Validate accuracy of Sun and Shadows in Omniverse Create

[r-veenstra]

Omniverse Create has built in sun/shadow geo-location tools. Validate the default lighting setup works well with the positions of our tilesets

[r-veenstra]

I have reviewed the lighting setup in Omniverse, and compared to the current Cesium lighting setup in Unreal

I've gone through the following process to test and validate results:

• Setup a UE5 project using the San Francisco photogrammetry dataset.
• Configure lighting to an early morning time to create long shadows, in summer to ensure minimal north/south distortion
• Export this photogrammetry data, a camera, and the directional light from the UE5 sun study to USD - use Y-up to ensure alignment with the same photogrammetry in Omniverse (Note: UE5 USD exporter will export any loaded photogrammetry in UE5 to USD Prims which is useful for confirming alignment of data)
• Setup an Omniverse project using the same San Francisco photogrammetry dataset, along with the same geo-referencing details
• Import the UE5 USD into Omniverse and confirm it aligns perfectly with the Cesium for Omniverse data (it does!)
• Configure the Omniverse Sun Study tool with the same geo-location, time and date values as UE5 in the hope both tools will calculate the same sun position
• Compare results of the imported light from UE5, with the Omniverse Sun Study light

Note: After ensuring the UE5 USD aligned with the photogrammetry, tests needed to be conducted with Fabric turned off, as the dynamic Sun Study tool is not yet compatible with Fabric. Shadows were cast onto the USD Photogrammetry prims imported from UE5, which were confirmed to align perfectly with Cesium for Omniverse prims.

UE5 scene details:

Findings:

1) North direction for our datasets in Omniverse aligns to -Z in world space

2) When using the Omniverse Top orthographic viewport, south (+Z world space) is pointing to the top of the viewport, or what users might typically assume to be "North". This will be misleading for users as it will appear the world is "upside down", however see point 3...

3) We probably cannot rotate the data imported into Omniverse to resolve this, as it would cause imports from other packages (eg. data imported from Unreal Engine using Cesium for Unreal) to not align correctly. (Currently a Y-up export from the same dataset in UE5 will line up with Omniverse perfectly) @lilleyse @weegeekps we may want to discuss

4) So the user needs to be aware that the Top viewport is facing south. This should be added to tutorial documentation

5) The default geo-referenced light position in Omniverse appears to use positive +X in world space for North.

6) Here are both light sources turned on - green light is from UE5 and is the expected lighting direction based on the CesiumSunSky actor in UE5. Note it is different to the Omniverse light direction.

7) To obtain somewhat accurate shadows, the North Orientation value in the Sun Study location needs to be set to 90. Note, when comparing to the lighting exported from UE5 using the same time and location values, there is still a small discrepancy. It is currently unclear what this is caused by.

Key takeaways:

• Be careful about relying on the orientation of the top viewport or Z direction in world space
• Sun Study location needs to be set to 90 degrees to ensure somewhat accurate shadows