TITLE: Tynwald Cross NAME: Steve Strickland COUNTRY: USA EMAIL: steve@puzzlecraft.com WEBPAGE: http://www.puzzlecraft.com TOPIC: Landmarks COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT. JPGFILE: tynwald.jpg ZIPFILE: tynwald.zip RENDERER USED: Pov-Unofficial 3.1 TOOLS USED: SplineR.inc and TomTree.inc RENDER TIME: 7 hours 6 minutes HARDWARE USED: PowerCenter Pro 210 IMAGE DESCRIPTION: The Tynwald War Memorial Cross was designed by P. M. C. Kermode. It is a 30 ft high, ringed cross (ie the arms are joined by a circle) in stone that stands between St. Johns Church and Tynwald Hill on the Isle of Mann. It is an outstanding example of a Celtic Cross. The main feature of Celtic Crosses is the knotwork and braiding. The Tynwald Cross is very difficult to photograph because it is a large monument with a lot of fine detail. I have been unable to locate a photograph that captures both the large and small scales. I therefore decided that a 3D rendering might accomplish this. DESCRIPTION OF HOW THIS IMAGE WAS CREATED: The key to doing a project like this is organization. I first sketched the geometry out in Adobe Illustrator and laid out a coordinate grid. I then used the coordinates in my POV scripts to build the cross and all of the knots and braiding. The main pieces were constructed with primitive objects and some CSG. I was unable to use the conic_sweep on the tapered sections because I was not able to exactly specify the corner points (the manual is vague here). I decided to use a patch object instead so that every point could be precisely located. I could also have built a polygon using location and angle information from the Illustrator master file. The knotwork was started as a sphere_sweep, but I found that the Catmull-Rom spline was unuseable because of lack of a high quality spline editor. I decided to employ the bezier_spline so that I could use Adobe Illustrator for the design. Since POV-Ray cannot sphere_sweep a bezier I then tested a number of macros, finally settling on Chris Colefax's SplineR macro. I drew the knotwork in Illustrator using Celtic Knot techniques found on the web (search for "celtic knot"). I then picked off the coordinates from the Illustrator file and wrote them into the Spline scripts, adding the z axis data for depth. I used the SplineR macro to "stroke" the splines with spheres. Some careful conversions were required for this. The Illustrator coordinates for the control handles are in global coordinates and the SplineR coordinates use a local grid. Also, the directions of the control points must be reversed on all 3 axes. I quickly learned that this technique used up massive quantities of my computer's resources. I was forced to reduce the overhead after the very first knot. I thought this project might be impossible on my machine. First, I broke most of the splines into single segments and gave each segment the minimum number of spheres. Next, I replaced the straight segments with cylinders. Finally, I eliminated duplicate spline segments and replaced them with copies that were rotated and translated. Instead of 1 large spline to render a knot, I now had 17 splines plus 3 cylinders. This vastly reduced the parsing overhead, by a factor of 25 or more. This resulted in a large number of splines, but each one was marked on the master Illustrator file. If a spline was wrong, I could locate the script for it very quickly. Furthermore, by using the master Illustrator coordinates I was able to quickly position all the pieces together. However, mixing splines and cylinders has it's drawbacks - the final object gets tricky to revise, especially if the spheres have been flattened. Finally, I used the TomTree macro to add a little landscaping.