Add polygon simplification

New query string parameter polygon_threshold=<0.0..1> is introduced.
The float value of this parameter (defaults to 0) is passed to
ST_SimplifyPreserveTopology() on geometry we're about to output in
one (or many) requested formats such as GeoJSON, KML, etc.

This is useful when getting border polygons for whole countries, but
rendering them at large scale, when most of the high resolution details
cannot be seen anyway.  For example, the unsimplified polygon data for
Germany in GeoJSON format currently makes for about 3 MB response body.
With use of this new parameter, the application can greatly reduce the
amount of downloaded data and server response time while providing its
users with the same picture.  On a typical laptop screen resolution,
zooming out to fit the whole country borders on screen, only 1/100 amount
of details could be well enough.

diff --git a/lib/Geocode.php b/lib/Geocode.php
index 7bd4f55295513518794abbcc5e91405a3b2c9a69..a5454867c17939a9c6abd27486974d2014e7afdc 100644 (file)
--- a/lib/Geocode.php
+++ b/lib/Geocode.php
@@ -12,6 +12,7 @@
                protected $bIncludePolygonAsGeoJSON = false;
                protected $bIncludePolygonAsKML = false;
                protected $bIncludePolygonAsSVG = false;
+               protected $fPolygonSimplificationThreshold = 0.0;
 
                protected $aExcludePlaceIDs = array();
                protected $bDeDupe = true;
@@ -102,6 +103,11 @@
                        $this->bIncludePolygonAsSVG = $b;
                }
 
+               function setPolygonSimplificationThreshold($f)
+               {
+                       $this->fPolygonSimplificationThreshold = $f;
+               }
+
                function setDeDupe($bDeDupe = true)
                {
                        $this->bDeDupe = (bool)$bDeDupe;
@@ -1612,7 +1618,7 @@
                                        if ($this->bIncludePolygonAsKML) $sSQL .= ",ST_AsKML(geometry) as askml";
                                        if ($this->bIncludePolygonAsSVG) $sSQL .= ",ST_AsSVG(geometry) as assvg";
                                        if ($this->bIncludePolygonAsText || $this->bIncludePolygonAsPoints) $sSQL .= ",ST_AsText(geometry) as astext";
-                                       $sSQL .= " from placex where place_id = ".$aResult['place_id'];
+                                       $sSQL .= " from (select place_id,centroid,ST_SimplifyPreserveTopology(geometry,".$this->fPolygonSimplificationThreshold.") as geometry from placex where place_id = ".$aResult['place_id'].") as plx";
                                        $aPointPolygon = $this->oDB->getRow($sSQL);
                                        if (PEAR::IsError($aPointPolygon))
                                        {

diff --git a/website/search.php b/website/search.php
index a9e20d4eb47e564fa4889b42312869ecd8b3462e..ecf584ae97500d4d5f9a4f8368bb5c96029ad90c 100755 (executable)
--- a/website/search.php
+++ b/website/search.php
@@ -44,6 +44,8 @@
                $bAsKML = (boolean)isset($_GET['polygon_kml']) && $_GET['polygon_kml'];
                $bAsSVG = (boolean)isset($_GET['polygon_svg']) && $_GET['polygon_svg'];
                $bAsText = (boolean)isset($_GET['polygon_text']) && $_GET['polygon_text'];
+               $fThreshold = 0.0;
+               if (isset($_GET['polygon_threshold'])) $fThreshold = (float)$_GET['polygon_threshold'];
                if ( ( ($bAsGeoJSON?1:0)
                     + ($bAsKML?1:0)
                     + ($bAsSVG?1:0)
@@ -66,6 +68,7 @@
                $oGeocode->setIncludePolygonAsGeoJSON($bAsGeoJSON);
                $oGeocode->setIncludePolygonAsKML($bAsKML);
                $oGeocode->setIncludePolygonAsSVG($bAsSVG);
+               $oGeocode->setPolygonSimplificationThreshold($fThreshold);
        }
 
        $oGeocode->loadParamArray($_GET);