| | 490 | == '''Objective FV.20 - Being able to determine topological characteristics of a coverage''' == |
| | 491 | |
| | 492 | '''ST_HasOverlaps(rasttable text, rastcolumn text)'''[[BR]] |
| | 493 | '''ST_HasGaps(rasttable text, rastcolumn text)'''[[BR]] |
| | 494 | '''ST_HasTileSameSize(rasttable text, rastcolumn text)'''[[BR]] |
| | 495 | '''ST_HasTileAligned(rasttable text, rastcolumn text)'''[[BR]] |
| | 496 | '''ST_IsRegularlyTiled(rasttable text, rastcolumn text)''' if the four conditions above are fulfilled. The ST_HasTileSameSize() condition could be optional.[[BR]] |
| | 497 | |
| | 498 | ---- |
| | 499 | == '''Objective FV.21 - Being able to create overviews in SQL''' == |
| | 500 | |
| | 501 | '''ST_CreateOverviews(rasttable text, rastcolumn text, overviewnumber int)'''[[BR]] |
| | 502 | |
| | 503 | Creates the tiles corresponding to the lower resolution (or overviews) of a raster table. So that an overview table can be created like this: SELECT ST_CreateOverviews(rasttable, rast, 2); |
| | 504 | |
| | 505 | Pseudo code: |
| | 506 | |
| | 507 | IF ST_IsRegularlyTiled(rasttable text, rastcolumn text) THEN[[BR]] |
| | 508 | -- Check if the tiles can be divided into 2x2, 4x4, 8x8 [[BR]] |
| | 509 | IF 'SELECT ST_Width(rast) modulo 2 = (overviewnumber + 1) AND ST_Width(rast) modulo (overviewnumber + 1) = 0 FROM rasttable LIMIT 1'[[BR]] |
| | 510 | ST_Resample(all the tiles)[[BR]] |
| | 511 | Add a column with the number of the set of tile to union together[[BR]] |
| | 512 | ST_Union(using this number)[[BR]] |
| | 513 | ELSE[[BR]] |
| | 514 | Add a column with the number of the set of tile to union together[[BR]] |
| | 515 | ST_Union(using this number)[[BR]] |
| | 516 | ST_Resample(all the tiles)[[BR]] |
| | 517 | ELSE[[BR]] |
| | 518 | Resample(all the tiles) -- Without unioning them afterward[[BR]] |
| | 519 | END IF |
| | 520 | |
| | 521 | |
| | 522 | ---- |
