Map rendering for navigation systems

Abstract

When map data is to be processed for display in a mapping or navigation apparatus, the application processor of the apparatus first checks to see whether any existing data in a local cache memory represents a similar map part to the new data that is to be processed. This is done by means of a similarity analysis. If the map data already in the cache is determined to be sufficiently similar to the map data that is to be displayed, new map data from a main map storage is not loaded and processed, but instead the existing data in the cache is processed for display of the map part in question. This has the benefit of a reduced system load, since already processed data does not need to be reloaded and reprocessed.

1 - 16 . (canceled) 
     
     
         17 . A method of rendering a map for display on a mapping or navigation apparatus, in which the map is rendered for display by loading data representing particular parts of the map to be displayed from a main map data store for processing and for display by a rendering processor of the mapping or navigation apparatus and the rendering processor of the mapping or navigation apparatus has a local memory in which data representing particular parts of a map to be displayed can be stored, the method comprising:
 determining whether a part of the map for which data is already stored in the local memory is similar to a new part of the map to be processed, when a part of the map is to be processed by the rendering processor for display; and   re-using data for the existing part of the map stored in the local memory for the rendering processor for displaying the new part of the map, upon the determination that a part of the map for which data is already stored in the local memory for the rendering processor is sufficiently similar to the new part of the map to be processed.   
     
     
         18 . The method of  claim 17 , wherein the stored map data is in the form of a library of base map display elements, wherein the map display elements may then be used to reproduce a desired map or maps, and the method comprises:
 assessing the similarity between one or more map display elements already stored in the local memory for the rendering processor and a new map display element or elements to be processed, and then loading and processing a new map display element or elements or reusing a map display element or elements that is already stored in the local memory for the rendering processor on the basis of the similarity assessment.   
     
     
         19 . The method of  claim 17 , wherein the similarity determination uses a function that calculates a relative error between the already stored map part and the new map part and then determines whether the relative error is below a selected threshold value or not. 
     
     
         20 . The method of  claim 19 , wherein the relative error is determined using a root mean squared error (RMSE) between the already stored map part and the new map part. 
     
     
         21 . The method of  claim 17 , wherein the stored map data includes meta information that can be used to determine how similar respective parts of the map are. 
     
     
         22 . The method of  claim 17 , wherein the similarity determination is configured to take account of run time parameters. 
     
     
         23 . The method of  claim 17 , wherein the similarity determination is dependent upon the distance from a viewer of the map part that is to be displayed. 
     
     
         24 . The method of  claim 17 , wherein the similarity determination further includes determining a transformation to apply to the map part already stored in the local memory in order for the rendering processor to compensate for misalignment between the map parts being considered. 
     
     
         25 . The method of  claim 24 , wherein the applied transformation is based on a comparison of contributing components of the map part in the local memory to corresponding components of the new map part to be displayed. 
     
     
         26 . The method of  claim 17 , further comprising displaying the map on a mapping or navigation apparatus. 
     
     
         27 . A mapping or navigation apparatus, comprising:
 a display for displaying a digital map to a user;   a rendering processor configured to process digital map data and cause a digital map to be displayed on the display; and   a local memory for use by the rendering processor in which data representing particular parts of the map to be displayed can be stored, and in which:   a map is rendered for display by loading data representing particular parts of the map to be displayed from a main map data store for processing for display by the rendering processor, and wherein the rendering processor is operable to:   determine whether a part of the map for which data is already stored in the local memory for the rendering processor is similar to a new part of the map to be processed, when data representing a part of a map is to be processed by the rendering processor for display; and   use data for an existing part of the map stored in the local memory for the rendering processor for displaying the new part of the map, upon the determination that a part of the map for which data is already stored in the local memory for the rendering processor is sufficiently similar to the new part of the map to be processed.   
     
     
         28 . The apparatus of  claim 27 , wherein the stored map data is in the form of a library of base map display elements, which elements can then be used to reproduce a desired map or maps, and wherein the rendering processor is operable to:
 determine whether a part of the map for which data is already stored in the local memory for the rendering processor is similar to the new part of the map to be processed by assessing the similarity between one or more map display elements already stored in the local memory for the rendering processor and a new map display element or elements to be processed; and   re-use data for an existing part of the map stored in the local memory for the rendering processor for displaying the new part of the map by loading and processing a new map display element or elements or reusing a map display element or elements that is already stored in the local memory for the rendering processor on the basis of the similarity assessment, upon a determination that a part of the map for which data is already stored in the local memory for the rendering processor is sufficiently similar to the new part of the map to be processed.   
     
     
         29 . The apparatus of  claim 27 , wherein the similarity determination uses a function that calculates a relative error between the already stored map part and the new map part and then determines whether the relative error is below a selected threshold value or not. 
     
     
         30 . The apparatus of  claim 29 , wherein a relative error margin increases as the distance from the viewer of the map part that is to be displayed increases. 
     
     
         31 . The apparatus of  claim 27 , wherein the stored map data includes meta information that can be used to determine how similar respective parts of the map are. 
     
     
         32 . The apparatus of  claim 27 , wherein the determination of whether a part of the map for which data is already stored in the local memory for the rendering processor is similar to the new part of the map to be processed is configured to take account of run time parameters. 
     
     
         33 . The apparatus of  claim 27 , wherein the similarity determination further includes determining a transformation to apply to the map part already stored in the local memory in order for the rendering processor to compensate for misalignment between the map parts being considered. 
     
     
         34 . The apparatus of  claim 27 , wherein the apparatus is a portable navigation device (PND) or an integrated navigation system. 
     
     
         35 . The apparatus of  claim 27 , wherein the apparatus displays the map on the display of the mapping or navigation apparatus. 
     
     
         36 . A non-transitory computer-readable medium comprising computer readable instructions which, when executed on one or more processors, cause the one or more processors to perform a method of rendering a map for display on a mapping or navigation apparatus, in which the map is rendered for display by loading data representing particular parts of the map to be displayed from a main map data store for processing and for display by a rendering processor of the mapping or navigation apparatus and the rendering processor of the mapping or navigation apparatus has a local memory in which data representing particular parts of a map to be displayed can be stored, the method comprising:
 determining whether a part of the map for which data is already stored in the local memory is similar to a new part of the map to be processed, when a part of the map is to be processed by the rendering processor for display; and   re-using data for the existing part of the map stored in the local memory for the rendering processor for displaying the new part of the map, upon the determination that a part of the map for which data is already stored in the local memory for the rendering processor is sufficiently similar to the new part of the map to be processed.