The simSetSegmentationObjectID API as described here is somewhat limited, in particular:

• It is not possible to un-assign a segmentation ID so that it does not show up in the segmentation view (custom depth rendering disabled). In the neighbourhood environment, there are some leaves lying on the roads or the grass which I would like to just ignore for the segmentation so that they take on the segmentation ID of the underlying road or grass, respectively.

• There are objects that do not have a reasonable (or easily to look-up) object ID, such as spline mesh components or mesh components instantiated by a foliage actor. Especially spline mesh components have the same name as the landscape, so there is no way to distinguish them from the landscape. This applies to the road in the mountains landscape environment, or the power lines, fences or the path in the park in the neighbourhood environment.