Spatial Reference

[Wade]

If there is a scene coordinate system of 3826, There is also a layer of 4326. Can it be directly converted to 3826 and put in the scene?

[ArnoFiva]

This really depends on the layer type, can provide more information? For example, noncached layers such as feature layers are automatically reprojected for you by the ArcGIS API for JavaScript. Other layer types such as raster or scene layers need to be reprojected and republished first using for example ArcGIS Pro.

For more information what coordinate systems are supported in 3D (SceneView) and how they apply to global and local scenes, see the following section: 
https://developers.arcgis.com/javascript/latest/api-reference/esri-views-SceneView.html#supported-co...