How to identify which layer is on the top for a mosaic json tile?

[HangChenSatelytics]

Context:
Suppose I have a mosaic json file, inside which there are many "layers" that together they form the tile service. When those individual layers overlap, and I have a point on the overlapped location. How can I tell that beneath this point, which individual layer is on the top?

Investigation
Browsing through the repo, it looks like "assets_for_point()" function provide such utility, but it seems to give me a list of layers being identified. But which one is on the top?

Also, within MosaicTilerFactory, I found suspicious function "PixelSelectionParams" that seems to use the "first" strategy. Is this related to my question?

[vincentsarago]

How can I tell that beneath this point, which individual layer is on the top?

You can't tell this from each pixel, but if you want you can return the list of assets used (per tile) on the response header https://github.com/developmentseed/titiler/blob/main/src/titiler/mosaic/titiler/mosaic/factory.py#L348-L352

Browsing through the repo, it looks like "assets_for_point()" function provide such utility, but it seems to give me a list of layers being identified. But which one is on the top?

Well it will use the first of the list (if the pixel is not transparent)

To really know which asset is going to be use for a pixel you can use the /point endpoint and check which asset will return some values

I found suspicious function "PixelSelectionParams" that seems to use the "first" strategy.

it's not suspicious, it's the method used to select which pixel to choose from the stack of pixel https://cogeotiff.github.io/rio-tiler/mosaic/