Add elevation band

How to convert the ellipsoid elevation to sea level height after adding elevation band?

That’s not an easy task and if you need to do it you probably need to implement your own processor.

But maybe you explain your use case. Is the ellipsoid/geoid deformation of such importance for your use-case? Maybe there are other ways to workaround.

Thank you! I want to extract the coastal zone.
For example, extending 10 km from the shoreline to the land and extending to the -15 m isobath.