STAC: Combine asset + GCPS + cutline

[vincentsarago]

Let's say that you have a non-geo asset (old map image) and a set of GCPS points and a cutline (WKT), I think it could be nice to embed everything in a STAC Item and then use a custom STACReader (built on top GCPSReader) to automagically mask/reproject your asset 🤷

{
    "type": "Feature",
    "stac_version": "1.0.0",
    "id": "boston",
    "properties": {
        "datetime": "2023-03-02T21:12:38.390386Z"
    },
    "geometry": {
        "type": "Polygon",
        "coordinates": [
            [
                [
                    -71.12109003469376,
                    42.31024457895685
                ],
                [
                    -71.10602473306288,
                    42.31024457895685
                ],
                [
                    -71.10602473306288,
                    42.32079384410276
                ],
                [
                    -71.12109003469376,
                    42.32079384410276
                ],
                [
                    -71.12109003469376,
                    42.31024457895685
                ]
            ]
        ]
    },
    "links": [],
    "assets": {
        "asset": {
            "href": "https://raw.githubusercontent.com/developmentseed/titiler-image/main/tests/fixtures/boston.tif",
            "titiler:cutline": "POLYGON ((100 100, 7596 100, 7596 5252, 100 5252, 100 100))",
            "titiler:gcps": [
                {
                    "resourceCoords": [
                        3011,
                        1187
                    ],
                    "coordinates": [
                        -71.11313846819577,
                        42.31750853403672
                    ]
                },
                {
                    "resourceCoords": [
                        5241,
                        5053
                    ],
                    "coordinates": [
                        -71.11414794574848,
                        42.31229871703916
                    ]
                },
                {
                    "resourceCoords": [
                        5615,
                        351
                    ],
                    "coordinates": [
                        -71.10904954715107,
                        42.31648965975142
                    ]
                },
                {
                    "resourceCoords": [
                        7012,
                        3894
                    ],
                    "coordinates": [
                        -71.11068726339353,
                        42.312086619361835
                    ]
                }
            ],
            "roles": []
        }
    },
    "bbox": [
        -71.12109003469376,
        42.31024457895685,
        -71.10602473306288,
        42.32079384410276
    ],
    "stac_extensions": [
        "https://developmentseed.org/stac-extensions/titiler/v1.1.0/schema.json"
    ]
}

Note:
there is a PR over the raster extension to add gcps as a external link: stac-extensions/raster#38 (I want them directly in the stac items)

Then imagine having all items in a pgstac database and be able to mosaic them with titiler-pgstac ;-)