How to get the min / max value to rescale using a mosaicJSON for dem COGs

[tdurand]

Hello,

I am trying to use titiler with the elevation dataset Copernicus DEM : https://registry.opendata.aws/copernicus-dem/

I have produced a Mosaic JSON using cogeo-mosaic for the entire COG dataset (16 MB) : https://filedn.com/lkrqWbAQYllSVUK4ip6g3m0/mosaic.json . (using the list of all the COGs here)

Then I use titiler to get tiles from it , for example: https://titiler.xyz/mosaicjson/tiles/12/1535/2322.png?url=https://filedn.com/lkrqWbAQYllSVUK4ip6g3m0/mosaic.json

But I get a grey tile

If I use some rescale rescale=0,2000 parameter to map the values to fit in the png format it works:

https://titiler.xyz/mosaicjson/tiles/12/1535/2322.png?url=https://filedn.com/lkrqWbAQYllSVUK4ip6g3m0/mosaic.json&rescale=0,2000

But my issue is that I do not know what is the min, max to specify , is it the min max of the whole dataset ? or the min max of the bunch of COG files used by the mosaic for this tile ?

For example for a single COG I can get the min/max info like this: https://titiler.xyz/cog/statistics?url=https://copernicus-dem-30m.s3.amazonaws.com/Copernicus_DSM_COG_10_N08_00_W068_00_DEM/Copernicus_DSM_COG_10_N08_00_W068_00_DEM.tif

My question would be, what is the best way to set the rescale= parameter in case of a mosaic ?

Thanks a lot

Thibault

[vincentsarago]

When using the rescaling parameter, this should be the min/max values for the whole dataset.

https://titiler.xyz/mosaicjson/map?url=https://filedn.com/lkrqWbAQYllSVUK4ip6g3m0/mosaic.json&rescale=0,6000&colormap_name=terrain

☝️ tiles will start loading at zoom 8

Note: we've added Copernicus DEM to rio-tiler-pds which in theory remove the need of creating MosaicJSON for this dataset.

from rio_tiler_pds.copernicus.aws.dem import Dem30Reader 
from titiler.core.factory import TilerFactory

# We need to overwrite the default `url` path parameter
def path_dep() -> str:
    return "copernicus_dem"


from fastapi import FastAPI

app = FastAPI()

endpoints = TileFactory(
    reader=Dem30Reader,
    path_dependency=path_dep
)
app.include_router(endpoints.router)

[tdurand]

When using the rescaling parameter, this should be the min/max values for the whole dataset.

Thanks ! Yes in the meantime I figured out that, I have set to 0,8900 I should be fine 😅

Note: we've added Copernicus DEM to rio-tiler-pds which in theory remove the need of creating MosaicJSON for this dataset.

Ahh good to know, I will have a look. anyways it was a good exercise to generate a mosaic json myself, will be useful for future needs.

Thanks a lot !