In order to fit in memory large area and retain details in area of interest - all this without swapping in and out tiles not visible - test a quadtree subdivision of the selected area, and compute boundary values based on that.
Using tiles sized 260x260 might allow to store border values also against lower ZL tiles (the higher ZL tiles would be the one that has to "adapt" against the lower one)
Alternately store (all) borders in mip level 1, so that the original texture is intact (might be useful for tess shaders)
In order to fit in memory large area and retain details in area of interest - all this without swapping in and out tiles not visible - test a quadtree subdivision of the selected area, and compute boundary values based on that.
Using tiles sized 260x260 might allow to store border values also against lower ZL tiles (the higher ZL tiles would be the one that has to "adapt" against the lower one) Alternately store (all) borders in mip level 1, so that the original texture is intact (might be useful for tess shaders)