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tilezen / joerd

Joerd can be used to download, merge and generate tiles from digital elevation data
MIT License
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What vertical reference is used in the tile data? #205

Closed jbroll closed 3 years ago

jbroll commented 3 years ago

It seems like the vertical reference system is not documented anywhere I've looked. It is EMG96?, WGS84 ellipsoid? Does the documentation clearly state this somewhere? Thanks!

nvkelso commented 3 years ago

Generally we assume WGS84 in data sources, or try to transform into WGS84 on ingest. But we haven't performed a full audit. Is there an geographic area or tile where you think there is a problem?

jbroll commented 3 years ago

I'm trying to understand how to convert the data to being ellipsoid referenced for a specific application. I understand how to do this but not what the height reference is for the tiles. Does WGS84 mean that it is referenced to EGM2008?

nvkelso commented 3 years ago

There is math documented on how to make the transformations, but that's out of scope for this project. WGS84 generally refers only to the XY coordinates, while EGM2008 also considers Z (height) and change over time because the planet is still shifting around.

jbroll commented 3 years ago

I'm not asking for help with the math. Do you know what the data in the tiles is referenced to?

pchilds commented 1 year ago

Why is this closed without an answer or update to the documentation? Is the final answer that they are all referenced to the spheroid then?