Abstract: A three-dimensional (3D) map display system displays a 3D map on which a ground surface and a feature are represented three-dimensionally. The 3D map display system includes (a) a map database for storing map data representing a 3D shape of the ground surface and the feature, (b) a first drawing unit for drawing the ground surface and the feature by executing depth determination by referring to the map database, and (c) a second drawing unit for drawing a target feature, which is a feature in which at least a part thereof is hidden by a ground surface or other features in the drawing by the first drawing unit, by overwriting the target feature on a drawing result by the first drawing unit by using the map data without executing depth determination with respect to the drawing result by the first drawing unit.

Abstract: A map database stores three-dimensional polygons of features, as well as water system polygons such as sea and lake and ground surface polygons. The map database stores map data in multiple levels having different levels of details, such as levels LVa to LVc. A procedure of displaying a three-dimensional map offsets the water systems relative to the ground surfaces, draws a map of a distant view area distant away from the viewpoint using map data at a low level of details, subsequently clears a depth buffer and newly draws a map of a close view area close to the viewpoint using map data at a high level of details. The offset is set to increase in the distant view area and decrease in the close view area. Increasing the offset in the distant view area avoids the occurrence of Z-fighting in the distant area from the viewpoint.

Abstract: A three-dimensional map is displayed in a bird's eye view with a stereoscopic effect of feature polygons by providing shading in an appropriate direction according to the gaze direction in a simulative manner. Shading wall polygons are set in addition to feature polygons in three-dimensional map data. The shading wall polygon is a virtual plate-like polygon provided vertically, for example, along a boundary of a feature polygon. When provided around the water system, the shading wall polygon is specified to be opaque on one surface viewed from the water system side and to be transparent on the opposite surface. The shading wall polygons are drawn along with the feature polygons in the process of displaying a map. The shading wall polygon is drawn in black, gray or the like only at a location where the surface specified to be opaque faces a gaze direction.

Abstract: In displaying a 3D map, a feature image is generated by perspective projection of the feature based on a predetermined position of the point of sight and a predetermined direction of the line of sight. A plate polygon on which characters are pasted is arranged in a virtual 3D space in a direction along a road and tilted from the ground surface, and parallel projection is applied to the plate polygon so as to generate a character image. A tilt angle between the plate polygon and the ground surface is set based on a display direction of the road and a display position of the character. Thus, by generating the feature image by perspective projection while generating the character image by parallel projection, negative effects such as crushing of distant characters can be avoided, whereby the characters can be displayed in three-dimensional shape without reducing visibility thereof.

Abstract: Representation of undulation with a light processing load is realized using three-dimensional ground surface data. Ground surface data representing a three-dimensional shape of a ground surface is stored in a map database. A two-dimensional image representing contrast of the ground surface is also generated by projecting the ground surface data by applying lighting thereto, and the two-dimensional image is stored in map data as a ground surface texture. In displaying the map, the ground surface texture is pasted on the ground surface data and perspective projection is performed. By such a configuration, even without applying lighting, a map can be provided which can give undulation of a ground surface with a light processing load.

Abstract: A 3D map representing a feature that cannot be visually recognized such as an underground structure is displayed without a sense of discomfort. Among features stored in the map database, underground structures such as tunnels are classified into transmissive objects, and other features into non-transmissive objects. Then, the transmissive objects and the non-transmissive objects are projected individually so as to generate a transmissive object projection view and a non-transmissive object projection view. The transmissive object projection view thus obtained is superposed on the non-transmissive object projection view with adjusted transmittance. Making the transmissive objects to be transmissive and superposing them enables to realize a map that appears to the user as if a ground surface or features which blocked the transmissive objects are made to be transmissive whereby the transmissive objects become visible.

Abstract: A thee-dimensional (3D) map display system displays a 3D map on which a ground surface and a feature are represented three-dimensionally. The 3D map display system includes (a) a map database for storing map data representing a 3D shape of the ground surface and the feature, (b) a first drawing unit for drawing the ground surface and the feature by executing depth determination by referring to the map database, and (c) a second drawing unit for drawing a target feature, which is a feature in which at least a part thereof is hidden by a ground surface or other features in the drawing by the first drawing unit, by overwriting the target feature on a drawing result by the first drawing unit by using the map data without executing depth determination with respect to the drawing result by the first drawing unit.

Abstract: A three-dimensional map is displayed in a bird's eye view with a stereoscopic effect of feature polygons by providing shading in an appropriate direction according to the gaze direction in a simulative manner. Shading wall polygons are set in addition to feature polygons in three-dimensional map data. The shading wall polygon is a virtual plate-like polygon provided vertically, for example, along a boundary of a feature polygon. When provided around the water system, the shading wall polygon is specified to be opaque on one surface viewed from the water system side and to be transparent on the opposite surface. The shading wall polygons are drawn along with the feature polygons in the process of displaying a map. The shading wall polygon is drawn in black, gray or the like only at a location where the surface specified to be opaque faces a gaze direction.

Abstract: A map database stores three-dimensional polygons of features, as well as water system polygons such as sea and lake and ground surface polygons. The map database stores map data in multiple levels having different levels of details, such as levels LVa to LVc. A procedure of displaying a three-dimensional map offsets the water systems relative to the ground surfaces, draws a map of a distant view area distant away from the viewpoint using map data at a low level of details, subsequently clears a depth buffer and newly draws a map of a close view area close to the viewpoint using map data at a high level of details. The offset is set to increase in the distant view area and decrease in the close view area. Increasing the offset in the distant view area avoids the occurrence of Z-fighting in the distant area from the viewpoint.