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Adjust overview coordinates to pixel centers

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This makes the adjustment for all grid sizes, not only
for integral number of pixels.
This commit is contained in:
Javier Goizueta 2016-04-25 13:33:43 +02:00
parent 580ec38ab8
commit 7b2100b51e
1 changed files with 12 additions and 5 deletions
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17
scripts-available/CDB_Overviews.sql
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@ -655,6 +655,10 @@ AS $$
pixel_m FLOAT8;
grid_m FLOAT8;
offset_m FLOAT8;
offset_x TEXT;
offset_y TEXT;
cell_x TEXT;
cell_y TEXT;
aggr_attributes TEXT;
attributes TEXT;
columns TEXT;
@ -694,12 +698,15 @@ AS $$
aggr_attributes := aggr_attributes || ', ';
END IF;
-- points are displaced to it's cell's center
offset_m := grid_m/2;
-- then corrected to be at the nearest pixel's center (by up to half a pixel)
offset_m := offset_m + pixel_m/2 - MOD((grid_m/2)::numeric, pixel_m::numeric)::float8;
-- Center of each cell:
cell_x := Format('gx*%1$s + %2$s', grid_m, grid_m/2);
cell_y := Format('gy*%1$s + %2$s', grid_m, grid_m/2);
point_geom := Format('ST_SetSRID(ST_MakePoint(gx*%1$s + %2$s, gy*%1$s + %2$s), 3857)', grid_m, offset_m);
-- Displacement to the nearest pixel center:
offset_x := Format('%2$s/2 - MOD((%1$s)::numeric, (%2$s)::numeric)::float8', cell_x, pixel_m);
offset_y := Format('%2$s/2 - MOD((%1$s)::numeric, (%2$s)::numeric)::float8', cell_y, pixel_m);
point_geom := Format('ST_SetSRID(ST_MakePoint(%1$s + %3$s, %2$s + %4$s), 3857)', cell_x, cell_y, offset_x, offset_y);
-- compute the resulting columns in the same order as in the base table
WITH cols AS (