If you have photoshop the easiest way is to: open the texture> use the pen tool and create a path that follows the archway shape> then under the file 'pulldown' menu, select export> 'paths to illustrator'> open your file in Carrara> insert 'spline object'> import from the file pull down menue (drive the selection to wherever you saved the photoshop exported path)> and , TaDa, you should have a spline shape that is perfect for your texture. Hope this makes sense. Mark