Rendering networks on terrain surface & controlling point geometry symbology in iTwin.js

[GediminasSeib]

I’ve been working with network geometry that spans around 1000s of km2, represented in the iModel using GeometricElement3d. I have two questions regarding how iTwin.js handles geometry rendering and symbology:

1. Rendering Networks on Terrain Surface

   Our network nodes and links currently don’t have Z values. And in the iTwin viewer (even with the terrain off) the geometry appears below the map. The vertical offset is small at the center of the model but increases toward the edges.

• Is there a way to configure the iModel so that these geometries are automatically draped or rendered on the terrain surface?

2. Controlling Symbology for Point Geometries

   For nodes with point geometry, I’ve found that it’s possible to change their weight. However, setting a fixed size doesn’t scale well when zooming in and out.

• Is there a way to further control their symbology in the viewer?
• For example can we define custom marker symbols?
• Is it possible to adjust size properties dynamically?

Any guidance, examples, or references to relevant APIs would be greatly appreciated!

[pmconne]

Hi @GediminasSeib,

In what coordinate system is your geometry defined? Is it in ECEF, accounting for the curvature of the Earth? Or, is it in some arbitrary cartesian coordinate system where Z is assumed to correspond to ground level everywhere? If the latter, does your iModel define a geographic coordinate system to allow us to project your geometry onto the globe? If you disable terrain and the globe by setting GlobeMode.Plane to make the background map flat, does the geometry align better?

We don't currently support custom marker symbols for point geometry. You could write a FeatureOverrideProvider that dynamically adjusts the point size override based on the current zoom level.

[GediminasSeib]

Thanks for the answer regarding symbology. Regarding ECEF: the geometry itself is not defined in ECEF coordinates, we're assuming that Z corresponds to ground level throughout the model. For context, I'm using the following setup:

this.iModelDb.setEcefLocation(EcefLocation.createFromCartographicOrigin(featureCenter));
this.iModelDb.setGeographicCoordinateSystem({
   horizontalCRS: { id: 'EPSG:4979' },
   verticalCRS: { id: 'ELLIPSOID' },
 });

Disabling both terrain and the globe using GlobeMode.Plane doesn't seem to improve alignment the vertical offset still increases toward the edges.
Additionally, I'm currently viewing the iModel through iTwin Experience, where the Cesium viewer introduces a small Z offset due to terrain, but it's consistent across the model. However, in the iTwin Viewer, as mentioned earlier, the vertical offset is minimal at the center but grows toward the edges.