Trouble setting assets with custom MultiBaseReader

[mccarthyryanc]

I have a custom MultiBaseReader that looks similar to this (much like STACReader), simplified a bit just to make this clear:

from typing import Type, Dict, Any

import attr
import rasterio
from rio_tiler.io.base import BaseReader, MultiBaseReader
from rio_tiler.io.rasterio import Reader
from rio_tiler.types import AssetInfo


@attr.s
class CustomReader(MultiBaseReader):

    def __attrs_post_init__(self):
        self.assets = ["/path/to/raster.tif"]
        self.bounds = [114.101509, 22.437414, 114.156379, 22.482232]
        self.crs = rasterio.crs.CRS.from_epsg(4326)
    
    def _get_asset_info(self, asset: str) -> AssetInfo:
        return AssetInfo(url=self.assets[0])

I am instantiating and calling tile (with x,y,z values that I know overlap the raster):

r = CustomReader(input="bogus")
r.tile_x=26772, tile_y=14282, tile_z=15)

But I get this error:

MissingAssets: assets must be passed either via `expression` or `assets` options.

Is there a way to pass assets via self.assets and have tile use them? Or do I need to update the tile method to assign from assets similar to info and statistics methods?:

assets = assets or self.assets

[vincentsarago]

@mccarthyryanc I'm not sure why you're using MultiBaseReader for this or maybe you're example is just too much reduced

a MultiBaseReader is designed to with an input dataset in format of {"asset1": "url1", "asset2": url2} and the assets list should be a list of asset keys ["asset1", "asset2"]

By default the tile() method will expect to have an assets option passed which will then be used to get the URL. So if I understand well, you want the tile() method to default to all assets? This could be quite dangerous for the majority of users (IMO). I will work well when you have a couple assets but if you have a STAC Item with 10 assets (with them having multiple bands) this could results in weird things.

Maybe we can introduce a default_assets attribute

[mccarthyryanc]

Yeah, sorry a little oversimplified 😅 I have an internal STAC-like API that I'm trying to work with, basically the same as the STACReader with a custom fetch function and a fixed asset list that I'd need to access at a time. That's why I was using MultiBaseReader.

A default_assets attribute would be helpful if it could read from self.assets. Where my CustomReader would define the default_assets and then tile (and the other similar methods part/point/etc.) would maybe do something like:

   def tile(
        self,
        tile_x: int,
        tile_y: int,
        tile_z: int,
        assets: Union[Sequence[str], str] = None,
        expression: Optional[str] = None,
        asset_indexes: Optional[Dict[str, Indexes]] = None,  # Indexes for each asset
        asset_as_band: bool = False,
        **kwargs: Any,
    ) -> ImageData:
...
        if expression:
            assets = self.parse_expression(expression, asset_as_band=asset_as_band)

        assets = assets or self.default_assets

        if not assets:
            raise MissingAssets(
                "assets must be passed via `expression`, `assets` options, or the class-level `default_assets`."
            )
...

If that sounds okay, I'd be happy putting together a PR.

[vincentsarago]

are you using titiler-pgstac?

[mccarthyryanc]

I'm not, just plain titiler. But I did look at that repo as an option. I'm not querying against postgres, so it seemed like that project did more than what I needed.

[mccarthyryanc]

I ended up creating a PR with a solution that is working really well for me. I added the attribute to STACReader so it was simpler to test and document. But, I totally understand if this isn't great to put in STACReader and happy to adapt.