scribing is different than "constructing"
If you have an existing wall or curve you can accurately "duplicate" the surface using a scribe. You can not duplicate the curve by "constructing" it with straight edges and a compass ... easily or accurately without a lot of measurements and some trail and error.
In the automotive design world, we had to duplicate the entire surface of a car to flip the design to the opposite side for comparison. We had highly skilled wood workers who spent years doing this and it was extremely accurate. We also did some of this work ourselves when required. A section of the car was marked off and covered with masking tape which was then colored with crayon. As the template got very close to "perfect" the crayola would rub off evenly across the thin plywood and that was an indicator of accuracy. It has to be as close as possible to match other sections done in the same manner. You couldn't use a compass to construct these curves.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)