The default terrain engine for osgEarth renders an unlimited number of image layers using a tile-level multipass blending technique.
<map> <options> <terrain driver = "mp" skirt_ratio = "0.05" color = "#ffffffff" normalize_edges = "false" incremental_update = "false" quick_release_gl_objects = "true" min_tile_range_factor = "7.0" cluster_culling = "true" />
skirt_ratio: The “skirt” is a piece of vertical geometry that hides gaps between adjacent tiles with different levels of detail. This property sets the ratio of skirt height to the width of the tile. color: Color of the underlying terrain (without imagery) in HTML format. Default = “#ffffffff” (opaque white). You can adjust the alpha to get transparency. normalize_edges: Post-process the normal vectors on tile boundaries to smooth them across tiles, making the tile boundaries less visible when not using imagery. incremental_update: When enabled, only visible tiles update when the map model changes (i.e., when layers are added or removed). Non-visible terrain tiles (like those at lower LODs) don’t update until they come into view. quick_release_gl_objects: When true, installs a module that releases GL resources immediately when a tile pages out. This can prevent memory run-up when traversing a paged terrain at high speed. Disabling quick-release may help achieve a more consistent frame rate.
min_tile_range_factor: The “maximum visible distance” ratio for all tiles. The maximum visible distance is computed as tile radius * this value. (default = 7.0) cluster_culling: Cluster culling discards back-facing tiles by default. You can disable it be setting this to
false, for example if you want to go underground and look up at the surface.