Cesium for Revit

Cesium ion
1

Hello, I used the Cesium plug-in to export some models to Cesium Ion but came across some issues with the results.

One of the exports came in too low with the objects being buried in the ground.

image
image1920×989 198 KB

The second export has model elements scattered around and detached from each other.

2025-01-21_16-49-17
2025-01-21_16-49-171920×989 106 KB

Any advice how to avoid this?

Thanks

1 Like
2

Welcome to the Cesium community.

Sorry to hear that you are having trouble getting your data correctly positioned. If you are just looking for a good visual fit you can adjust the height in the tileset position editor to place the asset at the right location.

I have reached out to our Revit Plugin team to provide some additional assistance about getting the data exported from Revit. In the mean time can you provide us with some additional information to help give you a better answer?

  • Are you able to share the asset id that you are having problems with?
  • Do you know what coordinate system you were using for your Revit data?
  • Was the Revit data based on the WGS84 ellipsoid heights or the local terrian height?
3

Thanks for getting back so quickly.

Asset Id for the model which is positioned too low is 2992550.
2992625 is for the model which has been pulled apart.

Coordinate system is UTM84-30N. The base data actually comes from Forma and the site information has been imported automatically but I am seeing the same result when setting the coordinates manually with latitude, longitude and local X and Y coordinates.

Height is based on local terrain elevation. Google Earth does provide a similar read-out.

I am thinking the earth geoid is not taken into account.

Sample Revit file attached. It contains no confidential information.

CoalRoad.zip (15.2 MB)

4

Hi @Johannes-lab,

When the data is transformed into geographic coordinates, Cesium ion assumes height is relative to the ellipsoid. This is why the turbines are appearing underground.

What you can do is tell Cesium ion that the provided data height is relative to a geoid instead. You can do this by adding +3855 to your EPSG code, like below. This tells ion your data height is relative to EGM2008. You can also substitute this for other geoids if needed, provided they have a valid EPSG code.

image
image396×398 10.3 KB

This is the data relative to Cesium World Terrain when exported using 32630+3855

image
image1270×582 67.9 KB

Can you provide the second export model? This looks like a potentially different issue.

5

Hi Ryan,

This is great! I didn’t know about this before. Thanks.

I attached the 2nd model.
ScoutMoorTopo.zip (23.3 MB)

6

@Johannes-lab I have tested with our latest development add-in, which has a number of changes to the way we calculate transforms for exported geometry, including instances.

With this export, it looks like the transform issues are resolved as you can see in the image below.

image
image1382×717 86.3 KB

We’re aiming to have these updates out with our February releases.

1 Like
7

Thanks Ryan,

I will keep an eye out for the updated version.