[Geoserver-devel] Supporting zoom levels in CSS, sharing some YSLD code

GeoServer GeoServer Developer
1

Hi,
first of all, apologies for the cross post, I’ve done it because the refactor I’m proposing concerns both projects.

I want to add zoom level support in CSS, with a familiar syntax like [@z = 10] or [@z >= 15],
and an eventual tile matrix set choice as a top level directive like @tms “myCustomTileMatrixSet”.

In order to do so, I’ll need to convert zoom levels to scale denominators, and look up configured tile
matrix sets in GeoServer. YSLD has this problem basically already solved, with a set of interfaces and
classes that have apparently nothing YSLD specific:

  • ZoomContext, describing relationships between zoom levels and scale denominators (e.g., part of what a TileMatrixSet does)
  • ZoomContextFinder, to lookup up ZoomContext by name
  • GWCZoomContextFinder, to look up specifically GWC configured Tile Matrix Set objects.

I would like to propose the following refactoring, to reuse the same work in the CSS parser

Step 1, move the the ZoomContext* classes to gt-main, inside a new org.geotools.styling.zoom package
(I’ve checked, it’s not taken).

Step 2, move the GWCZoomContextFinder into the GWC module, again for sharing purposes.

Then I will be able to use the same functionality from the CSS modules.
As an added bonus, I’d like to refactor the gs-ysld module so that it does not depend on the GWC presence,
as a deploy might use alternative style languages in WMS, without having tile caching embedded in the same process (e.g., GeoServer Cloud).
The code will look up a ZoomContextFinder using GeoServerExtensions, and if not found, use the DefaultZoomContextFinder instead.

If there are no objections, I’ll move on with the refactor next week.

···

Regards,

Andrea Aime

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2

This sounds good to me, is there a possibility that it will allow zoom level to become available in SLD as a vendor option or special variable? I’m not suggesting that you do that now but it would be nice if it is possible for future implementations, though I’m not promising that I’ll ever get around to it.

Ian

···

Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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Ian Turton

3

Hi Ian,
once we have support for TileMatrixSet definitions generally available in gt-main, there are a multiplicity of module that
can use them, for example, I was also considering features-pregeneralized to be also a good candidate.

Going to SLD, of course one could leverage the zoom to scale mapping, I believe it’s more a matter of agreeing on how that
would be done. A dedicated set of tags (MinZoom, MaxZoom) would look syntactically nicer, a new set of vendor options
would be likely easier to implement.

A dedicated visitor that takes zoom and turns it into equivalent scale denominator ranges, perhaps run right after
parsing, would simplify adoption, as there are many users of the scale denominators, streaming renderer is but one
of them, there’s also KML and vector tiles, feature info, scale dependent legends, just to mention the ones that came
to mind while writing this mail.

···

Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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Ian Turton

4

Andrea,

Please feel free to move them around as needed, your plan sounds great!

I have encountered one awkward difficult with the use of zoom levels as a very cheerful shorthand for scale denominator. I got a bit stuck on with mbox style where zoom level was defined with respect to web mercator.

At the time there were discussion of:

  1. Treat zoom-level as using referencing the grid set being drawn? I can see how this make sense (may have to pass in something from GWC)

  2. Treat zoom-level as always defined with respect to web mercator? This interacts well with normal SLD styles …

  3. Or have web mercator be the default, with an override (in the file or from the gridset being drawn)? Can lead to some confusion (it is hard to even describe).

I believe mbstyle uses option (2) which above.

···

Jody Garnett

Regards,

Andrea Aime

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Ing. Andrea Aime
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Technical Lead

GeoSolutions Group
phone: +39 0584 962313

fax: +39 0584 1660272

mob: +39 339 8844549

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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5

I have encountered one awkward difficult with the use of zoom levels as a very cheerful shorthand for scale denominator. I got a bit stuck on with mbox style where zoom level was defined with respect to web mercator.

At the time there were discussion of:

  1. Treat zoom-level as using referencing the grid set being drawn? I can see how this make sense (may have to pass in something from GWC)

  2. Treat zoom-level as always defined with respect to web mercator? This interacts well with normal SLD styles …

  3. Or have web mercator be the default, with an override (in the file or from the gridset being drawn)? Can lead to some confusion (it is hard to even describe).

Option 3 is what YSLD is using now. Default to web mercator unless specified otherwise (see “default value” for grid/name, along with name not being required).

I believe mbstyle uses option (2) which above.

The Mapbox Style spec nowadays supports a bunch of projections, but in a really odd way, they start with globally useful projections (e.g., equalEarth) and
then switch to web mercator as one zooms in.
The Maplibre Style spec instead allows to only use “globe” as an experimental feature.
If instead you’re referring to the gt-mbstyle module, I don’t see any attempt to support different gridsets or projections, the transaction from zoom to
scale denominator is delegated to a single function understanding only web mercator.

Cheers
Andrea

···

On Sun, Aug 11, 2024 at 1:24 AM Jody Garnett <jody.garnett@anonymised.com.> wrote:

6

Pull requests are available:

···

Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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Regards,

Andrea Aime

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phone: +39 0584 962313

fax: +39 0584 1660272

mob: +39 339 8844549

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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7

Thanks Andrea, the two PRs are now merged.

···

Jody Garnett

Regards,

Andrea Aime

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fax: +39 0584 1660272

mob: +39 339 8844549

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

This email is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. We remind that - as provided by European Regulation 2016/679 “GDPR” - copying, dissemination or use of this e-mail or the information herein by anyone other than the intended recipient is prohibited. If you have received this email by mistake, please notify us immediately by telephone or e-mail

Regards,

Andrea Aime

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Technical Lead

GeoSolutions Group
phone: +39 0584 962313

fax: +39 0584 1660272

mob: +39 339 8844549

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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8

Hi Jody,
I’ve noticed, thanks!

···

Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

This email is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. We remind that - as provided by European Regulation 2016/679 “GDPR” - copying, dissemination or use of this e-mail or the information herein by anyone other than the intended recipient is prohibited. If you have received this email by mistake, please notify us immediately by telephone or e-mail

Jody Garnett

Regards,

Andrea Aime

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fax: +39 0584 1660272

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

This email is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. We remind that - as provided by European Regulation 2016/679 “GDPR” - copying, dissemination or use of this e-mail or the information herein by anyone other than the intended recipient is prohibited. If you have received this email by mistake, please notify us immediately by telephone or e-mail

Regards,

Andrea Aime

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Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia.

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