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 > <https://www.linkedin.com/company/niwa> Twitter > <https://twitter.com/niwa_nz> Instagram > <https://www.instagram.com/niwa_science> YouTube > <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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