Bird's-eye view forming method, map display apparatus and navigation system

Abstract

In a navigation system using a bird's-eye view display mode, map data on a plan view map are subjected to a perspective projection conversion to obtain drawing data on a bird's-eye view map. In this case, an input of the position of a view point is accepted, and a projection plane for a bird's-eye view is determined on the basis of the coordinates of a current position and a destination and the position of the view point so that the display positions of the two points which have been subjected to perspective-projection conversion are coincident with predetermined positions. Alternatively, an input of a scale is accepted, and the position of the view point and the projection plane are determined on the basis of the coordinates of the two points and the scale so that the display positions of the two points after the perspective projection conversion are coincident with predetermined positions and the drawing scale is coincident with the input scale. Or, as a further alternative, an input of the projection angle is accepted, and the projection plane is determined on the basis of the projection angle and the position of the view point.

What is claimed is:  
     
         1 . A map display apparatus comprising: 
 an image display device;    map storage means for storing map data to display maps; and    map drawing means for preparing drawing data of a map using said map data read out from said map storage means and displaying an image of the map on said image display device on the basis of the drawing data, wherein said map drawing means includes coordinate transforming means for transforming coordinate data contained in the map data, and said coordinate transforming means includes perspective projection means for perspectively projecting the coordinate data contained in the map data onto a predetermined projection plane with a view point at a desired position to thereby prepare the drawing data of a bird's-eye view.    
     
     
         2 . The map display apparatus as claimed in  claim 1 , further comprising an input device, wherein said coordinate transforming means further includes means for accepting an input of the position of the view point through said input device, and means for determining the projection plane on the basis of predetermined two points contained in the map data and the input view point position so that the drawing positions of the two points after the perspectively projecting operation are coincident with predetermined positions.  
     
     
         3 . The map display apparatus as claimed in  claim 1 , further comprising an input device, and wherein said coordinate transforming means further includes means for accepting an input of a scale through said input device, and means for determining the position of the view point and the projection plane on the basis of the coordinates of two predetermined points contained in the map data and the input scale so that the drawing positions of the two points after the perspectively projecting operation are coincident with predetermined positions, and the scale of a drawn map on the projection plane is coincident with the input scale.  
     
     
         4 . The map display apparatus as claimed in  claim 1 , further comprising an input device, and wherein said coordinate transforming means further includes means for accepting, through said input device, an input of a projection angle which is an intersection angle between the projection plane and a plane on which the map data are defined, and means for determining the projection plane on the basis of the input projection angle and the position of the view point.  
     
     
         5 . The map display apparatus as claimed in  claim 1 , further comprising means for preparing drawing data of a plan view without performing the perspective projection processing, and drawing determining means for determining one of the bird's-eye view and the plan view for which the drawing data should be prepared.  
     
     
         6 . The map display apparatus as claimed in  claim 5 , further comprising an input device, and wherein said coordinate transforming means further includes drawing selection accepting means for accepting, through said input device, an instruction indicating one of the bird's-eye view and the plan view for which the drawing data are prepared, and wherein said drawing determining means determines the drawing data to be prepared in accordance with the accepted instruction of said drawing selection accepting means.  
     
     
         7 . The map display apparatus as claimed in  claim 5 , wherein said map drawing means further includes projection angle changing means for instructing said coordinate transforming means to prepare drawing data of at least one second bird's-eye view to be obtained through the perspective projection using a second projection angle which is smaller than a first projection angle corresponding to the projection angle to obtain a first bird's-eye view, and instructing said image display device to display a map image with the drawing data of the second bird's-eye view between the first bird's-eye view display obtained through the perspective projection using the first projection angle and the plan view display, in a case where a display target for which the drawing data are to be prepared is changed from one of the first bird's-eye view and the plan view to the other.  
     
     
         8 . The map display apparatus as claimed in  claim 7 , wherein said projection angle changing means includes means for preparing drawing data of two or more said second bird's-eye views by using two or more said second projection angles which  5  are different from each other, wherein when the display target is changed from the bird's-eye view to the plan view, said projection angle changing means successively displays the two or more second bird's-eye views in a projection-angle order from a larger projection angle to a smaller projection angle, and when the display target is changed from the plan view to the bird's eye view, said projection angle changing means successively displays the two or more second bird's-eye view in a projection-angle order from a smaller projection angle to a larger projection angle.  
     
     
         9 . The map display apparatus as claimed in  claim 6 , wherein said map drawing means further includes means for accepting an indication of any point contained in the map data through said input device, and wherein said drawing determining means determines the drawing data of the plan view as the drawing data to be prepared when accepting the indication of the point.  
     
     
         10 . The map display apparatus as claimed in  claim 1 , wherein the map data contain, as character string data, vector data to recognize the position of a character string, and image data to recognize an image of the character string, and said coordinate transforming means performs no perspective projection on the image data of the map data.  
     
     
         11 . The map display apparatus as claimed in  claim 1 , wherein said map drawing means further includes drawing judgment means for determining whether data of at least one node contained in the drawing data should be set as one of a number of drawing targets, and eliminating said data of a node which is not set as a drawing target from the drawing targets, and wherein said map drawing means displays a map image on said image display device with the drawing data which have been processed by said drawing judgment means.  
     
     
         12 . The map display apparatus as claimed in  claim 11 , wherein when the data of the node are data of a character string, the judgment of said drawing judgment means is based on a judgment as to whether the display height of the character string from the bottom side of a display frame after the perspective projection is equal to or less than a predetermined reference value on the display frame.  
     
     
         13 . The map display apparatus as claimed in  claim 12 , wherein the reference value is equal to “⅔” from the bottom side of the display frame when the display height (size) of the display frame is set to “1”.  
     
     
         14 . The map display apparatus as claimed in  claim 11 , wherein when the data of the node are data of a character string, the judgment of said drawing judgment means is based on a judgment as to whether the distance between the visual-point position and the position at which the character string is defined in the map data is equal to or less than a predetermined reference value.  
     
     
         15 . The map display apparatus as claimed in  claim 11 , wherein when the data of the node are data of a character string, the judgment of said drawing judgment means is based on a judgment as to whether the distance between a predetermined point contained in the map and the position at which the character string is defined in the map data is equal to or less than a predetermined reference value.  
     
     
         16 . The map display apparatus as claimed in  claim 11 , wherein an attribute is beforehand allocated to at least a part of each node, and said drawing judgment means sets, as a drawing target, data of a node having an attribute which meets a preset attribute allocated to each display area on the display frame, and eliminates from the drawing targets data of a node having an attribute which does not meet the preset attribute.  
     
     
         17 . The map display apparatus as claimed in  claim 1 , wherein said coordinate transforming means changes the projection angle in accordance with the distance between two predetermined points contained in the map data.  
     
     
         18 . The map display apparatus as claimed in  claim 17 , wherein said coordinate transforming means reduces the projection angle to a smaller value as the distance between the two points becomes shorter.  
     
     
         19 . The map display apparatus as claimed in  claim 1 , wherein the map data contain data of character strings, and said map drawing means further includes means for setting a display priority rank for the character strings, and character string rearranging means for displaying a character string having the highest display priority rank of character strings when the display positions of said character strings are overlapped with one another.  
     
     
         20 . The map display apparatus as claimed in  claim 19 , wherein the display priority rank of a character string is set in accordance with the display height of the character string on the display frame from the bottom side of the display frame.  
     
     
         21 . The map display apparatus as claimed in  claim 20 , wherein the display priority rank of a character string is set to be higher as the display height of the character string on the display frame from the bottom side of the display frame becomes lower.  
     
     
         22 . The map display apparatus as claimed in  claim 19 , wherein the display priority rank of a character string is set in accordance with the distance between a predetermined point contained in the map data and a point at which the character string is defined.  
     
     
         23 . The map display apparatus as claimed in  claim 22 , wherein the display priority rank is set to be higher as the distance between the predetermined point and the point at which the character string is defined becomes shorter.  
     
     
         24 . A map display apparatus comprising an image display device, map storing means for storing map data to display a map, and map drawing means for preparing drawing data of said map by using said map data read out from said map storing means and displaying a map image on said image display device on the basis of the drawing data, wherein the map data contain data of character strings, and wherein said map drawing means includes means for setting display priority ranks of the character strings, and character rearranging means for displaying a character string having the highest display priority rank of overlapped character strings when the display positions of said character strings are overlapped with one another on a display map.  
     
     
         25 . A navigation system comprising an image display device, map storing means for storing map data to display a map, map drawing means for preparing drawing data of said map by using said map data read out from said map storing means and displaying a map image on said image display device on the basis of the drawing data, and current position recognizing means for recognizing a current position, wherein said map drawing means includes coordinate transforming means for transforming coordinate data contained in the map data, and said coordinate transforming means includes perspective projection means for perspectively projecting the coordinate data contained in the map data onto a predetermined projection plane with a view point at a desired position, to thereby prepare the drawing data of a bird's-eye view.  
     
     
         26 . The navigation system as claimed in  claim 25 , further comprising an input device, wherein said coordinate transforming means further includes means for accepting an input of the position of the view point through said input device, and means for determining the projection plane on the basis of predetermined two points contained in the map data and the input view point position so that the drawing positions of the two points after the perspectively projecting operation are coincident with predetermined positions.  
     
     
         27 . The navigation system as claimed in  claim 26 , wherein one of said two points is the current position which is recognized by said current position recognizing means.  
     
     
         28 . The navigation system as claimed in  claim 25 , further comprising an input device, wherein said coordinate transforming means further includes means for accepting an input of a scale through said input device, and means for determining the position of the view point and the projection plane on the basis of the coordinates of predetermined two points contained in the map data and the input scale so that the drawing positions of the two points after the perspectively projecting operation are coincident with predetermined positions, and the scale of a drawn map on the projection plane is coincident with the input scale.  
     
     
         29 . The navigation system as claimed in  claim 28 , wherein one of the two points is the current position which is recognized by said current position recognizing means.  
     
     
         30 . The navigation system as claimed in  claim 25 , further comprising an input device, wherein said coordinate transforming means changes the projection angle in accordance with the distance between the current position recognized by said current position recognizing means and a destination which is indicated through said input device.  
     
     
         31 . The navigation system as claimed in  claim 25 , wherein the map data contain data of a character string, and said map drawing means further includes drawing judgment means for judging whether said data of said character string contained in the drawing data should be set as one of a number of drawing targets, on the basis of the distance between a point at which the character string is defined in the map data and a point on the map data which corresponds to the current position recognized by said current position recognizing means, and eliminating said data of the character string which are judged not to be set as a drawing target from the drawing targets, and wherein said map drawing means displays a map image on said image display device on the basis of the drawing data which have been processed by said drawing judgment means.  
     
     
         32 . The navigation system as claimed in  claim 25 , wherein the map data contain data of a character string, and said map drawing means further includes means for setting display priority ranks for each said character strings, and character string rearranging means for displaying said character string having the highest display priority rank of overlapped character strings when the display positions of character strings are overlapped with one another on the display frame, and wherein the display priority rank of said character string is set in accordance with the distance between a point on the map which corresponds to the current position recognized by said current position recognizing means and the point at which the character string is defined.  
     
     
         33 . The navigation system as claimed in  claim 25 , wherein said coordinate transforming means further includes means for determining the view point or the projection angle and the projection plane so that a height of a display position of the current position recognized by said current position recognizing means from a bottom side of a display frame is equal to or less than “⅓” when the height of the display frame is set to “1”.  
     
     
         34 . A bird's-eye view forming method for preparing drawing data of a map represented in a bird's-eye view display mode with map data, characterized in that coordinate data contained in the map data are perspectively projected onto a predetermined projection plane with a view point at a desired position to thereby prepare the drawing data of a bird's-eye view.  
     
     
         35 . The bird's-eye view forming method as claimed in  claim 34 , comprising the steps of: 
 accepting an input of the position of the view point; and    determining the projection plane on the basis of the coordinates of predetermined two points contained in the map data and the input position of the view point so that the drawing positions of the two points after the perspective projection are coincident to predetermined positions.    
     
     
         36 . The method as claimed in  claim 34 , comprising the steps of: 
 accepting an input of a scale; and    determining the position of the view point and the projection plane on the basis of the coordinates of predetermined two points contained in the map data and the input scale so that the drawing positions of the two points after the perspective projection are coincident with predetermined positions, and the scale of a drawn map on the projection plane is coincident with the input scale.    
     
     
         37 . The method as claimed in  claim 34 , comprising the steps of: 
 accepting an input of a projection angle which is an intersection angle between the projection plane and a plane on which the map data are defined; and    determining the projection plane on the basis of the input projection angle and a position of the view point.