Issue rendering singleband image with colormap via stac endpoint

[aliasmrchips]

In particular, if I follow the rasterio example and create a "colormap.tif". Loading the image directly using the cog endpoint works just fine.

However, if I create a STAC item and use the stac endpoints, it appears to ignore the internal colormap.

I can't figure out what the difference is. Please help!

[vincentsarago]

Thanks @aliasmrchips for the question.
You are right, the STACReader (used in the /stac) endpoint is loosing the information about the internal colormap of the item. This is by design and sadly there isn't an easy way of fixing this.

when you are using the /cog endpoint, you are using https://github.com/cogeotiff/rio-tiler/blob/master/rio_tiler/io/cogeo.py#L28 and

titiler/titiler/endpoints/factory.py

Lines 320 to 322 in a95073d

	colormap = render_params.colormap or getattr(
	src_dst, "colormap", None
	)

☝️ in this, if the COGReader instance has a colormap variable, it will be used by default, and that's what you are getting.

For /stac, we are using a specific reader based on https://github.com/cogeotiff/rio-tiler/blob/master/rio_tiler/io/base.py#L334 which enable reading multiple assets in parallel (and merging the results), sadly with the STACReader we CANNOT keep the colormap for each asset 🙁.

If the assets in your items do not need to be merged (which is what we do when multiple bands are stored as multiple assets), I would advise to switch to the /cog/ endpoints.

Another solution would be to register a custom colormap (if the colormap in your data never change) and to use it to colorize your result

1. custom cmap: https://github.com/developmentseed/titiler/blob/master/titiler/custom/cmap.py#L10-L21
2. register a cmap to rio-tiler colormap https://github.com/developmentseed/titiler/blob/master/titiler/dependencies.py#L27
3. create a enum : https://github.com/developmentseed/titiler/blob/master/titiler/dependencies.py#L32-L34
4. create a dependency using your cmap https://github.com/developmentseed/titiler/blob/master/titiler/dependencies.py#L316-L343

Note: I'll update the docs to clearly explain how to create/register a custom colormap

[aliasmrchips]

Maybe you can clarify something for me... if I have checked out the repo (and deployed following the aws lambda directions) I won't actually see any changes if I redeploy because the lambda Dockerfile is actually installing titiler from pypi?

[vincentsarago]

absolutely, the AWS cdk code is an example, to deploy your own custom code using TiTiler you'll have to create some custom CDK code

• https://github.com/developmentseed/titiler-pds
• https://github.com/developmentseed/titiler-mvt
• https://github.com/developmentseed/titiler-digitaltwin

[vincentsarago]

OR you could create your own cog/stac endpoint using a custom COG/STAC reader like 👇

import attr
from rasterio.io import DatasetReader
from rio_tiler.io.stac import fetch, _to_pystac_item
from rio_tiler.io import COGReader

import pystac

@attr.s
class CustomSTACReader(COGReader):
    """Custom COG Reader with GCPS support."""

    # This will keep the STAC item info within the instance
    item: pystac.Item = attr.ib(default=None, init=False)

    def __attrs_post_init__(self):
        """Define _kwargs, open dataset and get info."""
        # get STAC item URL and asset name
        asset = self.filepath.split(":")[-1]
        stac_url = self.filepath.replace(f":{asset}", "")

        # Fetch the STAC item
        self.item = pystac.Item.from_dict(fetch(stac_url), stac_url)

        # Get asset url from the STAC Item
        self.filepath = self.item.assets[asset].get_absolute_href()
        super().__attrs_post_init__()

with CustomSTACReader("https://canada-spot-ortho.s3.amazonaws.com/canada_spot_orthoimages/canada_spot5_orthoimages/S5_2007/S5_11055_6057_20070622/S5_11055_6057_20070622.json:pan") as cog:
    print(cog.bounds)

>>> (-111.87793996076493, 60.48627186654449, -109.94924666908423, 61.42036313093244)

then just create a custom tiler using the tiler factory

from titiler.endpoints.factory import TilerFactory

stac = TileFactory(reader=CustomSTACReader)

[aliasmrchips]

Thanks for the quick response and detailed explanation!

[vincentsarago]

FYI, in 0.2.0 we added custom colormap in the query parameter

/stac/preview?assets=B1&colormap='{"0": "#000"....}'

[aliasmrchips]

Awesome! However, I can't seem to get it to work... do you have an exact example? I assume I am doing something wrong encoding the dictionary in the url.

[vincentsarago]

do you have an error message to share?

you can also have a look at

titiler/tests/routes/test_cog.py

Lines 225 to 241 in 287201a

	cmap = urlencode(
	{
	"colormap": json.dumps(
	{
	"1": [58, 102, 24, 255],
	"2": [100, 177, 41],
	"3": "#b1b129",
	"4": "#ddcb9aFF",
	}
	)
	}
	)
	response = app.get(
	f"/cog/tiles/8/53/50.png?url=https://myurl.com/above_cog.tif&bidx=1&{cmap}"
	)
	assert response.status_code == 200
	assert response.headers["content-type"] == "image/png"

[aliasmrchips]

The error message is

{
detail: "Expecting value: line 1 column 1 (char 0)"
}

or some variation.

Adapting the example above does work.

Thanks again!

[vincentsarago]

yeah, make sure the colormap is a json string and urlencoded

[aliasmrchips]

How would you pass in a gradient colormap, like "viridis" (if it was not a named colormap), for example?