Request for sea level-terrain support

[mborjesson-bentley]

Feature

Hi!

We're in a situation where our customers need to use a sea level-terrain with CesiumJS. For now we have implemented this using our own TerrainProvider that fetches elevations from the Bing Elevation API. This works but the performance is not that great, so we would like to request an official implementation of a sea level-terrain. Preferably through Cesium ION, if possible.

Thanks!

[ggetz]

Hi @mborjesson-bentley, this may be a bit beyond the scope of just CesiumJS. 🙂 But I have a few questions to clarify that:

For my understanding, when you say sea level-terrain, is this the same as terrain with heights based on height above mean sea level (MSL)?

If so, do you plan on bringing your own terrain data, or to read out any height values in reference to MSL at runtime?

Thanks!

[ggetz]

CC #11786 (if this does relate to MSL values at runtime)

[mborjesson-bentley]

Hi @ggetz, thanks for your reply!

Yes, terrain using MSL. We've been using the Bing Maps Elevation API, we don't have any terrain data of our own. For now we're interested in visualizing the terrain and not reading any height values.

To clarify the problem, here's an example with a realitydata which is generated relative to sea level, which causes it to be placed below ground with the Cesium World Terrain:

Here's what it should look like with sea level-terrain:

[ggetz]

Got it, thanks for the explanation @mborjesson-bentley.

I'm curious about the reality data. I assume you are streaming it into CesiumJS using 3D Tiles.

Is there a specific reason why the 3D Tiles output is relative to MSL rather than the WGS84 ellipsoid? I ask because Cesium World Terrain is referenced against ellipsoid height, and I don't believe we're likely to build out a MSL version in the near future.

You can certainly adjust the height of the reality data 3D Tiles at runtime to compensate for the discrepancy. For instance, you could query a spatial service to determine the height discrepancy between MSL and WGS84 ellipsoid height at the location corresponding to center of the reality mesh. Then, use the modelMatrix property to offset the reality data 3D Tiles.

[ggetz]

I'm closing this issue due to inactivity. But if this does need more discussion, please feel free to re-open. Thanks!