PART 2: MODELING THE ARTERIES
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The main point I want to make in this tutorial is to explain how to make arteries that follow the surface of the heart. One of the main uses I have for this model is to create diagrams of coronary heart disease, which involves the blockage of the arteries that nourish the muscles of the heart. Therefore I wanted good quality arteries made of geometry. A bump map would not be good enough for the close up views I want.

STEP 1
To create the coronary arteries I first began in Adobe Illustrator. I assembled screen shots of the model form five directions. On top of the screen shots I drew the arteries.

STEP 2
After I was satisfied with the shape of the arteries I used Illustrator’s outline stroke command to create closed polygons.

STEP 3
I imported the illustrator shapes into Modeler using the EPSF loader plugin. I extruded the shapes to be deep enough to intersect the surface of the heart. I positioned the shapes so that they intersected the heart of the front sides, back and bottom.

STEP 4
I made a copy of the heart in a new layer. I used the freeze command to create a shape suitable for boolean operations. I used the Boolean-intersect command to cut the artery lines out of the heart shape. I then used the merge points command with a fixed radius to reduce the number of points to a comfortable number.

STEP 5
I selected the points along each branch of the arteries and used the Make Open Spline command to created spline curves. The result is that I have splines that exactly follow the contour of the surface of the heart.

STEP 6
I selected a single point at the end of each spline and copied them to a new layer. I used the Point-Clone-Plus command to copy a group of 3 quads to the endpoint of each spline.

I then selected each group of polygons individually and rotated them so that the normal pointed in the direction of the spline.



Then, in a tedious and time-consuming process, I copied each spline to a new layer. Next I hid all the quads except one group. I set the layer with the corresponding spline to be the background layer.



Then I used the Rail Extrude command to extrude the polygons along the spline. I repeated this process for each spline individually.

STEP 7
The three different sizes of quads were to help in the tapering of the veins. To further taper the ends of the tubes I selected each 4 point intersection and used the scale tool with the action mode set to scale from the selection center.

I joined the tubes together with quads. The plugin PolySew (available from http://www.m2estudios.com/plugins.html) was very helpful for this step. Thank you m2e Studios for creating this useful plugin.

The arteries textured and converted to subpatch mode.

The result of all that work is arteries that exactly follow the contour of the heart's surface.