i have such a problem that i need to interpolate bathymetry for a strait, with grid cells of about 50 or 100m. In the data i have depths from 0.2 - 8m. Now my problem is that using any interpolation method (IDW, kriging, natural neighbour) i get values starting from the depth of 2m, although the most of the strait is relatively shallower than 2m. I also tried to interpolate as a spline, but that didn't also work out. Is there a way i could define the lower limit to my interpolation or what can i do to solve this problem?