Raster Palette

[kylebarron]

Was looking at this new public landcover dataset and pondering how to make a STAC that represents it. Seems like it could make sense to have palette/colormap values encoded in the raster extension?

[cholmes]

I think this is most in line with this 'values' mapping object that we had in file. It clearly doesn't belong in file, I recently realized it was still there and filed an issue - stac-extensions/file#6 I think we felt it was worth its own extension instead of putting it in raster, and @m-mohr started https://github.com/stac-extensions/classification I could also see it going directly in raster, but I'm forgetting why we didn't want it there. Though that's not quite all the way to the palette / color map. That could make sense in the 'rendering hints' extension, which I think I never quite got over the line, though most of the functionality desired ended up elsewhere.

Anyways, round about answer to say +1, would be great to have that somewhere. And I'd like to use it for Planet UDM data as well, to render our cloud / cloud shadow / clear / etc masks.

[m-mohr]

Yes, it would be great if someone could make a proposal based on file:values in the existing or a new repo. I won't have the time, unfortunately.

[kylebarron]

cc @lossyrob since he might be making a catalog on that dataset anyways, ref: https://twitter.com/lossyrob/status/1408450219793072130

[lossyrob]

The color maps are baked directly into the COG, in case that's useful info.

I'll take a look at this, not sure if I'll get time to fit in extension spec PR -> new version release -> PySTAC extensions changes before the API release...in case someone else wants to contribute that quickly (looking at you @kylebarron 😉 )

[emmanuelmathot]

A color palette metadata is totally inline with raster extension. It was initially proposed but postponed for a future version because it was not clear if color interpretation should be part of a kind of rendering hints extension.

Yes, it would be great if someone could make a proposal based on file:values in the existing or a new repo. I won't have the time, unfortunately.

Here, I am not sure we are all talking about the same thing. Values is more about data interpretation and would be larger than color definition only.

[kylebarron]

Here, I am not sure we are all talking about the same thing. Values is more about data interpretation and would be larger than color definition only.

Agreed there's a subtle difference here. Considering the original landcover dataset that made me start this issue, there's a colormap stored within the COGs that maps data values to colors, but that isn't really a sufficient interpretation. Ideally you'd want an association from data value to color and also title/description.

[lossyrob]

Would it make more sense to have this as part of the label extension? E.g. an optional property on the Class object for "color". @kbgg I think you or other RE folk had been looking at something related, cc'ing you in case there's thoughts here.

[m-mohr]

I think that it doesn't make much sense in my use case. The file:values right now is asset-based and as far as I understand the label extension is mostly item-based. Also, it requires numerous additional fields, which I don't need.

[m-mohr]

I'm finally going to need some kind of replacement for file:values, which allows me to express the interpretation (description) for values in each file and/or raster band. There are probably more use cases as indicated above so that's also why the idea was to make it a separate extension, but I won't have a lot of time to wait for this. So how can we proceed with this?

[m-mohr]

Would it make sense to make this a field that can be used in raster:bands and/or eo:bands and gives a mapping between values and corresponding metadata?

e.g. something like

...
"assets": {
  "data": {
    "href": "example.tif",
    "type": "image/tiff; profile=geotiff",
    "roles": ["data"],
    "raster:bands": [
      {
        "classification:values": [
          {
            "values": [0],
            "description": "Valid data",
            "color": "#000000"
          },
          {
            "values": [1],
            "description": "Clouds",
            "color": "#ffffff"
          },
          {
            "values": [2,3],
            "description": "Clouds Shadows",
            "color": "#cccccc"
          }
        ]
      }
    ]
  }
}
...

This is just a made-up example. Please change/expand/change with whatever your use-case requires.

If it keeps that simple, we may even add it to raster directly as values and remove it from file.

[emmanuelmathot]

For my understanding from your example: There would be a classification extension applicable at different level (asset or raster band), right?

[m-mohr]

Yes

[drwelby]

I have a couple days next week (Oct 4) I could devote to hashing out this topic and https://github.com/stac-extensions/classification.