MographCandy’s Dan Conrad reminds us that it is indeed possible to render splines in C4D without converting them to polygonal objects.
You have probably been told you cannot render splines in Cinema 4D. You must add a Sweep, Lathe, or Extrude of some sort to create geometry. However, there is a way to render splines using the Sketch and Toon effect
Most 3D application will not render curves out at all, only rendering surfaces. This is one of the things that makes applications such as LightWave or 3Ds Max unique, in that within that system you can have 1 or 2 point polygons, making it simple to render out things like strings or cables directly from curves or edges.
Other 3D applications such as Cinema 4d, Autodesk Maya, etc, have no capacity for rendering straight-out curves. However, as Dan notes, it is possible by using a different rendering method.
You can easily render out curves by using the sketch and toon effect in C4d, similar to adding a PaintFX stroke to a curve in Maya. This will render out the curve without converting it to a polygonal object, and it will also provide the flexibility of changing the look of the rendered output by using different sketch and toon looks.
