seamless material mesh / landscape integration

hey guys !

i want to integrate a mesh to a landscape seamlessely .
for that i use vertex painting on the mesh to paint borders.
and a second painting layer on landscape that use same texture .

both of them use worldspace for the uv coordinate .
and it work fine ! so i have seamless texture between the mesh border and the landscape . BUT ! ^^

the lighting (or something like that) make the seam very very noticeable :slight_smile:
i am using a standard skylight and a moveable lightsource .

any idea on how to deal with that ?
if not any idea on how to make something like this is welcome .

ps : the mesh is actually a simple plane exported with blender and have one side material