sorry I ask chatGPT to make hexagons size constant, this is its code :
I precise that I ask it to make circles and squares too
backend :
<?php
header('Content-Type: application/json');
// Connexion Redis
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$redis->auth('your_strong_password');
// Connexion PostgreSQL
$pdo = new PDO("pgsql:host=localhost;dbname=database", "user", "password", [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
]);
$shape = $_GET['shape'] ?? 'hexagone';
$bbox = explode(',', $_GET['bbox']);
$size = $_GET['size'] ?? 1000;
$radius = $_GET['radius'] ?? 500;
$resolution = $_GET['resolution'] ?? 8;
$zoom = $_GET['zoom'] ?? 2;
$cacheKey = "$shape:" . implode('-', $bbox) .
":$size:$radius:$resolution:$zoom";
// Vérifier le cache Redis
if ($redis->exists($cacheKey)) {
echo $redis->get($cacheKey);
exit;
}
list($minLng, $minLat, $maxLng, $maxLat) = $bbox;
$params = [':minLng' => $minLng, ':minLat' => $minLat, ':maxLng' =>
$maxLng, ':maxLat' => $maxLat];
if ($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'] = $resolution;
} elseif ($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;
} 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;
}
$stmt = $pdo->prepare($sql);
$stmt->execute($params);
$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
// Mise en cache Redis (10 minutes)
$redis->setEx($cacheKey, 600, json_encode($result));
echo json_encode($result);
frontend :
<!DOCTYPE html>
<html lang="fr">
<head>
<meta charset="UTF-8">
<title>Cartographie Dynamique (PHP + jQuery)</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;
let currentShape = 'hexagone';
function getColor(count) {
return count > 100 ? '#800026' :
count > 50 ? '#BD0026' :
count > 20 ? '#E31A1C' :
count > 10 ? '#FC4E2A' :
'#FFEDA0';
}
function fetchData() {
const bounds = map.getBounds();
const bbox =
`${bounds.getWest()},${bounds.getSouth()},${bounds.getEast()},${bounds.getNorth()}`;
const zoom = map.getZoom();
$.getJSON(`backend.php?shape=${currentShape}&bbox=${bbox}&size=1000&radius=500&resolution=8&zoom=${zoom}`,
function (data) {
if (layer) map.removeLayer(layer);
layer = L.geoJSON(data.map(item => JSON.parse(item.shape ||
item.h3_cell)), {
style: (feature) => ({
color: getColor(feature.properties?.point_count || 0),
weight: 2,
fillOpacity: 0.5
})
}).addTo(map);
});
}
$("#shapeSelector").change(function () {
currentShape = $(this).val();
fetchData();
});
map.on('moveend zoomend', fetchData);
fetchData();
</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 20:59, Sylvain Ard <sylvain....@gmail.com> a écrit :
> 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
> <http://tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.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
>>> <https://www.facebook.com/nzniwa> LinkedIn
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>>> <https://www.youtube.com/channel/UCJ-j3MLMg1H59Ak2UaNLL3A> To ensure
>>> compliance with legal requirements and to maintain cyber security
>>> standards, NIWA's IT systems are subject to ongoing monitoring, activity
>>> logging and auditing. This monitoring and auditing service may be provided
>>> by third parties. Such third parties can access information transmitted to,
>>> processed by and stored on NIWA's IT systems.
>>> Note: This email is intended solely for the use of the addressee and may
>>> contain information that is confidential or subject to legal professional
>>> privilege. If you receive this email in error please immediately notify the
>>> sender and delete the email.
>>>
>>
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