| 摘要 |
PROBLEM TO BE SOLVED: To make properly correctable a distortion due to the difference of latitudes while preventing the plotting speed of a map from being lowered in tha case of plotting the map by using map data which are prepared by assuming an area enclosed with fixed latitude and longitude to be a rectangle or a square. SOLUTION: A distortion correction factor Hs in latitude of a detected present address is decided (S140) and the table of correction factors for coordinate transformation Ht in which the distortion correction factor Hs is multipied by sin values of rotational angles is prepared (S150). At the time of plotting a map, coordinate transformations of map data are performed by using the correction factors for map transformation Ht (S170). In short, coordinate values X, Y posterior to a coordinate transformation can be calculated with simple equations such as X=βx-αy, Y=αx+βy by using a correction factor for coordinate transformationαcorresponding to the sin value of the rotational angleθof the map and a correction factor for coordinate transformationβcorresponding to the cos value of the rotational angleθof the map. Thus, the plotting speed can be improved as compared with that in the conventional method in which a distortion correction factor Hs is decided at a plotting time and the multiplying processing of the correction factor Hs and the rotational angle of the map is performed. |
