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New function CDB_CreateOverviewsWithToleranceInPixels

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This function allows defining the previously fixed parameter grid_px.
The lim parameter used to define the reference Z level is also
correlated to this value.

Fixes #219
This commit is contained in:
Javier Goizueta
2016-04-04 19:21:10 +02:00
parent aff7ae3e2e
commit 57c32332e2
4 changed files with 55 additions and 25 deletions
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38
scripts-available/CDB_Overviews.sql
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@@ -266,15 +266,21 @@ $$ LANGUAGE PLPGSQL STABLE;
-- Parameters:
-- reloid: oid of the input table. It must be a cartodbfy'ed table.
-- Return value: Z level as an integer
CREATE OR REPLACE FUNCTION _CDB_Feature_Density_Ref_Z_Strategy(reloid REGCLASS)
CREATE OR REPLACE FUNCTION _CDB_Feature_Density_Ref_Z_Strategy(reloid REGCLASS, tolerance_px FLOAT8 DEFAULT NULL)
RETURNS INTEGER
AS $$
DECLARE
lim FLOAT8 := 500; -- TODO: determine/parameterize this
lim FLOAT8;
nz integer := 4;
fd FLOAT8;
c FLOAT8;
BEGIN
IF (tolerance_px IS NULL) OR tolerance_px = 0 THEN
lim := 500;
ELSE
lim := floor(power(256/tolerance_px, 2))/2;
END IF;
-- Compute fd as an estimation of the (maximum) number
-- of features per unit of tile area (in webmercator squared meters)
SELECT _CDB_Feature_Density(reloid, nz) INTO fd;
@@ -321,7 +327,7 @@ $$ LANGUAGE PLPGSQL IMMUTABLE;
-- ref_z Z level assigned to the original table
-- overview_z Z level of the overview to be generated, must be smaller than ref_z
-- Return value: Name of the generated overview table
CREATE OR REPLACE FUNCTION _CDB_Sampling_Reduce_Strategy(reloid REGCLASS, ref_z INTEGER, overview_z INTEGER)
CREATE OR REPLACE FUNCTION _CDB_Sampling_Reduce_Strategy(reloid REGCLASS, ref_z INTEGER, overview_z INTEGER, tolerance_px FLOAT8 DEFAULT NULL)
RETURNS REGCLASS
AS $$
DECLARE
@@ -332,6 +338,7 @@ AS $$
num_samples INTEGER;
BEGIN
overview_rel := _CDB_Overview_Name(reloid, ref_z, overview_z);
-- TODO: compute fraction from tolerance_px if not NULL
fraction := power(2, 2*(overview_z - ref_z));
-- FIXME: handle schema name for overview_rel if reloid requires it
@@ -547,14 +554,13 @@ $$ LANGUAGE PLPGSQL STABLE;
-- ref_z Z level assigned to the original table
-- overview_z Z level of the overview to be generated, must be smaller than ref_z
-- Return value: Name of the generated overview table
CREATE OR REPLACE FUNCTION _CDB_GridCluster_Reduce_Strategy(reloid REGCLASS, ref_z INTEGER, overview_z INTEGER)
CREATE OR REPLACE FUNCTION _CDB_GridCluster_Reduce_Strategy(reloid REGCLASS, ref_z INTEGER, overview_z INTEGER, grid_px FLOAT8 DEFAULT NULL)
RETURNS REGCLASS
AS $$
DECLARE
overview_rel TEXT;
reduction FLOAT8;
base_name TEXT;
grid_px FLOAT8 = 7.5; -- Grid size in pixels at Z level overview_z
grid_m FLOAT8;
aggr_attributes TEXT;
attributes TEXT;
@@ -572,6 +578,11 @@ AS $$
overview_rel := _CDB_Overview_Name(reloid, ref_z, overview_z);
-- Grid size in pixels at Z level overview_z
IF grid_px IS NULL THEN
grid_px := 7.5;
END IF;
-- compute grid cell size using the overview_z dimension...
SELECT CDB_XYZ_Resolution(overview_z)*grid_px INTO grid_m;
@@ -647,6 +658,19 @@ $$ LANGUAGE PLPGSQL;
CREATE OR REPLACE FUNCTION CDB_CreateOverviews(reloid REGCLASS, refscale_strategy regproc DEFAULT '_CDB_Feature_Density_Ref_Z_Strategy'::regproc, reduce_strategy regproc DEFAULT '_CDB_GridCluster_Reduce_Strategy'::regproc)
RETURNS text[]
AS $$
DECLARE
tolerance_px FLOAT8;
BEGIN
-- Use the default tolerance
tolerance_px := 2.0;
RETURN CDB_CreateOverviewsWithToleranceInPixels(reloid, tolerance_px, refscale_strategy, reduce_strategy);
END;
$$ LANGUAGE PLPGSQL;
-- Create overviews with additional parameter to define the desired detail/tolerance in pixels
CREATE OR REPLACE FUNCTION CDB_CreateOverviewsWithToleranceInPixels(reloid REGCLASS, tolerance_px FLOAT8, refscale_strategy regproc DEFAULT '_CDB_Feature_Density_Ref_Z_Strategy'::regproc, reduce_strategy regproc DEFAULT '_CDB_GridCluster_Reduce_Strategy'::regproc)
RETURNS text[]
AS $$
DECLARE
ref_z integer;
overviews_z integer[];
@@ -657,7 +681,7 @@ DECLARE
overviews_step integer := 1;
BEGIN
-- Determine the referece zoom level
EXECUTE 'SELECT ' || quote_ident(refscale_strategy::text) || Format('(''%s'');', reloid) INTO ref_z;
EXECUTE 'SELECT ' || quote_ident(refscale_strategy::text) || Format('(''%s'', %s);', reloid, tolerance_px) INTO ref_z;
-- Determine overlay zoom levels
-- TODO: should be handled by the refscale_strategy?
@@ -671,7 +695,7 @@ BEGIN
base_z := ref_z;
base_rel := reloid;
FOREACH overview_z IN ARRAY overviews_z LOOP
EXECUTE 'SELECT ' || quote_ident(reduce_strategy::text) || Format('(''%s'', %s, %s);', base_rel, base_z, overview_z) INTO base_rel;
EXECUTE 'SELECT ' || quote_ident(reduce_strategy::text) || Format('(''%s'', %s, %s, %s);', base_rel, base_z, overview_z, tolerance_px) INTO base_rel;
IF base_rel IS NULL THEN
EXIT;
END IF;