Cable-Driven Parallel Robots (CDPRs) are a type of parallel robots that have the particularity of using cables as legs. CDPRs have several advantages such as large workspaces, high acceleration and high payload capacity. However, CDPRs present also some drawbacks such as the possible collisions between their cables and environment. Therefore, this paper is about the geometric determination of the cable-cylinder interference regions in the workspace of a CDPR. The cables are considered massless and straight. Then, the boundaries of the interference regions onto the cylinder form a closed loop composed of arcs and straight line segments that can be expressed symbolically. Those geometric entities generate truncated cones and planes corresponding to the boundaries of the volume of interferences. Finally, a methodology is described to trace the cable-cylinder interference free constant orientation workspace of CDPRs.