We present a patch-based terrain synthesis framework constrained by user-specified curvilinear features such as ridges and valleys. The framework copies patches of a Digital Elevation model from a real landscape onto the output terrain such that the output contains the curvilinear features specified by the user and exhibit the characteristics of the real landscape. A user specifies where terrain features appear in the generated terrain by providing a 2D sketch map or drawing 2.5D sketched curves in the sketching interface. Features are automatically extracted from the user constraints and a real landscape, and a patch-based texture synthesis guided by these features produces a realistic terrain that fits the user constraints. A novel patch merging technique is proposed to remove boundary artifacts created by overlapping patches.
We show that terrains generated by our system are more realistic than current state-of-the-art terrain synthesis methods. We also present two GPU acceleration techniques and show that these parallel implementations accelerate the matching process by 6 times compared to the optimized CPU version.