this is the code of chatGPT with H3 :
backend :
<?php
header('Content-Type: application/json');
$pdo = new PDO("pgsql:host=localhost;dbname=database", "user", "password",
[PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]);
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$redis->auth('password');
$shape = $_GET['shape'];
$bbox = explode(',', $_GET['bbox']);
$size = $_GET['size'] ?? null;
$radius = $_GET['radius'] ?? null;
$resolution = $_GET['resolution'] ?? 8;
$cacheKey = "$shape:" . implode('-', $bbox) . ":$size:$radius:$resolution";
if ($redis->exists($cacheKey)) {
echo $redis->get($cacheKey);
exit;
}
if ($shape === "hexagone") {
$sql = "
SELECT h3_geo_to_h3(ST_Y(geom), ST_X(geom), :resolution) AS
h3_cell, COUNT(*) AS point_count
FROM your_points_table
WHERE geom && ST_MakeEnvelope(:minLng, :minLat, :maxLng, :maxLat,
4326)
GROUP BY h3_cell;
";
$params = [':resolution' => $resolution, ':minLng' => $bbox[0],
':minLat' => $bbox[1], ':maxLng' => $bbox[2], ':maxLat' => $bbox[3]];
} elseif ($shape === "cercle") {
$sql = "
SELECT ST_AsGeoJSON(ST_Buffer(geom::geography, :radius)::geometry)
AS shape, COUNT(*) AS point_count
FROM your_points_table
WHERE geom && ST_MakeEnvelope(:minLng, :minLat, :maxLng, :maxLat,
4326)
GROUP BY shape;
";
$params = [':radius' => $radius, ':minLng' => $bbox[0], ':minLat' =>
$bbox[1], ':maxLng' => $bbox[2], ':maxLat' => $bbox[3]];
} else {
$sql = "
SELECT ST_AsGeoJSON(ST_Envelope(ST_Buffer(geom::geography, :size,
'quad_segs=1')::geometry)) AS shape, COUNT(*) AS point_count
FROM your_points_table
WHERE geom && ST_MakeEnvelope(:minLng, :minLat, :maxLng, :maxLat,
4326)
GROUP BY shape;
";
$params = [':size' => $size, ':minLng' => $bbox[0], ':minLat' =>
$bbox[1], ':maxLng' => $bbox[2], ':maxLat' => $bbox[3]];
}
$stmt = $pdo->prepare($sql);
$stmt->execute($params);
$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
$redis->setEx($cacheKey, 3600, json_encode($result));
echo json_encode($result);
frontend :
<!DOCTYPE html>
<html lang="fr">
<head>
<meta charset="UTF-8">
<title>Cartographie avec Forme Sélectionnée</title>
<link rel="stylesheet" href="https://unpkg.com/leaflet/dist/leaflet.css
">
<script src="https://unpkg.com/leaflet/dist/leaflet.js";></script>
<script src="https://code.jquery.com/jquery-3.6.0.min.js";></script>
<style>
#map { height: 500px; width: 100%; }
</style>
</head>
<body>
<h2>Choisissez la forme :</h2>
<select id="shapeSelector">
<option value="hexagone">Hexagone</option>
<option value="cercle">Cercle</option>
<option value="carre">Carré</option>
</select>
<div id="map"></div>
<script>
const map = L.map('map').setView([0, 0], 2);
L.tileLayer('https://{s}.
tile.openstreetmap.org/{z}/{x}/{y}.png').addTo(map);
let layer;
function fetchData(shape) {
const bbox = "-10,-10,10,10";
const url =
`backend.php?shape=${shape}&bbox=${bbox}&size=1000&radius=500&resolution=8`;
$.getJSON(url, function (data) {
if (layer) map.removeLayer(layer);
layer = L.geoJSON(data, {
style: {
color: shape === "carre" ? "green" : shape === "cercle"
? "blue" : "red",
weight: 2,
fillOpacity: 0.4
}
}).addTo(map);
});
}
$("#shapeSelector").change(function () {
fetchData($(this).val());
});
fetchData("hexagone"); // Chargement initial
</script>
</body>
</html>
Sylvain Ard
0549507724
0778380991
sylvain....@gmail.com
https://www.sylvain-ard.fr <http://sylvain-ard.fr>
Entreprise individuelle SIRET : 80079243400022
Appt 26 Bât A Résidence Le Patio
83 rue de la Bugellerie
86000 Poitiers
Le ven. 14 mars 2025 à 20:49, Sylvain Ard <sylvain....@gmail.com> a écrit :
> yes but H3 can't simplify the job ?
> Sylvain Ard
> 0549507724
> 0778380991
> sylvain....@gmail.com
> https://www.sylvain-ard.fr <http://sylvain-ard.fr>
> Entreprise individuelle SIRET : 80079243400022
> Appt 26 Bât A Résidence Le Patio
> 83 rue de la Bugellerie
> 86000 Poitiers
>
>
> Le ven. 14 mars 2025 à 20:48, Brent Wood <brent.w...@niwa.co.nz> a écrit :
>
>> Hi,
>>
>> Off the top of my head...
>>
>> Postgis can easily cope with millions of records. Given the points are
>> there, use that to create the hexagons as required - this can be done using
>> https://postgis.net/docs/ST_HexagonGrid.html
>>
>> If you set up your QGIS project with preset zoom levels, and create a set
>> of appropriately sized hexagons for each zoom level, then populate a column
>> with the number of points it contains.
>>
>> There will be some devilish details - as you zoom in, the polygon's real
>> area will get smaller, so will contain less points. A fixed symbology will
>> therefore change the colour range with the scale.
>>
>> Calculating a normalised value, perhaps something like instead of the no
>> of points, you calculate a normalised value - the hex at each scale with
>> the most points gets 100, the rest get a value based on the no of
>> points/the max for that scale, so all polygon datasets will have colours
>> set to values between 0 and 100. All doable with SQL.
>>
>> Do all the data stuff in Postgis, then just plot in QGIS.
>>
>> There are various ways to set QGIS up for this, but one reasonably
>> straightforward way that should work is having a separate hexagon layer for
>> each scale, with a scale limit on displaying it so that all map scales are
>> represented by one of the hexagon layers, with the fixed zoom
>> levels/scales, set the same symbology for each layer, then group them into
>> a single group.
>>
>>
>> Something to consider anyway...
>>
>> Cheers
>>
>> Brent Wood
>>
>> Principal Technician, Fisheries
>> NIWA
>> DDI: +64 (4) 3860529
>> ------------------------------
>> *From:* QGIS-User <qgis-user-boun...@lists.osgeo.org> on behalf of
>> Sylvain Ard via QGIS-User <qgis-user@lists.osgeo.org>
>> *Sent:* Friday, March 14, 2025 23:35
>> *To:* qgis-user@lists.osgeo.org <qgis-user@lists.osgeo.org>
>> *Subject:* [Qgis-user] question
>>
>> Hello,
>> I'd like a map with hexagons that are darker the more points there are
>> underneath. My points are in a PostgreSQL table. If there are no points,
>> there should be no hexagon. The hexagons have a constant size on the
>> screen, so they have to be recalculated each time the map is zoomed in. I
>> want a truly optimized solution because I have millions of points. So,
>> perhaps I could use QGIS-server.
>> Please suggest a solution for both the server and client side.
>> Best regards
>> PS : my map must be like GBIF maps
>>
>> Sylvain Ard
>> 0549507724
>> 0778380991
>> sylvain....@gmail.com
>> https://www.sylvain-ard.fr <http://sylvain-ard.fr/>
>> Entreprise individuelle SIRET : 80079243400022
>> Appt 26 Bât A Résidence Le Patio
>> 83 rue de la Bugellerie
>> 86000 Poitiers
>> <https://www.niwa.co.nz/>
>> Brent Wood
>> Principal Technician - GIS and Spatial Data Management
>> Programme Leader - Environmental Information Delivery
>> +64-4-386-0529
>>
>> National Institute of Water & Atmospheric Research Ltd (NIWA)
>> 301 Evans Bay Parade Hataitai Wellington New Zealand
>> *Connect with NIWA:* niwa.co.nz <https://www.niwa.co.nz/> Facebook
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>>
>
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