public void ToTerrainRegion( out Region reg )
{
Region offset = TerrainManager.use.currentTerrainRegion;
reg.left = Mathf.Max(0, left-offset.left);
reg.right = Mathf.Min((int)TerrainManager.terrainData.size.x-1, right-offset.left);
reg.top = Mathf.Min((int)TerrainManager.terrainData.size.z-1, top-offset.bottom);
reg.bottom = Mathf.Max(0, bottom-offset.bottom);
}