| Input: The dynamic error of view-dependent , |
| data scale of current data of scene , data |
| position: longitude LONG, latitude LAT. |
| Output: Pre-fetch data set , and load file mapping buffer. |
| Description of function: Locate physical data block, and |
| load data buffer in memory through the threshold of screen |
| error and the position of scene, as the requirement of |
| the amount of data in memory. |
| (1) Initialization: Clear data set . |
| (2) Traverse the head file of data source (physical model), |
| and determine which data block belongs to it |
| according to (LONG, LAT), meanwhile, record the number of involved files. |
| (3) For each file from to fileN, do the process as follows: |
| //If it is a single file, then execute once, |
| otherwise, execute more than once |
| (3.1) According to and Formula (2), compute the error |
| threshold needed by current scene. |
| (3.2) Get cluster , and let the arrangement of static error |
| thresholds of be: , |
| , determine which interval belongs to, |
| and define the cluster which meets the requirements as . |
| (3.3) If is less than fileN, then go to step 3. |
| (4) According to the moving direction of viewpoint, update the |
| value of LONG and LAT, and establish fileN file mapping buffers. |
| (5) If fileN is 1, then determine the initial position of |
| (according to LONG, LAT), and intercept data block . |
| (6) If fileN is greater than 1, then determine the position |
| of cluster , and let be , and fileN: |
| (6.1) Judge the relation of the file of two adjacent data block |
| (as Figures 5(b), 5(c), and 5(e)); |
| (6.2) Distribute data blocks in , and form . |
| According to the position relation Z-shape filling adjacent |
| data block cluster after that. |
| (7) If the intersection of and the existed data in data |
| buffer is empty, then load , otherwise load , |
| namely load data incrementally. |
| (8) The end. |
