Computer method and system draws a 3D object, by sketching at least one first stroke (ST1) in a first plane (PL1) rendered in a first viewing frustum corresponding to a first pose of a virtual camera. The first plane (PL1) is orthogonal to a second (PL2) and a third plane (PL3). In response to a command of a user switching from the first pose to a second pose of the virtual camera, the method and system switches from the first viewing frustum to a second viewing frustum corresponding to the second pose of the virtual camera. The second viewing frustum is bounded by a near plane on the side of the virtual camera. Next a plane is selected as current drawing plane. The selected plane is among the first (PL1), the second (PL2) and the third plane (PL3), whose normal is the closest to the normal of the near plane. At least one second stroke (ST2) is then sketched in the current drawing plane.