About elevation reference for cesium

CesiumJS
1

What is the elevation reference for the terrain data loaded by Cesium? Is it Egm96?

2

Hi there, it’s referenced against WGS84.

4

Which means the elevation of the terrain service (. terrain) is the reference ellipsoid height of wgs84?

5

@newpeople123

Thanks for your follow up.

I think you are asking about external services used to create DEM files in the .terrain format, and whether they output data in reference to the WGS84 ellipsoid or an orthometric height (like EGM96), right?

I am not sure which tool you are using. If it is Cesium Terrain Builder (CTB) GitHub - geo-data/cesium-terrain-builder: A C++ library and associated command line tools designed to create terrain tiles for use in the Cesium JavaScript library - which I should mention is not our tool and we do not maintain it - then a quick glance at the “recommendations” section of the docs tells be yes they do output terrain in reference to WGS84.

  • For performance reasons it is recommended that the input raster be in the same spatial reference system as the output tile grid in order to bypass the need to reproject the data. For terrain data this is World Geodetic System (WGS 84). If the source data is in another spatial reference system, however, the tool will attempt to reproject the data but with an associated performance penalty.

If you are using a different tool, you should check the docs for that tool.

Hope that answers your question and if not please follow up and we would be happy to try to help more.

Best,
Luke

7

Thank you for your reply.
As you mentioned, the CTB tool requires the input terrain coordinate system to be WGS84. But my question has nothing to do with external tools. What is the elevation reference of .terrain ormat itself? Is it the ellipsoid height of WGS84? Or is it orthometric height (such as EGM96)?

8

Hi @newpeople123.

Thanks for your follow up.

Cesium expects .terrain files to be referenced against WGS84 as mentioned above in the thread About elevation reference for cesium - #2 by Gabby_Getz

If that does not answer your question, do you mind explaining your use case more thoroughly so I can understand what you are asking?

Thank you!
Luke