching up edges for merging later. So, I got many messy polygons protruding inside the object, instead of it being one continuously smooth surface. View example of head of femur. I didn't want to remodel this, so I went inside the 3-d model again, and removed every surface sticking inward. I had to add edges by splitting polygons, and merge vertices. It was also time consuming. View the x-ray of the corrected femoral head.
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