We are interested in obtaining one scale from another scale. One way to get one scale from another scale is to rearrange the intervals. The interval between the 1st and the 2nd note may be made short and the interval between the 2nd and the 3rd note may be made long. For example from the scale of the 29th mela Sankarabharanam, if the scale of Kharaharapriya has to be obtained, then the interval between the notes R and S is shortened, the interval between N AND S is lengthened and so on.
If the major scale of the western music is taken into account, and if the whole lock stock and barrel of the scale is shifted from C to G, then F sharp is obtained. The process by which a scale can be obtained from another scale, is the process of modal shift of tonic. Here the mode is retained. In other words the sequence of the intervals is retained. It must be remembered, that the tonic or the aahara sadja alone is not shifted.
Take for example, the scale of Sankarabharanam. It is S R2 G2 M1 P D2 N2 S. In this scale, if the Aadhara sadja, is shifted to the position of rsabha and if the interval between the svaras are maintained, then a new scale is obtained. Here only the scale is taken into account and not the raga. This is due to the fact that in carnatic music, each raga has the shape of its own, due to the various type of gamakas employed.