PFL_INTERACT=TRUE selects interactive control of profiling tasks.
When interactive profiling is selected, a graphics cursor can be used to specify the required attributes of each pixel in the spatial profile. The characteristics may be globally applicable, or specified independently for each order. In addition, any polynomial profile-fitting is also performed interactively, with the degree of polynomials used adjustable and the fits and residuals at each sub-sample position viewable.
Martin Clayton