Accessing and viewing imagery RGB bands data as separate COG files

[nicolasvila]

Hi,
I would like to serve RGB and display images from independent COG files stored on a S3 cloud storage.
Here are below some test COG files:

files = [
    "https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/36/Q/WD/2020/7/S2A_36QWD_20200701_0_L2A/B04.tif",
    "https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/36/Q/WD/2020/7/S2A_36QWD_20200701_0_L2A/B03.tif",
    "https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/36/Q/WD/2020/7/S2A_36QWD_20200701_0_L2A/B02.tif"
]

Is that possible using titiler to stream RGB image tiles generated from independent bands URLs?
That would also be great to pass a list of URL bands to the "map" viewer instead of a single COG URL.
Thanks.

[vincentsarago]

@nicolasvila this is absolutely possible but not with the default titiler application

you'll need to do something like https://github.com/developmentseed/rio-viz/blob/main/rio_viz/io/reader.py#L14-L54 and titiler MultiBandReader tiler factory

from typing import Any, Dict, List, Type

import attr
from braceexpand import braceexpand
from fastapi import FastAPI
from morecantile import TileMatrixSet
from rio_tiler.constants import WEB_MERCATOR_TMS
from rio_tiler.errors import InvalidBandName
from rio_tiler.io import BaseReader, MultiBandReader, Reader

from titiler.core.factory import MultiBandTilerFactory

@attr.s
class MultiFilesBandsReader(MultiBandReader):
    """Multiple Files as Bands."""

    input: Any = attr.ib()
    tms: TileMatrixSet = attr.ib(default=WEB_MERCATOR_TMS)

    reader_options: Dict = attr.ib(factory=dict)
    reader: Type[BaseReader] = attr.ib(default=Reader)

    files: List[str] = attr.ib(init=False)

    minzoom: int = attr.ib()
    maxzoom: int = attr.ib()

    @minzoom.default
    def _minzoom(self):
        return self.tms.minzoom

    @maxzoom.default
    def _maxzoom(self):
        return self.tms.maxzoom

    def __attrs_post_init__(self):
        """Fetch Reference band to get the bounds."""
        self.files = list(braceexpand(self.input))
        self.bands = [f"b{ix + 1}" for ix in range(len(self.files))]

        with self.reader(self.files[0], tms=self.tms, **self.reader_options) as cog:
            self.bounds = cog.bounds
            self.crs = cog.crs
            self.minzoom = cog.minzoom
            self.maxzoom = cog.maxzoom

    def _get_band_url(self, band: str) -> str:
        """Validate band's name and return band's url."""
        if band not in self.bands:
            raise InvalidBandName(f"{band} is not valid")

        index = self.bands.index(band)
        return self.files[index]


app = FastAPI()
endpoints = MultiBandTilerFactory(reader=MultiFilesBandsReader)
app.include_router(endpoints.router)

then you'll be able to pass url=https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/36/Q/WD/2020/7/S2A_36QWD_20200701_0_L2A/B{04,03,02}.tif

You'll also need to pass bands=b1&bands=b2&bands=b3 ("b" + index of the file in the list) for the tiler to select the correct files.

To be honest, for this it might just be easier to use STAC 😅

[nicolasvila]

Hi Vincent, and thanks for this quick answer !
Indeed STAC is the way to go and would be much better but in this particular case, it might not be available unfortunately.
This workaround could become an interesting feature, though :-)