Support for vector virtual variables and tile generation

[srstsavage]

It would be great if xreds could create virtual variables from scalar component variables based on standard names (e.g. eastward_sea_water_velocity and northward_sea_water_velocity are detected and a virtual vector variable sea_water_velocity with magnitude and direction is created, and rendered tiles represent magnitude as grid color and direction as an arrow or barb, etc).

Some ncWMS code detecting vectors:

https://github.com/Reading-eScience-Centre/edal-java/blob/6cf2e669fffe0f4701297ac385c1ecd1c6047627/cdm/src/main/java/uk/ac/rdg/resc/edal/dataset/cdm/CdmDatasetFactory.java#L241

Any thoughts on the desirability of this behavior, or how it should be implemented? Core behavior, or in a plugin or extension?

[abkfenris]

Matt and I were recently chatting about this (I was thinking winds), and I'd love to see this as more generalized Xpublish plugin.

Maybe we hack something up during the code sprint?

[srstsavage]

Ah, yes! Would totally make sense as a general xpublish plugin so it can be used elsewhere.

Would it make more sense to move this discussion to https://github.com/orgs/xpublish-community/discussions?

[abkfenris]

Ya, I think it's probably worth considering them as a whole new type of plugins.

While there is a way to make them with the existing dataset providers, that may not work as soon as folks get creative and replace them (like Matt's subsetting plugin), so we probably want to make them explicit so they can be reused.

[mpiannucci]

@srstsavage So we have to support virtual variables in a few different ways already and its not fully fleshed out, but here is a quick overview:

• Extension API in XREDS (for now) that allows for transofrmations on a dataset at load time. This example adds a virtual MLLW or IGLD85 water level variable to provided datsets https://github.com/asascience-open/xreds/blob/main/xreds/extensions/vdatum.py
• xpublish-wms originalyl supported grouping originally like ncwms but we mvoed away from it towards our internal proxy service doing the grouping (example: https://oceansmap.com/link/ZjzMiZNPTw6YMjBgbLhAMw) But i would love to revisit this

I would like to see the extension behavior be xpublish native as well so i agree with alex

[abkfenris]

General discussion over https://github.com/orgs/xpublish-community/discussions/25