摘要 |
Methods and apparatuses to generate and to access compressed and indexed elevations of Digital Elevation Models. In one aspect of the invention, a method to store elevation data includes: compressing elevation data of a fir st portion of a Digital Elevation Model (DEM) to generate first compressed elevation data; storing the first compressed elevation data in a storage location pointed to by a first index; and storing the first index. In anothe r aspect of the invention, a method to retrieve elevation data includes: locating a first compressed portion of a Digital Elevation Model (DEM) using a first index; and decompressing the first compressed portion to retrieve firs t elevation data for at least one sample point in the Digital Elevation Model. The Digital Elevation Model has a plurality of compressed portions which includes the first compressed portion; and the first index points to a stora ge location where the first compressed portion is stored. |