Background map support defaults on Hakunapi item and items HTML pages

[teezip]

This issue describes expected background map projection on collections/{collection}/items/ and collections/{collection}/items/{id} pages.

Related to #199 if refactoring HTML packages (see also comments below on this issue).

Generic services published using Hakunapi

OpenStreetMap currently used as default (for example https://tile.openstreetmap.org/13/4671/2305.png) and this should be the default behaviour.

NLS of Finland specific services published using Hakunapi

Choices on NLS of Finland specific services with sample tiles:

• avoin-karttakuva.maanmittauslaitos.fi/avoin/wmts/1.0.0/taustakartta/default/ETRS-TM35FIN/8/123/123.png
• avoin-karttakuva.maanmittauslaitos.fi/avoin/wmts/1.0.0/taustakartta/default/WGS84_Pseudo-Mercator/13/2305/4671.png

Background map projected as WGS84_Pseudo-Mercator should be used when selecting either CRS:84, CRS:84h, EPSG:4326, EPSG:3857, EPSG:4258, EPSG:10690, EPSG:10689 or EPSG:10692 on the user interface.

Background map projected as ETRS-TM35FIN should be used on other cases (coordinate reference systems supported by NLS of Finland services.)

About those new codes not yet used in NLS of Finland services but are coming:

• 10690 : EUREF-FIN (lat, lon) - to be replacing 4258 in the future
• 10689 : EUREF-FIN + ellipsoidal height - maybe not coming very soon tough (cannot provide ellipsoidal height from N2000 easily on the fly)
• 10692 : EUREF-FIN + N2000 height - support for this is needed in some point

[teezip]

See also HTML page with Open Layers based background map interface implemented by a community module.

Source code: https://github.com/nls-jajuko/hakunapi-html-npm-openlayers

demo:
https://kauppahintatilasto.nls.fi/tilastopalvelu/features/1.1/collections/pno_hakuna_2026/items?crs=http%3A%2F%2Fwww.opengis.net%2Fdef%2Fcrs%2FEPSG%2F0%2F3883#0.12/64.8/24.6

In version 2.1.0 this should be analyzed whether to use OpenLayers based instead of Leaflet in Hakunapi core packages.