Add nodata flag to Class object?

[m-mohr]

To make it easier to detect (multiple) no-data values that are described using the Class Object, would you think that it makes sense to add a optional nodata boolean flag (default: false) to the class object? This could be a migration path for users that otherwise would be stuck with file extension v1.0.0.

cc @pjhartzell

[pjhartzell]

My experience with STAC thus far has been primarily on the creation side, not consumption. But I can see how this flag could be a useful way to unambiguously detect multiple no-data values, rather than having to parse the name or description fields.

That said, the examples where I've come across multiple no-data values are for "continuous" data, e.g., the VIIRS vegetation index products that have bands with a valid range of [-10000, 10000] and two no-data values of -13000 and -15000. If I were to add a classification extension to one of these bands, it would seem incomplete unless the valid data range was also described in a Class Object. I know this has come up before - thoughts?

[m-mohr]

That said, the examples where I've come across multiple no-data values are for "continuous" data, e.g., the VIIRS vegetation index products that have bands with a valid range of [-10000, 10000] and two no-data values of -13000 and -15000. If I were to add a classification extension to one of these bands, it would seem incomplete unless the valid data range was also described in a Class Object. I know this has come up before - thoughts?

Yes, as discussed yesterday this also applies for NOAA MRMS QPE. -1, -3 no-data, >= 0 valid values. It is incomplete, but that was what we agreed on, right? @pjhartzell At least, unless we add ranges.

[m-mohr]

Here's an example I created manually for QPE today:

{
  "type": "Feature",
  "stac_version": "1.0.0",
  "id": "CONUS_MRMS_MultiSensor_QPE_24H_Pass2_00.00_20220530-120000",
  "properties": {
    "noaa_mrms_qpe:pass": 2,
    "noaa_mrms_qpe:period": 24,
    "description": "Multi-sensor accumulation 24-hour (2-hour latency) [mm]",
    "datetime": "2022-05-30T12:00:00Z"
  },
  "geometry": {
    "type": "Polygon",
    "coordinates": [
      [
        [
          -130.0,
          55.0
        ],
        [
          -60.0,
          55.0
        ],
        [
          -60.0,
          20.0
        ],
        [
          -130.0,
          20.0
        ],
        [
          -130.0,
          55.0
        ]
      ]
    ]
  },
  "links": [
    {
      "rel": "collection",
      "href": "./collection.json",
      "type": "application/json",
      "title": "NOAA MRMS QPE 24-hour Pass 2"
    }
  ],
  "assets": {
    "cog": {
      "href": "MRMS_MultiSensor_QPE_24H_Pass2_00.00_20220530-120000.tif",
      "roles": [
        "data",
        "cloud-optimized"
      ],
      "type": "image/tiff; application=geotiff; profile=cloud-optimized",
      "raster:bands": [
        {
          "spatial_resolution": 1000,
          "unit": "mm",
          "nodata": -3,
          "data_type": "float64",
          "classification:classes": [
            {
              "value": -3,
              "name": "no-data",
              "description": "No coverage or missing value (no-data)",
              "nodata": true
            }
          ]
        }
      ],
      "proj:shape": [
        6553,
        4279
      ],
      "proj:transform": [
        1189.1837785492494,
        0.0,
        -14471533.80310966,
        0.0,
        -1189.1837785492494,
        7361866.113023454
      ],
      "proj:epsg": 3857,
    },
    "grib2": {
      "href": "MRMS_MultiSensor_QPE_24H_Pass2_00.00_20220530-120000.grib2",
      "roles": [
        "data",
        "source"
      ],
      "type": "application/wmo-GRIB2",
      "raster:bands": [
        {
          "spatial_resolution": 1000,
          "unit": "mm",
          "data_type": "float64",
          "classification:classes": [
            {
              "value": -1,
              "name": "missing-value",
              "description": "Missing value (no-data)",
              "nodata": true
            },
            {
              "value": -3,
              "name": "no-coverage",
              "description": "No coverage (no-data)",
              "nodata": true
            }
          ]
        }
      ],
      "proj:shape": [
        7000,
        3500
      ],
      "proj:transform": [
        0.009999999714244895,
        0.0,
        -129.99999999985712,
        0.0,
        -0.009999999714204058,
        54.9999999998571
      ],
      "proj:epsg": null,
      "proj:projjson": {
        "$schema": "https://proj.org/schemas/v0.4/projjson.schema.json",
        "type": "GeographicCRS",
        "name": "unknown",
        "datum": {
          "type": "GeodeticReferenceFrame",
          "name": "unknown",
          "ellipsoid": {
            "name": "unknown",
            "semi_major_axis": 6378160,
            "inverse_flattening": 298.253916296469
          }
        },
        "coordinate_system": {
          "subtype": "ellipsoidal",
          "axis": [
            {
              "name": "Longitude",
              "abbreviation": "lon",
              "direction": "east",
              "unit": "degree"
            },
            {
              "name": "Latitude",
              "abbreviation": "lat",
              "direction": "north",
              "unit": "degree"
            }
          ]
        }
      },
    }
  },
  "bbox": [
    -130.0,
    20.0,
    -60.0,
    55.0
  ],
  "stac_extensions": [
    "https://raw.githubusercontent.com/stactools-packages/noaa-mrms-qpe/main/extension/schema.json",
    "https://stac-extensions.github.io/raster/v1.1.0/schema.json",
    "https://stac-extensions.github.io/classification/v1.1.0/schema.json",
    "https://stac-extensions.github.io/projection/v1.0.0/schema.json"
  ],
  "collection": "noaa-mrms-qpe-24h-pass2"
}

[pjhartzell]

I'm a sucker for examples. 🙂

Yeah, I think this is fine. It's an optional field and it addresses a problem that we keep coming up against.

We can push off the use of a multiple values or a data range for value until later.

[drwelby]

Works for me too.

[m-mohr]

I opened an issue for the range issue... #33